There are few continuous palaeoenvironmental records spanning the Holocene in Andean Southern Patagonia near the Northern Patagonian Ice Field (~47°S). Insights into the environmental context for human–landscape interactions have relied mostly on data extrapolated from distant extra-Andean locations that suggest limited environmental change during the Holocene. La Frontera (46°52'S), a high altitude site on the southern beech forest–steppe ecotone boundary in the Río Zeballos valley, provides lithostratigraphical and palaeoecological evidence, constrained by 14C dating and tephrochronology, for dynamic environmental change during the last ~8000 years. An initial amelioration in environmental conditions after c. 8210 cal. BP was followed by a reversal to colder conditions between c. 7420 and 6480 cal. BP, coincident with initial human occupation within the Paso Roballos and Lago Pueyrredón basin. Between c. 6480 and 3700 cal. BP, the woodland/steppe composition continued to fluctuate in response to climatic change. After c. 3700 cal. BP, a gradual shift to more stable and temperate conditions, punctuated by increased fire activity, is contemporary with the later phases of human occupation extending up into the Paso Roballos–Río Zeballos corridor.
Organic molecular markers determined in a sediment core (V95-1A-1P) from Lake Victoria (East Africa) were used to reconstruct the history of human impact and regional fire activity during the Early Iron Age (~2400 to ~1100 yr BP). Fire history was reconstructed using levoglucosan and polycyclic aromatic hydrocarbons (PAHs) as markers for biomass burning that demonstrate two distinct fire periods peaking at 1450–1700 and 1850–2050 cal. yr BP. A partial correlation between levoglucosan and PAHs is interpreted as different transport behaviors and burn temperatures affecting the proxies. A fecal sterol index (CoP-Index) indicates the presence of humans near the lakeshore, where the CoP-Index lags a few centuries behind the fire peaks. The CoP-Index peaks between 1850 and1950 cal. yr BP and between 1400 and 1500 cal. yr BP. Retene, a PAH that indicates softwood combustion, differs from other PAHs and levoglucosan by abruptly increasing at ~1650 cal. yr BP and remaining high until 1200 cal. yr BP. This increase may potentially signal human activity in that the development of metallurgy and/or ceramic production requires highly efficient fuels. However, this increase in retene occurs at the same time as severe drought events centered at ~1500 and ~2000 yr BP where the droughts and associated woodland to grassland transition may have resulted in more intense fires. The grassland expansion could have created favorable conditions for human activities and triggered settlement growth that in turn may have created a positive feedback for further landscape opening.
Relative sea level (RSL) changes and the palaeogeography of a Neolithic hunter-fisher-gatherer settlement site on the former shore of the Gulf of Finland in the city centre of Tallinn were reconstructed by implementing GIS in landscape modelling based on archaeological, sedimentary and shore displacement data. AMS radiocarbon dating of mammal bones from the cultural layer suggests the existence of the hunter-fisher-gatherer settlement around 5.1–4.8 cal. ka BP on a seaward inclining sandy beach of Tallinn palaeo-bay c. 100 m from the Litorina Sea shoreline and at about 2.4 m above the coeval sea level. The shoreline passed the study site at about 5.8 cal. ka BP and retreated towards northeast with an average speed of 13 m per century, while the RSL lowered by c. 2.5 mm annually. Combining radiocarbon dates of terrestrial and marine mammal bones from the Neolithic cultural layer, a marine reservoir effect of 350 14C years for the brackish-water Baltic Sea was calculated. By using high-resolution archaeological data in combination with RSL and other geological proxies, we demonstrate new possibilities to reconstruct the palaeoenvironment of deeply buried coastal settlement sites and to predict a possible continuation of the cultural layer in heavily built-up areas.
The mid-Holocene was the warmest segment of the current interglacial and possessed a weak latitudinal temperature gradient, which impacted climate teleconnections and thus precipitation variability. Our window into the mid-Holocene climate is a high-resolution (near annual) stalagmite stable isotope-based paleoprecipitation record from Brown’s Cave in West-Central Florida. The oxygen isotopic (18O) time series is tied to a uranium-series (U-series) chronology that covers a 2000-year period from 6.6 to 4.6 ka. We compared our reconstruction with another speleothem 18O-derived precipitation record near our study area that spans the last 1600 years. That comparison shows that the mid-Holocene was drier than the last 1.6 millennia. We posit the cause of this aridity was a westward expansion of the North Atlantic Subtropical High (NASH) coupled with changes in the planetary boundary layer in the Gulf of Mexico. Time-series analysis of our oxygen isotopic record found little evidence of any teleconnections originating from the North Atlantic including the North Atlantic Oscillation during the mid-Holocene. However, there is some indication of a weak, quasi-persistent oscillation within the temporal periodicity of the Atlantic Multidecadal Variability.
Two sediment cores from the Chukchi Sea margin north of Alaska were analyzed for palynological composition including terrestrial and aquatic palynomorphs. Based on 13 radiocarbon ages, the investigated sedimentary record represents most of the Holocene with a century to multidecadal age resolution. Three palynological zones were discriminated based on the abundance of major palynomorph groups (terrestrial and freshwater palynomorphs and dinoflagellate cysts) and composition of spore and pollen assemblages. They are interpreted in terms of depositional and paleoclimatic changes including predominance of redeposition by meltwater or sea ice in the early-Holocene, a strong input of contemporaneous material related to Pacific water advection culminating after ca. 6000 yr BP, and more subtle changes in the late-Holocene. It is concluded that depositional environments, such as current transportation and mixing, have an overall major control on palynomorph distribution. The climatic factors may have also played an important role in palynomorph abundance and composition, especially in the middle- to late-Holocene, when circulation changes were less dramatic than during the flooding of the Bering Strait and the shallow Chukchi Sea shelf. Comprehending these linkages requires a better knowledge of the Holocene vegetation history in the coastal areas of Alaska and Chukchi Peninsula.
We test several methods of ostracod-based palaeoenvironmental reconstruction using indicator species approach, mutual ecological/climatic range methods, transfer functions, modern analogue technique and morphological variation within Cyprideis torosa in reconstructing the site evolution of a late Quaternary small lake basin in Thuringia, Central Germany. Sediment sections containing a diverse ostracod fauna were studied and compared with those from modern water bodies of Thuringia. Palynological investigations were executed to reconstruct the environmental conditions in the catchment area and for a obtaining a biostratigraphical framework. The brackish water ostracod Cyprideis torosa as well as the foraminifer Haplophragmoides indicate phases of saline groundwater influence, fed by salt bearing sediments of the Triassic basement. The accompanying freshwater ostracod fauna, however, reflects only low variations of salinity and temperature. Environmental changes in salinity, temperature and ecological stability indicated by microfossils and pollen are caused by an interplay of climatic shifts and the local geological and hydrological setting.
While the possibility of indigenous rice cultivation cannot be entirely ruled out, there is increasing evidence suggesting that rice farming was introduced to South China during the late-Holocene. However, determination of the exact timing of the spread of rice farming to South China is fraught with the lack of reliable radiocarbon dates. In this article, we present 15 new AMS 14C dates of charred plant remains recovered from late-Holocene sites of Shixia and Guye in Guangdong Province of South China. Our new AMS 14C dates suggest a later arrival of rice farming in the Pearl River Delta than previously thought. These new AMS 14C dates will shed new lights to an improved understanding of the environmental background and ecology of the southward spread of rice farming.
Boxcore 99LSSL-001 from the southwest Canadian Arctic Archipelago (68.095°N, 114.186°W), studied by multiproxy approaches (sea-ice diatom biomarker IP25, phytoplankton-based biomarker brassicasterol, biogenic silica, total organic carbon, dinoflagellate cysts = dinocysts, diatoms) and their applications (sea-ice index PBIP25, modern analogue technique (MAT) transfer functions), provides a chronologically constrained (210Pb, 137Cs, two 14C dates) palaeoenvironmental archive spanning AD 1625–1999 with which to compare and evaluate proxies frequently used in sea-ice reconstructions. Whereas diatoms are rare, PBIP25, biogenic silica and qualitative dinocyst approaches show good agreement, suggesting that palaeo sea-ice histories based on biomarker and microfossil techniques are robust in this region. These combined approaches show fluctuating long open water to marginal ice zone conditions (AD 1625–1740), followed by high-amplitude oscillations between long open water and extended spring/summer sea ice (AD 1740–1870). Greater ice cover (AD 1870–1970) precedes recent reductions in seasonal sea ice (AD 1970–1999). Dinocyst-based MAT, however, produces a low-amplitude signal lacking the nuances of other proxies, with most probable sea-ice reconstructions poorly correlating with biomarker-based histories. Explanations for this disagreement may include limited spatial coverage in the modern dinocyst distribution database for MAT and the broad environmental tolerances of polar dinocysts. Overall, PBIP25 provides the most detailed palaeo sea-ice signal, although its use in a shallow polar archipelago downcore setting poses methodological challenges. This proxy comparison demonstrates the limitations of palaeo sea-ice reconstructions and emphasizes the need for calibration studies tying modern microfossil and biogeochemical proxies to directly measured oceanographic parameters, as a springboard for robust quantitative palaeo studies.
The late-Holocene expansion of the Tupi–Guarani languages from southern Amazonia to SE South America constitutes one of the largest expansions of any linguistic family in the world, spanning ~4000 km between latitudes 0°S and 35°S at about 2.5k cal. yr BP. However, the underlying reasons for this expansion are a matter of debate. Here, we compare continental-scale palaeoecological, palaeoclimate and archaeological datasets, to examine the role of climate change in facilitating the expansion of this forest-farming culture. Because this expansion lies within the path of the South American Low-Level Jet, the key mechanism for moisture transport across lowland South America, we were able to explore the relationship between climate change, forest expansion and the Tupi–Guarani. Our data synthesis shows broad synchrony between late-Holocene increasing precipitation and southerly expansion of both tropical forest and Guarani archaeological sites – the southernmost branch of the Tupi–Guarani. We conclude that climate change likely facilitated the agricultural expansion of the Guarani forest-farming culture by increasing the area of forested landscape that they could exploit, showing a prime example of ecological opportunism.
Vegetation reconstructions rest on modern vegetation–pollen rain relationships and deductive reasoning. Establishing this relationship is a nontrivial task because differences among pollen assemblages are not necessarily proportional to differences in vegetation. This task is particularly challenging in Patagonia, where some tree taxa have indistinguishable pollen, and pollen grains can be transported long distances. In this study, we describe the modern pollen of 48 lake and wetland samples from northern Patagonia (40.5–44°S) to better discriminate the major vegetation zones of the region through pollen analysis. Specifically, we focus on the performance of three methodological approaches, namely, pollen indicators, classification trees, and optimal thresholds of dissimilarity. As a proof of concept, we use the modern pollen–vegetation relationships to reconstruct the vegetation history at Laguna el Trébol (41.07°S; 71.5°W). Our results revealed that (1) pollen sums exceeding 260 grains ensured replicable vegetation reconstructions, (2) modern vegetation zones could not be separated solely by visual inspection of their pollen spectra, (3) the classification tree and optimal thresholds of dissimilarity permitted discrimination of most vegetation zones, (4) detection of nonanalog communities required use of pollen indicators or optimal thresholds of dissimilarity, and (5) vegetation at L. el Trébol was likely dominated by late glacial shrubland with no modern analogs in the study area (15,000–12,180 cal. yr BP), modern shrubland (12,180–6500 cal. yr BP) and mixed forest (6500 cal. yr BP–present). This study allows a more realistic understanding of the pollen–vegetation relationship and provides new tools for interpreting past vegetation in northern Patagonia.
Deciphering the climate changes that influenced the glacial fluctuations of the last millennium requires documenting the spatial and temporal patterns of these glacial events. Here, we estimate the change in equilibrium line altitudes (ELAs) between the most prominent glacial advance of the last millennium and the present for four alpine glaciers located in different climatic regimes along the Andes. For each glacier, we reconstruct scenarios of climatic conditions (temperature and precipitation anomalies) that accommodate the observed ELA changes. We focus on the following glaciers: an alpine glacier in the Cordillera Vilcanota (13°S), Tapado glacier (30°S), Cipreses glacier (34°S), and Tranquilo glacier (47°S). Our results show that the range of possible temperature and precipitation anomalies that accommodate the observed ELA changes overlap significantly at three of the four sites (i.e. Vilcanota, Cipreses, and Tranquilo). Only Tapado glacier exhibits a set of climate anomalies that differs from the other three sites. Assuming no change in precipitation, the estimated ELA changes require a cooling of at least 0.7°C in the Cordillera Vilcanota, 1.0°C at Tapado glacier, 0.6°C at Cipreses glacier, and 0.7°C at Tranquilo glacier. Conversely, assuming no change in temperature, the estimated ELA changes are explained by increases in precipitation exceeding 0.52 m yr–1 (64% of the annual precipitation) in the Cordillera Vilcanota, 0.31 m yr–1 (89%) at Tapado glacier, 0.22 m yr–1 (27%) at Cipreses glacier, and 0.3 m yr–1 (27%) at Tranquilo glacier. By mapping the ELA changes and modeling the potential climate forcing across diverse climate settings, we aim to contribute toward documenting the spatial variability of climate conditions during the last millennium, a key step to decipher the mechanisms underlying the glacial fluctuation that occurred during this period.
We investigated the response of lake algal communities to changes in glacial meltwater from the Renland Ice Cap (Greenland) through the Holocene to assess whether influxes always elicit consistent responses or novel responses. We measured sedimentary algal pigments in two proximal lakes, snow-fed Raven and glacier- and snow-fed Bunny Lake, and diatom community structure and turnover in Bunny Lake. Diatom data were not available in Raven Lake. We also modeled lake-level change in Bunny Lake to identify how glacial meltwater may have altered diatom habitat availability through time. Through a series of glacier advances and retreats over the Holocene, the algal response in Bunny Lake was relatively constant until approximately 1015 yr BP, after which there were major changes in sedimentary algal remains. Algal pigment concentrations sharply declined, and diatom species richness increased. Diatom community structure underwent three reorganizations. Until 1015 yr BP, assemblages were dominated by Pinnularia braunii and Aulacoseira pffaffiana. However, approximately 1015–480 yr BP, these species declined and Tabellaria flocculosa and Hannaea arcus became a significant component of the assemblage. Approximately 440 yr BP, A. pfaffiana increased along with species indicating elevated nitrogen. In contrast, the algal pigment records from nearby snow-fed Raven Lake showed different and minimal change through time. Our results suggest that changes in the magnitude and composition of meltwater in our two study lakes were unique over the last 1000 yr BP and elicited a non-linear threshold response absent during other periods of glacier advance and retreat. Deciphering the degree to which glaciers structure algal communities over time has strong implications for lakes as glaciers continue to recede.
Land snails recovered from archeological deposits may be used to deduce climatic conditions during prehistoric occupation because their aragonitic skeletons are usually well-preserved and document valuable climatic information in the form of isotope codes. Since the snail Sphincterochila candidissima is common in archeological sites along the western Mediterranean but has been minimally investigated, the present work examines the relationship between the oxygen (18O) and carbon (13C) stable isotopes of modern specimens and relevant meteorological data. Individuals of Sphincterochila were regularly live-collected throughout 1 year (from September 2013 to October 2014) in Tarragona, NE Spain, and the 18O and 13C values were measured at the shell lip or aperture, which depicts the last growth episode closest to specimens’ collection date. Shell margin 18O values varied from +3.1 in September to –0.8 in April. Average shell margin 18O values per collection date positively correlated with monthly averaged rainwater 18O, and negatively correlated with monthly averaged maximum relative humidity, while other variables (i.e. temperature and precipitation amount) did not explain monthly–submonthly isotopic variations in the shell lip. Shell margin 13C values ranged from –11 in September to –4.8 in March, pointing to detectable variations in snails’ diet between seasons. Interestingly, snail body size positively correlated with shell margin 18O and 13C values, suggesting that larger snail size is reached under drier conditions. This work shows that S. candidissima from the western Mediterranean is a valid paleoprecipitation 18O and/or paleohumidity proxy in the region at the monthly–submonthly scale. Although shell margin 18O recorded fall and spring climate conditions only, limiting therefore their use to estimate the season of harvest, snails that grow year-round (e.g. at subtropical–tropical regions) may be used usefully for such analyses.
The contemporary role of mires in carbon exchange with the atmosphere is intensely debated. Thus, understanding the variation in Holocene peat accumulation is particularly important. We investigated carbon (C) and nitrogen (N) accumulation rates and their potential controls during the Holocene at the oligotrophic fen Degerö Stormyr (64°11'N, 19°33'E, 270 m a.s.l.), Sweden. The peat stratigraphy was dominated by remains of Eriophorum spp. and oligotrophic–mesotrophic Sphagnum spp. The long-term rate of C accumulation (LORCA) was 13.7 ± 5.5 (SD) g C m–2 yr–1, while the long-term rate of N accumulation (LORNA) was 0.28 ± 0.14 (SD) g N m–2 yr–1. Carbon and N accumulation rates exhibited similar variations that coincided with major changes in botanical composition. The botanical composition of the peat also had a major impact on the percentage of amorphous peat (a proxy for degree of decomposition). Bulk 13C values increased with decreasing C content, which probably reflected the relative increase of 13C depleted compounds in the peat during decomposition. Different plant groups exhibited different relationships, likely due to different 13C signatures of initial litters from Eriophorum spp. and Sphagnum spp. The 15N values increased significantly with decreasing C:N ratio in bulk peat, likely reflecting preferential uptake of 14N by plants concomitant with nitrogen mineralization. Here, we demonstrate the importance of botanical composition in affecting C and N accumulation rates under a changing climate and suggest that primary production drives the variation in rates of accumulation. Furthermore, we point out the importance of including 13C and 15N signatures in the analysis of peat stratigraphies to advance interpretation of Holocene peat growth and decay.
High-mountain lakes are suitable ecosystems for studying local environmental shifts driven by large-scale climate changes, with potential applications to predict future scenarios. The precise features in the response of species assemblages are not fully understood, and human pressure may often hide climatic signals. To investigate the origin and impact of past environmental changes in high-mountain ecosystems and apply this palaeoecological knowledge to anticipate future changes, we performed a multi-proxy study of a sediment core from Bassa Nera, a pond located close to montane–subalpine ecotone in the southern central Pyrenees. Combining pollen and diatom analysis at multidecadal resolution, we inferred vegetation shifts and peat bog development during the past millennium. We introduced a montane pollen ratio as a new palaeoecological indicator of altitudinal shifts in vegetation. Our results emphasize the sensitivity of the montane ratio to detect upward migrations of deciduous forest and the presence of the montane belt close to Bassa Nera pond during the Medieval Climate Anomaly. Changes in aquatic taxa allowed to date the onset of the surrounding peat bog which appeared and infilled the coring site around AD 1565. Overall, our results suggest a low-intensity human pressure and changes in management of natural resources during the last millennium, where farming was the main activity from the Medieval Climate Anomaly until AD 1500. Afterwards, people turned to highland livestock raising coinciding with the ‘Little Ice Age’.
The construction of accurate age–depth relationships and a realistic assessment of their uncertainties is one of the fundamental prerequisites for comparing and correlating late Quaternary stratigraphical proxy records. Four widely used age–depth modelling routines – CLAM, OxCal, Bacon and Bchron – were tested using radiocarbon dates simulated from varved sediment stratigraphies. All methods produce mean age–depth models that are close to the true varve age, but the uncertainty estimation differs considerably among models. Age uncertainties are usually underestimated by CLAM, whereas age uncertainties produced by Bchron are often too large. With OxCal and Bacon, the setting of model-specific parameters influences the estimated uncertainties, which vary from too large to too small. The variability of sediment accumulation rates is underestimated by CLAM but overestimated by Bacon and Bchron. Bayesian age–depth models mainly improve the assessment of uncertainties of age–depth models.
This study provides the first decadally resolved chironomid and organic geochemistry record of the Irish Neolithic from a small lake adjacent to the Carrowkeel-Keshcorran complex in County Sligo, Ireland. Chironomid (non-biting midge fly) sub-fossils and lake sediment geochemistry (13C, 15N and C:N) from the Templevanny Lough core were used to assess the timing and magnitude of within-lake responses to Neolithic farming activity. When compared with decadally resolved pollen and macroscopic charcoal records from the same core, the limnological data show a direct influence of prehistoric farming on a freshwater lake system through nutrient loading and lake eutrophication. Elevated nutrient levels, suggesting a more productive lake system, and a subsequent turnover in the chironomid community indicate a period of intensive farming activity from c. 3790–3620 BC in the early Neolithic. This was followed by a decline in farming with short periods of small-scale human activity, exemplified through nutrient loading and short-lived increases in eutrophic chironomid taxa during the middle to late Neolithic. A return of farming activity can be seen in all proxy data in the late Neolithic (c. 2720–2480 BC). The chironomid community composition typically lagged land-use change by c. 10–20 years and exhibited predictable and proportional responses to agricultural activity. The timing and magnitude of limnological changes show that land-use, rather than climate, is the main control on chironomids at Templevanny Lough, thus showing the potential prominence of the anthropogenic signal during the Neolithic.
Major changes in the Holocene were identified based on a diatom and geochemical analysis of sediment cores from Lakes Ufimskoe and Syrytkul (the Southern Urals). The Lake Ufimskoe ecosystem in the Central mountain area is identified to be highly sensitive to variations in temperature. Meanwhile, Lake Syrytkul is more responsive to climate aridization because of its limnological characteristics and less precipitation in the piedmont area. Climate events were the main drivers for lake ecosystems dynamics throughout almost the whole history of the lakes. The records of lake sediments reflect several climate events noted elsewhere in the Northern Hemisphere: Lateglacial–Holocene transition (~12,000–11,600), Preboreal oscillation (~11,200–11,000 cal. BP), climate warming and aridization (~9700–9600 cal. BP), warming and increase in precipitation since 9000 cal. BP, climate aridization at ~5800 cal. BP, cooling since 4000 cal. BP, and warming at ~2500 cal. BP. Climate warming of the last hundred years was not reflected in lake sediment records because of the significant human impact on the lake ecosystem. The upper sediments of both lakes are enriched in As, Bi, Sb, Te, Sn, Cd, Cu, Zn and Pb because of the influence of the Karabash copper smelter. However, the significant changes of the Lake Syrytkul ecosystem are not related to the technogenic impact and explained mainly by the dam construction. The changes in diatom communities identified in Lake Ufimskoe, which is located in an area geologically sensitive to acidification, are related to the acidification and heavy metal loading on the water area.
Paleoenvironmental studies previously performed on Lake Igaliku revealed two agropastoral phases in south Greenland: the Norse settlement from AD 986 to ca. AD 1450 and the recent installation of sheep farmers, since the 1920s. To improve the knowledge of the timing and magnitude of the Greenlandic agropastoral activities, a lipid inventory was realized and compared with biological and geochemical data. During the 12th century, a major increase in deoxycholic acid (DOC) and coprophilous fungal spores revealed a maximum of herbivores. Synchronously, a minimum of the n-C29/n-C31 alkane ratio and tree and shrub pollen and a maximum of triterpenyl acetates showed a reduction in the tree and shrub cover, because of grazing activities. Lupanone, produced by angiosperms, appeared simultaneously in the molecular content, probably revealing an introduction of plant species by the Norse, as it has been the case for Rumex spp. No major erosion was recorded by trimethyl-tetrahydrocrysenes (TTHCs) and titanium (Ti) fluxes. No massive algal production, identified by the n-C17/total n-alkane ratio and mesotrophic diatoms, was either revealed. After the Norse abandon (around AD 1450), a return of the vegetation to quasi-pristine conditions was observed in the molecular content. Finally, a re-introduction of sheep in the 1920s provoked major impacts between the 1970s and the 1990s. A major decrease in the n-C29/n-C31 alkane ratio and tree and shrub pollen associated with maxima of triterpenyl acetates, TTHCs, Ti fluxes, and mesotrophic diatoms highlighted a reduction in the tree and shrub cover, a strong soil mobilization, and algal blooms, probably linking to the recent mechanized creation of hay fields and the massive use of fertilizers. In this study, molecular biomarkers revealed two periods of major impacts: the 12th century and between the 1970s and the 1990s, separated by centuries without agropastoral practices, allowing a quasi-resilience of the vegetation.
The eastern levee of the Active Channel in the Bengal fan has been investigated in order to better understand the history of turbidite activity in this channel during the Holocene in the context of Ganges-Brahmaputra ‘source-to-sink’ system. A robust 14C-based chronostratigraphy provides high temporal resolution for reconstructing sediment accumulation history on the eastern levee of the Active Channel. Integration of this study with previous work in the area suggests that the Bengal fan has remained continually connected with the Ganges-Brahmaputra fluvial system through the Holocene, feeding through the main canyon, the Swatch of No Ground (SoNG). An intense turbidite activity occurred during a transgressive wet period from 14.5 to 9.2 ka cal. BP, followed by an abrupt shift in sedimentation at 9.2 ka cal. BP, probably due to the high sea level leading to a partial disconnection between massive river discharges and the deep turbidite system. During the last 9.2 ka cal. BP, turbidite activity is still present but irregular, likely modulated by a combination of various forcings such as monsoon variability and river migration. In total, three phases are distinguishable during this period: 9.2–5.5, 5.5–4, and 4 ka cal. BP to modern, according to the turbidite record. Unexpectedly, the Indo-Asian monsoon does not appear to be the only predominant forcing on the establishment of the Bengal fan during the Holocene because of the combination of different forcings directly affecting transfers between the Ganges-Brahmaputra and the Bengal fan as well as river migrations, delta construction, and potentially anthropogenic impact.
In order to improve the reliability of climate models in their projections for the future, spatially and temporally detailed paleoclimate proxy data are needed. In this study, we examined annually laminated sediments from Lake Nurmijärvi (Finland) for their fossil Chironomidae assemblages over a time period with available meteorological observational data (since 1830s). In doing so, we correlated chironomid-based inferences of summer air temperatures against instrumentally measured values using two different reconstruction approaches, namely, calibration-in-space (CiS, multilake training set) and calibration-in-time (CiT, calibration of time series data against meteorological data). The results showed that the principal variability in fossil chironomid assemblages in the sediment core corresponded to the measured air temperatures. In addition, the temperatures reconstructed using CiS (R = 0.38, p = 0.014) and CiT (R = 0.51, p = 0.001) correlated significantly with the meteorological data; however, the CiS approach showed higher variability and larger differences against the instrumentally measured values. A significant lag of on average 4–8 years was also found in the chironomid response to observed temperature change that is, nevertheless, much shorter time span than with some other paleoclimate proxies. The results verify the usability and sensitivity of chironomids as a paleoclimate proxy in the Nurmijärvi varved sediment record with the potential value of an exceptionally well-resolved downcore record of the Holocene climate change in the future. The CiT approach can potentially provide accurate paleotemperature estimates at the late-Holocene scale, but the CiS approach may be more useful at longer timescales if the community compositions change significantly from those occurring during the calibration period of the CiT.
To elucidate the natural variability of Atlantic and Coastal water, a late-Holocene multi-proxy analysis is performed on a marine sediment core from the northern Norwegian margin. This includes planktic foraminiferal fauna and their preservation indicators, stable isotopes (18Oc, 13C), sub-surface temperature (SSTMg/Ca) and salinity (SSS) records based on paired Mg/Ca and 18Oc measurements of Neogloboquadrina pachyderma and transfer function–derived sub-surface temperatures (SSTTransfer). The record shows a general cooling with subtle fluctuating palaeoceanographic conditions, here attributed to shifting North Atlantic Oscillation (NAO) modes. Period I (ca. 3500–2900 cal. yr BP) is strongly influenced by Coastal water and stratified water masses, possibly correlating to negative NAO conditions. During period II (ca. 2900–1600 cal. yr BP), dominating warm Atlantic water might be linked to a positive NAO mode and the Roman Warm Period. A renewed influence of Coastal water is observed throughout period III (ca. 1600–900 cal. yr BP). Stable and colder SST values potentially correlate to the Dark Ages and are here attributed to negative NAO conditions. Within period IV (ca. 900–550 cal. yr BP), the core site experienced a stronger influence of Atlantic water which might be because of the positive NAO conditions correlating to the ‘Medieval Warm Period’. Additionally, an inverse correlation in Atlantic water influence between the eastern and western Atlantic Ocean is observed throughout periods II, III and IV. This Atlantic oceanographic see-saw pattern is attributed to an opposite climatic response to changing NAO conditions arguing for a coupling between ocean and atmosphere.
Palaeoecological evidence is used to investigate climatic and anthropogenic drivers of vegetation and fire dynamics through the past ~1200 years in the Eastern Arc Mountains, Tanzania. Pollen and charcoal analyses are supported by a chronology derived from five accelerator mass spectrometry ages, a 137Cs activity profile and marker horizons from two exotic pollen taxa. Pollen indicator taxa are used to develop a series of environmental indices, and compared with fluctuations in key timber species, and a fire history reconstruction. Prior to AD 1274, the ecosystem is characterised by moist montane forest that is somewhat anomalous with other East African records, providing evidence for the persistence of a mesic environment and ecosystem resilience of the Eastern Arc Mountains. An open drier forest type is recorded from AD 1275 to 1512, resulting from regional aridity; when the aforementioned buffering ability was exceeded and ecosystem resilience curtailed. Maize appears from ~AD 1737, possibly associated with the regional expansion of agriculture to supply the ivory trade. The peak of the caravan trade in the mid-19th century, and later colonial administration, coincides with intensified human impacts, specifically forest clearance suggested by substantial declines in the timber tree Ocotea. Following independence, there are tentative signals of montane forest recovery, which coincide with the establishment of forest reserves, and associated timber bans. Palaeoecological understanding of historical ecosystem change in the Eastern Arc Mountains biodiversity hotspot is vital to build informed conservation and forest management policies for a future characterised by growing human populations coupled with changing climate–ecosystem relationships.
A cal. 20-year-resolution pollen record from Gonghai Lake presented the detailed process of mountain vegetation succession and East Asian Summer Monsoon (EASM) changes since the last deglaciation in Shanxi Province, North China. Modern vegetation distribution and lake surface pollen assemblages suggested that the fossil pollen mainly came from local and surrounding vegetation in Gonghai Lake, which reflected the elevational changes of plant communities in study area. From 14,700 to 11,100 cal. yr BP, open forests and mountain meadows dominated by shrubs and herbaceous species in surrounding area, suggesting a weak EASM with less precipitation. In the period between 11,100 and 7300 cal. yr BP, bushwoods and grasses were gradually replaced by mixed broadleaf-conifer forest, first developed by pioneer species of Betula and Populus and then replaced by Picea, Pinus, and Quercus, implying an enhanced EASM and increased temperature and precipitation. During the period of 7300–5000 cal. yr BP, warm-fitted trees became expanded and widespread, indicating a climax community of mixed broadleaf-conifer forest and warm and humid climate with higher temperature and sufficient precipitation and the strongest period of EASM. From 5000 to 1600 cal. yr BP, Pinus pollen increased, but Quercus pollen decreased, showing the breakup of the climax community and the recession of the EASM. Since 1600 cal. yr BP, under the threats of land reclamation and deforestation, forest cover sharply decreased, and mountain grass lands were developed. The EASM changes inferred from pollen record of Gonghai Lake were asynchronous to the oxygen isotope records of stalagmites from southern China. We suggest that the existence of remnant Northern Hemisphere ice sheets and relative low sea levels might hampered the northward penetration of the EASM in early Holocene, which caused the maximum monsoon precipitation to reach northern China until mid-Holocene.
This is a detailed tephrostratigraphical investigation of late Quaternary deposits in the Longgang and Changbaishan Volcanic Fields of northeastern China. A total of 45 reference samples which were collected from either side of the Chinese/Korean border showed very similar geochemical characteristics to the Millennium eruption of Tianchi Volcano. Through comparing the published data of the glass shards detected in Gushantun with these reference samples, further description is that the glass shards in the sediment of Gushantun came from the Tianchi Volcano eruption in AD 1702, 1668, and 1597. A basaltic tephra layer found in the sediment of Hanlongwan associated with an eruption of the Jinlongdingzi Volcano which happened in 1500–2100 cal. yr BP by comparing with the published data from Sihailongwan and Xiaolongwan. Tianchi and Jinlongdingzi Volcano are both active and erupted several times during the historical period. Reference samples and the tephra layers detected in Hanlongwan, Sihailongwan, Gushantun, Erlongwan, and Xiaolongwan can be used as marker horizons beyond the Longgang Volcanic Field and Changbaishan Volcanic Field, including, for example, in Japan, Korea, nearby coastal area of Russia, and marine records.
When the Laurentide ice sheet retreated rapidly (~150 m/a) across the Penobscot Lowland between ~16 and ~15 ka, the area was isostatically depressed and became inundated by the sea. Silt and clay were deposited, but no significant moraines or deltas were formed. The Penobscot River was reborn at ~14 ka when ice retreated onto land in the upper reaches of the river’s East Branch. As isostatic rebound exceeded sea level rise from melting ice, the river extended itself southward. Between ~13.4 and 12.8 ka, it established a course across marine clay and underlying glacial till in the Lowland. Its gradient was low as differential rebound had not begun. Discharge, however, was higher and the river transported and deposited outwash gravel. During the cold, dry Younger Dryas, ~11 ka, eolian sand began to accumulate in dunes in the Lowland. Some of this sand, along with fluvial sediment from the headwaters, was redistributed into terraces along gentler stretches of the river and into a paleodelta in Penobscot Bay. Eolian activity continued to ~8 ka and aggradation in terraces until ~6 ka. The climate became wetter and warmer after ~6 ka, the dunes were stabilized by vegetation, the river began to downcut, and braiding became less intense. Pauses in the downcutting are reflected in discontinuous strath terraces. In due course, the river re-encountered the old outwash gravels, marine clay, glacial till, and, in a few places, bedrock. Its profile is now stepped, with gentle, gravel-bedded reaches between bedrock ribs that form rapids.
Several important North American coastal conifers – having immigrated during the Holocene from the southeast – reach their northern and upper elevation limits in south-central Alaska. However, our understanding of the specific timing of migration has been incomplete. Here, we use two new pollen profiles from a coastal and a high-elevation site in the Eastern Kenai Peninsula–Prince William Sound region, along with other published pollen records, to investigate the Holocene biogeography and development history of the modern coastal Picea (spruce)–Tsuga (hemlock) forest. Tsuga mertensiana became established at Mica Lake (100 m elevation, near Prince William Sound) by 6000 cal. BP and at Goat Lake (550 m elevation in the Kenai Mountains) sometime after 3000 years ago. Tsuga heterophylla was the last major conifer to arrive in the region. Although driven partially by climate change, major vegetation changes during much of the Holocene are difficult to interpret exclusively in terms of climate, with periods of slow migration alternating with more rapid movement. T. mertensiana expanded slowly northeastward in the early Holocene, compared with Picea sitchensis or T. heterophylla. Difficulty of invading an already established conifer forest may account for this. We suggest that during the early Holocene, non-climatic factors as well as proximity to refugia, influenced rates of migration. Climate may have been more important after ~2600 cal. BP. Continued expansion of T. mertensiana at Goat Lake at the Medieval Climate Anomaly (MCA)–‘Little Ice Age’ (‘LIA’) transition suggests warm and wet winters. But expansion of T. mertensiana at both sites was arrested during the colder climate of the ‘LIA’. The decline was more extensive at Goat Lake, where climatic conditions may have been severe enough to reduce or eliminate the T. mertensiana population. T. mertensiana continued its expansion around Goat Lake after the ‘LIA’.
The Bigstick and Seward Sand Hills are possibly two of the oldest dune fields within the late Wisconsin glaciated regions of the Northern Great Plains. As with most Northern Great Plains dune fields, source sediments are former proglacial outwash sands. Thus, Holocene dune construction is primarily related to spatial–temporal variations in surface cover and transport capacity, rather than renewed sediment input. However, eolian landscape reconstructions on the Northern Great Plains have been temporally constrained to recent periods of activity, as older episodes of deposition are typically reworked by younger events. In this study, sediment cores from shallow lacustrine basins and interdune areas provide an improved record of Holocene eolian sand deposition. Eolian sand accumulation in the interdunes and basins occurred between 150 and 270 years ago, 1.9 and 3.0 ka, 5.4 and 8.6 ka, and prior to ca. 10.8 ka. These episodes of sand accumulation were bracketed by lacustrine deposition and soil formation, which represented wetter conditions. Other than mid-Holocene dune activity, which may be related to peak warmth and aridity, most periods of eolian sand accumulation coincided with cooler but drier climatic events such as the Younger Dryas, late-Holocene cooling prior to the Medieval Climatic Anomaly, and the ‘Little Ice Age’. These depositional episodes are also spatially represented by other dune fields in the region, providing a broad-scale view of the connections between past climatic events and eolian landscape evolution on the Northern Great Plains.
Wetlands are very vulnerable ecosystems and sensitive to changes in the ground water table. For the last few thousand years, hydrological balance has also been influenced by human activity. To improve their cropping features, drainage activity and fertilizing were applied. The drainage process led to an abrupt change of environment, the replacement of plant communities and the entire ecosystem. The problem of carbon sequestration is very important nowadays. A higher accumulation rate is related to higher carbon accumulation, but the intensity of carbon sequestration depends on the type of mire, habitat, and climatic zone. The main aim of this article was an examination of the changes in poor-fen ecosystem during the last 200 years in relation to natural and anthropogenic factors, using paleoecological methods (pollen and macrofossils). The second aim was a detailed investigation of the sedimentary record to aid our understanding of carbon sequestration in the poor fen of temperate zone. This case study shows that fens in temperate zones, in comparison with boreal ones, show higher carbon accumulation rates which have been especially intensive over the last few decades. To reconstruct vegetation changes, detailed palynological and macrofossil analyses were done. A 200-year history of the mire revealed that it was influenced by human activity to much degree. However, despite the nearby settlement and building of the drainage ditch, the precious species and plant communities still occur.
Near-annual pollen records for the last 100 years were obtained from a 65-cm peat monolith from a raised peat bog in the Central Forest State Natural Biosphere Reserve (southern part of the Valdai Hills, European Russia) and compared with the available long-term meteorological observations. An age–depth model for the peat monolith was constructed by 210Pb and 137Cs dating. Cross-correlation and the Granger causality analysis indicated a broad range of statistically significant correlations between the pollen accumulation rate (PAR) of the main forest-forming trees and shrubs (Picea, Pinus, Betula, Tilia, Quercus, Ulmus, Alnus, and Corylus) and the air temperature and precipitation during the previous 3 years. Results showed that high air temperatures during the growing season (May–September) in the year prior to the flowering led to an increase in pollen productivity of the main tree species. The statistically significant correlation between the PAR of trees and shrubs and winter precipitation of the current and previous years could reflect the influence of winter precipitation on soil water availability and as a result on tree growth and functioning in the spring.
Two gravity cores (778 and 780) sampled at the Nelson River mouth and one (776) at the Churchill River mouth in western Hudson Bay, Canada, were analyzed in order to identify the impact of dam construction on hydrology and sedimentary regime of both rivers. Another core (772) was sampled offshore and used as a reference core without a direct river influence. Core chronology was established using 14C and 210Pb measurements. Cores 778 and 780 show greater variability than the others, and the physical, chemical, magnetic, and sedimentological properties measured on these cores reveal the presence of several hyperpycnites, indicating the occurrence of hyperpycnal flows associated with floods of the Nelson River. These hyperpycnal flows were probably caused by ice-jam formation, which can increase both the flow and the sediment concentration following the breaching of such natural dams. However, these hyperpycnites are only observed in the lower parts of cores 778 and 780. It was not possible to establish a precise chronology because of the remobilization of sediments by the floods. Nevertheless, some modern 14C ages suggest that this change in sedimentary regime is recent and could be concurrent with the dam construction on the Nelson River, which allows a continuous control of its flow since the 1960s. This control prevented the formation of hyperpycnal flows and the deposition of hyperpycnites. Finally, core 776 contains only one rapidly deposited layer. This lower frequency may be related to the enclosed estuary of the Churchill River, its weaker discharge, and the distance of the site from shore.
Minerotrophic fens and ombrotrophic bogs differ in their nutrient status, hydrology, vegetation and carbon dynamics, and their geographical distribution is linked to various climate parameters. Currently, bogs dominate the northern temperate and southern boreal zones but climate warming may cause a northwards shift in the distribution of the bog zone. To more profoundly understand the sensitivity of peatlands to changes in climate, we first used the plant macrofossil method to identify plant communities that are characteristic of past fen–bog transitions. These transitions were radiocarbon dated, to be linked to Holocene climate phases. Subsequently, palaeoecological data were combined with an extensive vegetation survey dataset collected along the current fen–bog ecotone in Finland where we studied how the distribution of the key plant species identified from peat records is currently related to the most important environmental variables. The fossil plant records revealed clear successional phases: an initial Carex-dominated fen phase, an Eriophorum vaginatum–dominated oligotrophic fen phase followed by an early bog phase with wet bog Sphagna. This was occasionally followed by a dry ombrotrophic bog phase. Timing of initiation and phase transitions, and duration of succession phases varied between three sites studied. However, the final ombrotrophication occurred during 2000–3000 cal. BP corresponding to the neoglacial cooling phase. Dry mid-Holocene seems to have facilitated initiation of Eriophorum fens. The peatlands surveyed in the fen–bog ecotone were classified into succession phases based on the key species distribution. In 33% of the studied peatlands, Sphagnum had taken over and we interpret they are going through a final transition from fen to bog. In addition to autogenic processes and direct climate impact, our results showed that ecosystem shifts are also driven by allogenic disturbances, such as fires, suggesting that climate change can indirectly assist the ombrotrophication process in the southern border of the fen–bog ecotone.
Central Asia is located at the confluence of large-scale atmospheric circulation systems. However, the number of Holocene climate records is still low in most parts of this region and insufficient to allow detailed discussion and comparisons to disentangle the complex climate history and interplays between the different climatic systems. Here, we present the first stalagmite record from arid Central Asia (south-western Kyrgyzstan) by using 18O, 13C, and micro x-ray fluorescence (µXRF)-sulfur data spanning the last 5000 years. The cave hosting stalagmite Uluu-2 is ideally suited to identify past shifts in seasonal variations in precipitation in this part of the world. Comparison of instrumental and paleo-isotopic studies demonstrates that the Uluu-2 speleothem isotope composition faithfully records climate changes and responds to shifts in the proportion of moisture derived from mid-latitude Westerlies during the winter/spring season. The reconstructions suggest that the area was characterized by a dry climate from 4700 to 3900 yr BP, interrupted by a wet episode around 4200 yr BP. Further drier conditions also occurred between 4000 and 3500 yr BP. Wetter conditions were re-established at ca. 2500 yr BP, after another dry episode between 3000 and 2500 yr BP. With the exception of two short dry events (1150 and 1300 yr BP), the period after 1700 yr BP shows moderate to wet conditions. Regional comparisons suggest that the strength and position of the Westerly winds control climatic shifts in arid Central Asia, leading to complex local responses.
The location of the Altai Mountains at the limits of both the Pacific and Atlantic influences implies that this mountain range is an important climatic boundary. Based on pollen data of 188 samples of a 390-cm core from Narenxia Peat in the southern Altai with a chronologic support of 11 accelerator mass spectrometry (AMS) dates, we reconstructed the Holocene climatic change at Narenxia Peat. The reconstruction revealed five stages of climatic change: a cold and dry latest deglacial (prior to ~11,500 cal. yr BP), a warm and wet early-Holocene (~11,500 to ~7000 cal. yr BP), a considerably cooled and dried middle Holocene (~7000 to ~4000 cal. yr BP), a resumed warm and wet late-Holocene (~4000 to ~1200 cal. yr BP), and a relatively cool and dry latest Holocene (past ~1200 years). The reconstructions of mean annual temperature (MAT) and mean annual precipitation (MAP) from Narenxia Peat well resemble the reconstructions of North Atlantic Oscillations (NAO) and El Niño–Southern Oscillations (ENSO). The resemblance implies that the Holocene millennial-scale changes in MAT and MAP in the Altai might have been causally associated with the variations in NAO and ENSO.
The timing of lake-level fluctuations on the Tibetan Plateau and their relationship with climatic changes is still under debate, and the main reason for this is the lack of suitable archives for reconstructing the paleohydrology and paleoclimatology of the lakes. Here, we present the results of analyses of the shell geochemistry of Radix sp. from an exposed terrace of Nam Co lake on the south-central Tibetan Plateau. Optically stimulated luminescence (OSL) dating reveals that deep-water lacustrine sediments formed between ca. 4.4 and 2.2 ka, suggesting a high and stable lake level significantly above the present. The results of Sr/Ca, 13C and 18O analyses of the fossil shells of Radix sp. indicate that during the mid- to late-Holocene, lake-level variations in Nam Co were mainly controlled by variations in the Indian Summer Monsoon. A trend of decreasing evaporation also played an important role. Comparison with other results suggests a consistent pattern of mid- to late-Holocene lake-level changes across a large area of the Tibetan Plateau and adjacent regions to the south, which had a similar causal mechanism. Finally, our results indicate that fossil shells of the gastropod Radix sp. of the lakes on the Tibetan Plateau are a valuable archive for reconstructing the regional paleohydrology and paleoclimatology.
The early- and mid-Holocene deposits of the Lower Khuzestan plain at the north-eastern margin of the Persian Gulf have been investigated by means of facies analysis of sediment successions of undisturbed cores. Organic material and molluscs have been selected for dating by radiocarbon whereby possible contamination by hard-water effect is discussed. The results suggest that the Holocene transgression in Mesopotamia may have taken place later than generally accepted. Before ca. 7700–7900 yr cal. BP, the plain was characterized by mud-dominated fluvial systems. During the mid-Holocene, tides invaded the existing valleys, and the sedimentary environment shifted from fluvial to estuarine but not as extensively as has previously been suggested. The estuarine environments lasted for about 2000–2500 years until ca. 4850–5000 yr cal. BP when the seaward part of the plain was again characterized by widespread fluvial sedimentation.
The eastern Lesotho Highlands experience climate patterns distinct from those of surrounding lower altitude regions, representing a niche environment with a unique biodiversity, leading to well-adapted but restricted vegetation. This study explores changes in the Holocene composition of diatoms and pollen at southern Africa’s highest altitude wetland (Mafadi: 3390 m a.s.l.). The palaeoenvironmental record for Mafadi Wetland indicates fluctuations between cold, wet conditions, prevalent between ~8140 and 7580 cal. yr BP and between ~5500 and 1100 cal. yr BP, and warmer, drier periods between ~7520 and 6680 cal. yr BP and between ~6160 and 5700 cal. yr BP. Marked climatic variability is noted from ~1100 cal. yr BP with colder conditions at ~150 kyr BP. Notably, the first of these cold periods occurs soon after the Northern Hemisphere 8.2 kyr event, while a second period of notably cold conditions occurs around 1100 cal. yr BP. Variability exists between the moisture reconstructions presented in this study and those from adjacent lower altitude sites, which is hypothesised to reflect variations in the strength and extent of the Westerlies throughout the Holocene.
Here, we present high-resolution trace element and stable isotope records from three coeval Holocene stalagmites from the Herbstlabyrinth cave system, Central Germany. All stalagmites were precisely dated using MC-ICPMS 230Th/U-dating. One stalagmite started to grow at 13.62 ± 0.13 ka BP, covering the late Glacial; the other two speleothems started to grow at 11.13 ± 0.08 and 10.26 ± 0.08 ka BP, respectively. The combined record covers the entire Holocene. The interpretation of the different climate proxies is supported by data from a detailed cave monitoring programme. Cold conditions during the Younger Dryas are reflected by intermittent stalagmite growth at the Herbstlabyrinth. The 18O records are in general agreement with the NGRIP 18O record on millennial time scales indicating that speleothem 18O values at the Herbstlabyrinth reflect large-scale climate variability in the North Atlantic area. The 8.2 ka event is clearly visible as a pronounced negative excursion in the 18O records. In all other proxies, it is not reflected as a major excursion. Correlation and principal component analysis enable us to disentangle the various processes affecting the stable isotope and trace element signals. Phases with higher P, Ba and U concentrations and more negative 13C values are interpreted as reflecting more productive vegetation above the cave. The negative correlation of Mg with P, Ba and U and the positive correlation with 13C indicate more recharge during phases of more productive vegetation, probably because of increased rainfall. The majority of the observed phases of reduced vegetation productivity and drier climate coincide with cooler periods in the polar North Atlantic as reflected by a higher abundance of hematite-stained grains (i.e. the Bond events), suggesting a close relationship between terrestrial climate in Central Europe and the polar North Atlantic.
The South Wellesley Islands in the Gulf of Carpentaria, northern Australia, were the recent focus of a palynological investigation which found vegetation change during the Holocene was driven by coastal progradation and regional climate. Here, we present new elemental data from x-ray fluorescence core scanning which provides non-destructive, continuous and high resolution analysis from three wetlands across Bentinck Island, the largest of the South Wellesley Islands. Elemental data and grain size analyses are combined with lead-210 (210Pb) and accelerator mass spectrometry (AMS) carbon-14 (14C) dates. An open coastal environment was present 1250 cal. a BP on the south east coast of Bentinck Island, with sediment supply incorporating fluvial deposition and detrital input of titanium and iron from eroding lateritic bedrock. Prograding shorelines, dune development and river diversion formed a series of swales parallel to the coast by ~800 cal. a BP, forming the Marralda wetlands. Wetlands developed at sites on the north and west coasts ~500 and ~450 cal. a BP, respectively. Geochemical and grain size analyses indicate that wetlands formed as accreting tidal mudflats or within inter-dune swales that intercepted groundwater draining to the coastal margins. The timing of wetland initiation indicates localised late-Holocene sea level regression, stabilisation and coastal plain development in the Gulf of Carpentaria. Elemental data provide new records of wetland development across Bentinck Island, highlighting the value of a multi-proxy approach to understanding environmental change during the Holocene in tropical northern Australia.
Anthracological analysis was carried out in the archaeological site of Punta di Zambrone on the Tyrrhenian coast of Calabria in southern Italy. Archaeological excavation documented at the site settlement deposits dated mainly to Early Bronze Age (EBA, 21st–18th century BC) and the Recent Bronze Age (RBA, 13th to early 12th century BC). In the phase of the EBA village, the high frequency of Olea europaea in the charcoal data suggests the tree may well have been cultivated by favouring the spread of the scant olive trees growing wild. Comparison with existing archaeobotanical data indicates that olive cultivation spread over a large portion of southern Italy from the EBA and the early Middle Bronze Age (MBA, 17th–15th century BC), thus calling into question the hypothesis of its first cultivation related to the interaction between Mycenaean Greece and local cultures in southern Italy. The early domestication event at Punta di Zambrone supports the idea of multiple independent primary events of olive domestication throughout the Mediterranean basin. In the following phase of the fortified settlement dated to the RBA, the frequency of olive charcoal diminished and the expansion of a more or less dense forest dominated by Quercus was judged to be a consequence of human depopulation that characterises the end of MBA and also a different land use of RBA. This forest increase, also recorded by other archaeobotanical proxies in the central and southern Italian peninsula, is found to be related to the diffusion in southern Calabria of the Subapennine culture, spreading from more northerly areas of Italy and bringing different economic systems and agronomic knowledge. These far-reaching changes appear to have brought to a halt the first event of olive cultivation recorded at Punta di Zambrone.
Sedimentological and geochemical results from Nir’pa Co, an alpine lake on the southeastern Tibetan Plateau, detail late-Holocene Indian summer monsoon (ISM) hydroclimate during the last 3300 years. Constrained by modern calibration, elevated silt and lithics and low sand and clay between 3.3 and 2.4 ka and 1.3 ka and the present indicate two pluvial phases with lake levels near their current overflow elevation. Between 2.4 and 1.3 ka, a sharp increase in sand and corresponding decrease in lithics and silt suggest drier conditions and lower lake levels at Nir’pa Co. Hydroclimate expressions in the sedimentological proxies during the Medieval Climate Anomaly (MCA) and ‘Little Ice Age’ (LIA) are not statistically significant, suggesting that these events were minor compared to the millennial scale variability on which they were superimposed. However, decreasing sand and increasing lithics and silt during the MCA between 950 and 800 cal. yr BP may suggest briefly wetter conditions, while increasing sand and reduced lithics and silt from 500 to 200 cal. yr BP suggest potentially drier conditions during the LIA. Similarities with regional records from lake sediment and ice cores and speleothem records from the central and eastern Tibetan Plateau, India, and the Arabian Sea, suggest generally coherent late-Holocene ISM variability in these regions. Increased late-Holocene ISM intensity occurred during times when Tibetan Plateau surface air temperatures were warmer, Indo-Pacific sea surface temperatures were elevated, and the tropical Pacific was in a La Niña–like mean state. Conversely, aridity between 2.4 and 1.3 ka occurred in concert with cooling on the Tibetan Plateau and in the Indo-Pacific with more El Niño–like conditions in the tropical Pacific. Differences with western Tibetan records may reflect a weakened ISM and stronger westerlies in this region during the late-Holocene.
This study of five sand units at Lavericks Bay, New Zealand, reports on the sedimentary evidence for three trans-Pacific tsunamis and two local storms. The 1868 Arica, 1877 Iquique and 1960 Valdivia tsunamis from Chile were the largest distantly generated events in New Zealand’s history but have never before been identified at the same location. It is also the first time that the 1877 Iquique tsunami deposit has been found in New Zealand. Two further sand units were identified as local storm deposits laid down in 1869/1870 and 1929. The identification and chronology of these events were established through the use of geochemistry, palynology, diatoms, charcoal abundance and historical documents. Their relative magnitudes were estimated through the use of grain size parameters and lateral extent of the recognisable sand layers. The recognisable sandy tsunami deposits extend about 60% of the inundation distance, while the storm sediments are finer and less extensive. There were two notable geochemical differences between the storm and tsunami deposits. Both storm deposits had lower concentrations of marine proxy elements associated with lower Ca–Ti and Sr–Ba ratios. Other differences were noted between some of the tsunami and storm deposits such as rip-up clasts and sediment characteristics, but these were by no means unequivocal. It is possible that geochemistry may prove to be the only proxy capable of not only differentiating effectively between storm and tsunami sediments but also identifying the maximum inland extent of a deposit and of inundation. It is the ability to better understand the nature and extent of such catastrophic events through these subtle differences in event characteristics that will help improve risk management for coastlines around the world.
The result of 344 radiocarbon-dated megafossils is here presented and discussed. This study aims at elucidating early- to mid-Holocene forest-line and climate dynamics in the southern Scandes along a present gradient of decreasing forest-line elevations. Around 9.5 calibrated ka before present (BP), pine suddenly established vertical belts of at least 200 m. These represent the highest pine-forests during the Holocene, ca. 210–170 m higher than today when corrected for land uplift. By this, summer temperatures at least 1–1.3°C warmer than today are indicated for the early Holocene thermal maximum around 8.5–9.5 cal. ka BP. The most pronounced warming occurred in Jotunheimen, the highest mountain range in Scandinavia, because of an amplified ‘Massenerhebung’ effect. Megafossils show the establishment of birch-forests above pine-forests already from the early Holocene. Pine-forests started their decline in the early Holocene and became replaced by the less warmth-demanding birch-forests. Pine megafossil results and pollen studies from the same areas show that cooling around 8.5 cal. ka BP caused a significant decrease in pine pollen production whereas pine-forest-lines were more or less unaffected. In the following period of about 2000 years, the high-altitudinal pine-forests could hardly be detected in pollen diagrams. This shows how strongly past temperatures influenced on the pollen production of individuals and how this might obscure pollen-based reconstructions of past vegetation. To be able to correct for this error, there is a need for establishing exact present-day relationships between temperature and pollen production of prolific pollen producers.
Rates of biological evolution on islands are often presumed to exceed rates on the mainland. We tested this postulation by computing the evolutionary rate of head shape in Italian wall lizard Podarcis siculus, occurring on four islands off the coast of Southern Italy. We calculated the evolutionary rate using a phylogenetic tree whose node ages were derived from Lambeck et al. predicted ages of geographic isolation of the islands. Such ages are based on a relative sea-level change model for the late Pleistocene–Holocene. Through a likelihood optimization procedure, our method allows computing, besides the evolutionary rate, biological estimates of the ages of insular populations, with this indirectly testing Lambeck et al.’s model estimates. We found that the rate of evolution in Podarcis head shapes on islands is not statistically different from the mainland rate, although insular lizards have distinctive head shapes. Overall, the insular phenotype took 1–4000 years to arise (differing among islands). The estimated ages of insular populations are lower than Lambeck et al.’s estimates and fall in the 5- to 6-ka interval.
Rapid ecosystem transitions and adverse effects on ecosystem services as responses to combined climate and human impacts are of major concern. Yet few long-term (i.e. >60 years) quantitative observational time series exist, particularly for ecosystems that have a long history of human intervention. Here, we combine three major environmental pressures (land use, nutrients and erosion) with quantitative summer and winter climate reconstructions and climate model simulations to explore the system dynamics, resilience and the role of disturbance regimes in varved eutrophic Lake Zabiłskie (NE Poland) since AD 1000. The comparison between these independent sources of information allows us to establish the coherence and points of disagreements between such data sets. We find that climate reconstructions capture noticeably natural forced climate variability, while internal variability is the dominant source of variability during most parts of the last millennium at the regional scale, precisely at which climate models seem to underestimate forced variability. Using different multivariate analyses and change point detection techniques, we identify ecosystem changes through time and shifts between rather stable states and highly variable ones. Prior to AD 1600, the lake ecosystem was characterised by high stability and resilience against observed natural climate variability. During this period, the anthropogenic fingerprint was small; the lake ecosystem was buffered against the combined human and natural disturbance. In contrast, lake–ecosystem conditions started to fluctuate across a broad range of states after AD 1600. The period AD 1745–1886 represents the phase with the strongest human disturbance of the catchment–lake ecosystem. During that time, the range of natural climate variability did not increase. Analyses of the frequency of change points in the multi-proxy data set suggest that the last 400 years were highly variable and increased vulnerability of the ecosystem to the anthropogenic disturbances. This led to significant rapid ecosystem transformations.
Northern Hemisphere cooling between 1400 and 1900 in the Common Era (CE) resulted in the expansion of glaciers during a period known as the ‘Little Ice Age’ (LIA). Early investigation of recent advances of Himalayan glaciers assumed that these events were synchronous with LIA advances identified in Europe, based on the appearance and position of moraines and without numerical age control. However, applications of Quaternary dating techniques such as terrestrial cosmogenic nuclide dating have allowed researchers to determine numerical ages for these young moraines and clarify when glacial maxima occurred. This paper reviews geochronological evidence for the last advance of glaciers in the Himalaya. The 66 ages younger than 2000 years (0–2000 CE) calculated from 138 samples collected from glacial landforms demonstrate that peak moraine building occurred between 1300 and 1600 CE, slightly earlier than the coldest period of Northern Hemisphere air temperatures. The timing of LIA advances varied spatially, likely influenced by variations in topography and meteorology across and along the mountain range. Palaeoclimate proxies indicate cooling air temperatures from 1300 CE leading to a southward shift in the Asian monsoon, increased Westerly winter precipitation and generally wetter conditions across the range around 1400 and 1800 CE. The last advance of glaciers in the Himalaya during a period of variable climate resulted from cold Northern Hemisphere air temperatures and was sustained by increased snowfall as atmospheric circulation reorganised in response to cooling during the LIA.
Dates for early cultivation in Finland obtained from pollen analysis and remains from archaeological sites are compared with the changes in population size derived from the summed calendar-year probability distributions. The results from these two independent proxies correlate strongly with one another indicating that population size and the advance of farming were closely linked to each other. Moreover, the results show that the adaptation and development of farming in this area was a complex process comprising several stages and with major differences between regions The most intensive expansion having occurred in and after the Iron Age. It is therefore more accurate to describe the introduction of farming into the area as a long-lasting process, rather than an event.
Agro-pastoral activities in the past act as environmental legacy and have shaped the current cultural landscape in the European Alps. This study reports about prehistoric fire incidents and their impact on the flora and vegetation near the village of Ardez in the Lower Engadine Valley (Switzerland) since the Late Neolithic Period. Pollen, charcoal particles and non-pollen palynomorphs preserved in the Saglias and Cutüra peat bog stratigraphies were quantified and the results compared with the regional archaeological evidence. Anthropogenic deforestation using fire started around 4850 cal. BP at Saglias and aimed at establishing first cultivated crop fields (e.g. cereals) and small pastoral areas as implied by the positive correlation coefficients between charcoal particles and cultural and pastoral pollen indicators, as well as spores of coprophilous fungi. Pressure on the natural environment by humans and livestock continued until 3650 cal. BP and was followed by reforestation processes until 3400 cal. BP because of climatic deterioration. Thereafter, a new, continuous cultivation/pastoral phase was recorded for the Middle to Late Bronze Age (3400–2800 cal. BP). After rather minor human impact during the Iron Age and Roman Period, intensive agriculture was recorded for the Medieval Period. The area around Ardez was used for crop cultivation from about 1000 cal. BP until the start of the ‘Little Ice Age’ (600 cal. BP). Despite a land-use reorganisation, the following gradual decrease in agricultural activities led to the extant mixture of a cultivated, grazed and forested landscape in the Lower Engadine. In addition, this study demonstrates the excellent value of the fungus Gelasinospora as a highly local marker of past and today’s fire incidents, as well as of the use of micro-charcoals from pollen slides and macro-charcoals (>150 µm) from pollen sample residues for the reconstruction of short- and long-term fire histories.
The scarcity of long instrumental series from the Southern Ocean limits our understanding of key climate and environmental feedbacks within the Antarctic system. We present an assessment for the Antarctic mollusc bivalve Yoldia eightsi as an Antarctic coastal climatological archive, based on annually-resolved growth pattern of 20 live-collected specimens in 1988 from Factory Cove, Signy Island (South Orkney Islands). Two detrending methods were applied to the growth increment series: negative exponential detrending and regional curve standardization (RCS) detrending. The RCS-chronology showed consistent synchronous growth in the population for a 20 year period (1968-1988; expressed population signal >= 0.85), a negative correlation between the RCS-chronology and the fast-ice duration record (r= -0.41, N= 24, P<= 0.05) and winter duration (r= -0.52, N=24, P<= 0.01) and positive correlations with mean winter sea surface temperature (SST; r= 0.57, N= 24, P<= 0.01), mean summer SST (r= 0.46, N= 24, P<= 0.05) and mean annual SST (r= 0.48, N= 24, P<= 0.05). The chronology appears to record the environmental conditions generated during the Weddell Polynya event (1973 -1976) as detectable abrupt changes in the annual growth patterns. Over eight years (1973-1980) a negative relationship between shell growth and suspended chlorophyll (i.e. a proxy for surface productivity) is apparent which is likely influenced by the seasonal deposition of organic phytodetritus on the seabed following surface water phytoplankton blooms. Our results form a basis for establishing Y. eightsi as an environmental archive for coastal Antarctic waters.
The Holocene sediment record of Lake Tiefer See exhibits striking alternations between well-varved and non-varved intervals. Here, we present a high-resolution multi-proxy record for the past ~6000 years and discuss possible causes for the observed sediment variability. This approach comprises microfacies, geochemical and microfossil analyses and a multiple dating concept including varve counting, tephrochronology and radiocarbon dating. Four periods of predominantly well-varved sediment were identified at 6000–3950, 3100–2850 and 2100–750 cal. a BP and AD 1924–present. Except of sub-recent varve formation, these periods are considered to reflect reduced lake circulation and consequently, stronger anoxic bottom water conditions. In contrast, intercalated intervals of poor varve preservation or even extensively mixed non-varved sediments indicate strengthened lake circulation. Sub-recent varve formation since AD 1924 is, in addition to natural forcing, influenced by enhanced lake productivity due to modern anthropogenic eutrophication. The general increase in periods of intensified lake circulation in Lake Tiefer See since ~4000 cal. a BP presumably is caused by gradual changes in the northern hemisphere orbital forcing, leading to cooler and windier conditions in Central Europe. Superimposed decadal- to centennial-scale variability of the lake circulation regime is likely the result of additional human-induced changes of the catchment vegetation. The coincidence of major non-varved periods at Lake Tiefer See and intervals of bioturbated sediments in the Baltic Sea implies a broader regional significance of our findings.
In this paper, we reconstruct the Holocene paleoenvironmental evolution of the Guadiana Estuary, southwestern Iberian Peninsula. Two previously studied boreholes (CM3 and CM5) were revisited and analyzed in the light of a foraminifera modern analog approach. Cluster analyses define four assemblages with different biocenotic, taphonomic, elevation and distance-to-sea settings, which serve as a baseline for paleoassemblages interpretation. Faunal changes along the sedimentary sequences, together with previous sedimentological and chronological data, redefine the different phases of environmental evolution in the Guadiana Estuary since ca. 13 kyr cal. BP, with special emphasis on the Holocene marine highstand. Estuarine flooding began synchronously in both locations (ca. 9 kyr cal. BP) but manifested differently in each sedimentary sequence. The most seaward borehole records a more evident and longer highstand (ca. 8.8–3.8 kyr cal. BP), characterized by the occurrence of subtidal environments and by the presence of open marine species (Pararotalia cf. spinigera, planktic forms and a significant number of exotic/allochthonous tests), indicating warmer and more marine conditions than today. In the most landward borehole, the highstand is shorter (ca. 8–7.6 kyr cal. BP) and less intense, characterized by the presence of a diverse, mainly autochthonous, open estuary assemblage, dominated by Ammonia aberdoveyensis and Haynesina germanica. At 4.4 kyr cal. BP, during a long deceleration phase of regional sea-level rise, a short but well-defined pulse of marine influence is recorded in CM5, when open estuarine assemblages reappear and replace marsh agglutinated assemblages, suggesting a new submergence phase. This short event is not identified in the previous works carried out in the same area, thus further data are needed to understand whether it is consequent from a global, warming period or whether it resulted only from local and ephemeral forcing effects.
Quantifying variation in animals’ paleodiet from the fossil record is difficult as a continuous record of their remains is difficult to obtain. Here we assess dietary change in seabirds from Guangjin Island, Xisha Archipelago, South China Sea, by using stable nitrogen isotopes in seabird bones and prey remains collected from a coral sand ornithogenic sediment profile. 15N of seabird bone collagen varied from 11.7 to 14.1 (averaging 12.8 ± 0.4), but that of fish bones and scales showed minor variations. Flying fish and squid are two favorite foods of tropical seabirds, and the average values of muscle 15N in typical flying fish and squid samples were 9.2 and 10.2, respectively. Based on nitrogen isotope mass balance calculation, we conclude that flying fish accounts for 80% ± 40% of seabird diet averaged over the past 1200 years, but this prey accounted for only about 37% ± 30% during the ‘Little Ice Age’ (AD 1400–1850). Flying fish averaged up to 88% ± 2% during the ‘Medieval Warm Period’ (AD 850–1200), close to modern observed value of 89.6%. Thus, it appears that seabirds on Guangjin Island mainly preyed on flying fish during warm periods, and shift to squid during cooler periods. Our results suggest that recent global warming and human activities have likely caused a rapid decrease in tropical seabird population and dietary shift.
Hitherto, the Landscape Reconstruction Algorithm (LRA) has been the only truly quantitative approach to stand-scale palynology. However, the LRA requires information on pollen productivity and dispersal, which is not always available. The alternative approach MARCO POLO (MAnipulating pollen sums to ReCOnstruct POllen of Local Origin) presented here is solely based on pollen values and does not rely on a pollen dispersal function. In a stepwise fashion, MARCO POLO removes those pollen types from the pollen sum whose values are significantly higher than in a neighbouring large basin. The resulting regional pollen sum is free of the disturbing factor of (extra-)local pollen. Based on this sum, comparison with the pollen record from the large basin allows calculating sharp (extra-)local signals. Treating the (extra-)local pollen portion with representation factors (R-values) then produces a quantitative reconstruction of the stand-scale vegetation composition. We tested MARCO POLO and the LRA on a dataset of pollen surface samples and forest vegetation relevés from northern Central Europe. Both approaches reconstruct the presence or absence of taxa at the stand scale within a small margin of error. Where observed cover was >=2%, both models always reconstructed presence, where modelled cover was >=2% the taxon was always present. Overall, both approaches perform well in reconstructing the cover of taxa within a 100-m radius. In our tests, MARCO POLO is slightly better at reconstructing cover values for more taxa. Although some model parameters evidently need revision, the simple correlative approach of MARCO POLO appears to perform at least as well as the complex LRA model.
The Kukkal basin, Tamil Nadu, India, receives most of its rain from the southwest monsoon (SWM). A sediment core from Kukkal Lake preserves a continuous sediment record from the early-Holocene to present (9000 yr BP to present). The present lake is situated at an elevation of ~1887 m a.s.l., in a small basin that appears to have alternated between a and wetland depositional environment. Climate proxies, including sediment texture, total organic carbon (TOC), total nitrogen (TN), C/N, pollen and geochemical composition indicate a steady progression to wetter conditions, with two stepwise changes at about 8000, and between 3200 and 1800 yr BP. The change at 8000 yr BP appears to correspond to a brief (100–150 years) dry spell recorded elsewhere in India. The change at 3200–1800 yr BP consisted in a rapid intensification of the SWM, and may correlate with the initiation of the ‘Roman Warm Period’. There is no clear evidence of changes at the times of the ‘Medieval Warm Period’ (‘MWP’) and the ‘Little Ice Age’ (‘LIA’). The C/N ratio of the sediments ranges from 14.02 to 8.31, indicating that the organic matter originated from a mixture of lacustrine algae, vascular and terrestrial plants. Chemical weathering indices (Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), and Plagioclase Index of Alteration (PIA)) are consistent with extreme silicate weathering. Pollen data show a development from savanna vegetation prior to about 8000 yr BP, followed by grassland with palms, the appearance of ferns just prior to 3200 yr BP and the establishment of the tropical humid forest between 3200 and about 1800 yr BP.
The consequences of climate change and land subsidence are often related to sea level rise/fall. Mangrove extinction and migration were assessed through palynological studies in two sedimentary cores in order to address climate, Relative Sea level (RSL) and its relation to geomorphology since 8420 cal. yr BP from Kanuru (500 cm deep) and since 5850 cal. yr BP from Machilipatnam (118 cm deep), Krishna delta, India. Four units/nine phases of sediment depositional environment were identified on the basis of marine/terrestrial palynomorphs. In Unit 1, the marine palynomorphs indicate palaeoshoreline in Kanuru from 8420 to 8300 cal. yr BP which is now ~4–5 km from the present-day shoreline, but after a short span a retreat in sea level took place between 8300 and 7040 cal. yr BP. About three to four short-term intermittent rise/fall in RSL were recorded in Unit 2 between 7040 and 3980 cal. yr BP in Kanuru and between 5225 and 3240 cal. yr BP in Machilipatnam. During this period, the diversity of mangroves was more in Machilipatnam and only salt-tolerant mangroves were present in Kanuru. Unit 3 is characterized by non-estuarine sediment deposition since 3920–240 cal. yr BP in Kanuru and since 3240–950 cal. yr BP in Machilipatnam. Unit 4 shows a rise in RSL in both the studied sites which began much earlier in Machilipatnam than in Kanuru. Loss of mangrove diversity and dominance of salt-tolerant mangroves were recorded in Unit 4. Results indicate climate-induced RSL fluctuations highlighting the cooling event of 8.2 ka BP from Kanuru site and duration of intermittent rise/fall of RSL during middle Holocene transgression. The rate of sea level rise during the period was not continuous but interrupted by three to four retreats. At present, the evidence of these are at different depths in both the sites and in other contemporary sites along the east coast of India, suggesting neo-tectonics in the vertical stack of Holocene sediment. The geomorphology of the studied sector is tectonically controlled which may increase deltaic instability in future.
The aims of this article are, first, to investigate the middle- and upper-Holocene woodland history along the altitudinal gradient between the lowlands and uplands of Central Europe (190–550 m a.s.l.) and, second, to outline possible biases inherent in the charcoal record based on a comparison with the pollen record and its known biases. Our anthracological data set contains 42,547 determinations made in 120 charcoal samples taken at 69 sites. The lowest elevated part of the study region (below 200 m a.s.l.) is characterized by the long-term presence of a species-rich hardwood forest (mixed oak–elm–ash forest). Quercus charcoals dominated in the rest of the altitude zones during the Neolithic and Aeneolithic; however, shrub charcoals appearing in samples from areas with chernozem soils (generally up to 230 m a.s.l.) indicate open-canopy oak woodlands. The species composition differed along the altitudinal gradient during the Bronze Age period, when Carpinus, Fagus and Abies expanded to altitudes above 230 m a.s.l., while Fagus was more abundant above 290 m a.s.l. Broadleaved trees (Quercus, Fraxinus, Ulmus, Acer and Carpinus) and shrubs are generally more represented in charcoals than pollen. Since broadleaved trees are usually nutrient demanding and able to re-grow easily after being felled, we suppose that their charcoal record is influenced by two main factors: bias of the initial location of the archaeological site and bias caused by long-term human influence on forest vegetation in the vicinity of settlements. These results underline that combining charcoal and pollen analysis has great potential for studying phenomena in cultural landscapes, as each of the methods approaches nature from the opposite side of the human–nature gradient.
Palaeoclimatic reconstruction is a main subject of palaeoecology, clarifying fossil palaeoenvironmental patterns. Our study provides a macroecological approach to reconstruct the mean annual temperature (MAT) of the Pannon region at the early Holocene Thermal Maximum (HTM, warmest period of the Holocene), based on the absence of forest-dwelling conifers in the North Hungarian Mountains and their presence in the surrounding Carpathians on the same altitude. We suppose that the HTM was enough warm to drive conifers to extinction from elevations between 900 and 1100 m a.s.l. in the relatively isolated N-Hungarian Mts. Conversely, HTM still allowed the survival of residual dwarf pine (Pinus mugo) stands on the isolated peaks of the West Transylvanian Mountains between 1600 and 1800 m a.s.l. Our study provides an estimate for the value of MAT of HTM of Pannon region with an interval of 0.4°C, relying on macroecological considerations. We calculate the temperature of the HTM 1.3–1.7°C warmer than the present temperature. This method can be used in a general sense, if conditions meet the requirements of the method even in horizontal cases, with area isolates of climate-sensitive species.
A high-resolution diatom record from Wolf Lake, a minimally disturbed ‘heritage’ lake, provides insights into the hydroclimatic history of the Adirondack Mountains of northern New York during the last c. 1600 years. Three pronounced dry periods occurred during c. AD 490–610, 780–870, and 1010–1080, and low precipitation generally prevailed during the warm Medieval Climate Anomaly (c. AD 950–1350), a finding that fills an important gap in knowledge of the spatial extent of droughts across North America during that period. During the cooler ‘Little Ice Age’ interval (c. AD 1350–1800), inferred water balance was generally more positive. Seven peaks in charcoal abundance represent fire events during both wet and dry periods. Unusually high charcoal and inorganic sediment deposition c. AD 1700 could reflect human activity in the watershed, as might an abrupt rise in the relative abundances of planktonic and tychoplanktonic diatoms in Wolf Lake during the AD 1860s. The diatom record displays periodicities of c. 256 and 512 years in addition to high-frequency fluctuations, suggesting that significant precipitation variability is likely to continue to disrupt climatic trends in this region.
Pollen, non-pollen palynomorphs, charcoal and geochemical analyses of sediments from Lakes Salet and Ruskowiejskie (NE Poland) were used to reconstruct vegetation changes in the former Galindia territory (Old Prussia) related to human activity and the climatic instability of the medieval period. Among archaeologists and historians, there is a widespread opinion that the permanent transformations of the environment in Prussia (south-eastern Baltic region) began not earlier than after its conquest by the Teutonic Order and resulted from its economic activity and intensive colonization. The impact of previous inhabitants of this land on the environment has been considered as definitely weak. Our results provide entirely contrasting evidence and demonstrate that strong and permanent deforestation started as early as in the early 11th century AD, in the pre-Teutonic Order time, and were associated with the economic activity of the Prussian Galinditae tribes. In this paper, we also discuss a possible interpretation of the medieval distribution patterns of Quercus. We assume that human activity catalysed and amplified both its spreading process and decline, primarily driven by the ‘Little Ice Age’ climatic deterioration. Our palynological results indicate the significant spread of Picea from ca. AD 1000, which we interpret as reflecting hydrological and climatic changes. Moreover, we hypothesize that the spread of Carpinus in the early medieval period (11th–13th centuries), which occurred in connection with more intense human activity, was largely because of woodland pasturing.
A lake sediment record from the north-eastern European Russian Arctic was examined using palaeolimnological methods, including subfossil chironomid and diatom analysis. The objective of this study is to disentangle environmental history of the lake and climate variability during the past 2000 years. The sediment profile was divided into two main sections following changes in the lithology, separating the limno-telmatic phase between ~2000 and 1200 cal. yr BP and the lacustrine phase between ~1200 cal. yr BP and the present. Owing to the large proportion of semi-terrestrial chironomids and poor modern analogues, a reliable chironomid-based temperature reconstruction for the limno-telmatic phase was not possible. However, the lacustrine phase showed gradually cooling climate conditions from ~1200 cal. yr BP until ~700 cal. yr BP. The increase in stream chironomids within this sediment section indicates that this period may also have had increased precipitation that caused the adjacent river to overflow, subsequently transporting chironomids to the lacustrine basin. After a short-lived warm phase at ~700 cal. yr BP, the climate again cooled, and a progressive climate warming trend was evident from the most recent sediment samples, where the biological assemblages seem to have experienced an eutrophication-like response to climate warming. The temperature reconstruction showed more similarities with the climate development in the Siberian side of the Urals than with northern Europe. This study provides a characteristic archive of arctic lake ontogeny and a valuable temperature record from a remote climate-sensitive area of northern Russia.
The social impacts of climate change constitute an important field within the study of global change. The impacts of historical climate change on dynastic transitions and prosperity in China from a food safety perspective is a helpful research topic that contributes to a better understanding of the impacts, process, and mechanism of climate change, as well as a reference for projecting the impacts of climate change in the future. This study defined the periods of dynastic transitions and prosperity in China from 210 BC to AD 1910 and analyzed the relationships among dynastic transition or dynastic prosperity, climate change, and grain harvests. From 210 BC to AD 1910, dynastic transitions mostly coincided with cold ages or the periods that changed from warm to cold and dry or wet-to-dry periods when there was relatively poor harvest. In contrast, dynastic prosperity mostly coincided with warm ages or the periods that changed from cold to warm and wet or dry-to-wet periods when there was relatively bumper harvest. Meanwhile, the dynastic transitions from a divisive dynasty to a unified dynasty often came with a progressively warm phase on the century scale when grain harvests increased. Interestingly, the division of a unified dynasty often came with a progressively cold phase and poor harvests. Furthermore, changes in temperature and agricultural production may be one of the most important factors leading to the collapse of Tang Dynasty. In conclusion, the fluctuation of grain harvests and climate change correspond with the transitions between a tumultuous society and an ordered one, which reveals that the social sensitivity periods were often a result of a change to a colder climate on the century scale.
We present a method for analysing subfossil plant cuticles preserved in peat and apply the method to provide a preliminary, coarse resolution reconstruction of Holocene vegetation history at Moanatuatua Bog, northern North Island, New Zealand. The plant cuticle record reveals the early-Holocene development of a swamp and its transition to a raised bog, which is not apparent from other proxies. Comparison with a pollen record from the same sequence highlights the advantages of plant cuticle analysis in cases where pollen is hard to identify or poorly preserved. In particular, distinguishing between the pollen grains of the two main bog species, the restiads Empodisma robustum and Sporadanthus ferrugineus, relies on subtle gradational characteristics, whereas their cuticular patterns are very distinct. Furthermore, Cyperaceae pollen is poorly preserved at Moanatuatua Bog, being almost completely absent, whereas the Cyperaceae cuticles are present throughout the sequence. Therefore, we suggest that Cyperaceae pollen at this site is a less reliable indicator of local sedge communities than the cuticle record. The wide dispersal capabilities of these wind-dispersed pollen types also make them less suitable for determining local site vegetation and environmental change in comparison with cuticle remains. These results suggest that plant cuticle analysis may be a useful tool for the reconstruction of long-term vegetation changes from peat sequences, especially when used in concert with palynology. Sample preparation also proved to be fast with little equipment or chemicals needed.
The Hexi Corridor of northwestern China was a principal axis of cultural interchange between eastern and western Eurasia during the prehistoric and historic epochs. Neolithic groups began dense settlements in Hexi Corridor after 4300 BP with millet crops and polychrome pottery from north China and bronze from Central Asia around 4000 BP accompanied by wheat, barley, and sheep. The impact of these activities on the environment during the late Neolithic and Bronze Age is not clearly understood. Therefore, we analyzed the Cu concentrations of samples collected within cultural layers of anthropogenic sediments from 17 Late Neolithic and Bronze Age sites located within the Hexi Corridor. The Cu content is reported in view of the archaeological and paleoclimatic research undertaken in the area. Our results enabled us to explore the variety of human impact on the environment before and after the introduction of bronze technology into Hexi Corridor. During 4300–4000 BP, Cu concentrations of the anthropogenic sediments were constrained within natural background values. However, from 4000 to 3400 BP, they increased substantially and far exceeded the natural background. The Cu concentrations then declined and remained above the natural background from 3000 to 2400 BP. Our work suggests that the introduction of copper melting technology led to human alteration of sediments’ chemical properties in their surrounding environments in Hexi Corridor since 4000 BP; its intensity was closely related to human settlement density, which was further affected by climate change and livelihood transition in the area during Bronze period.
Although extreme weather events make a strong impact in shallow marine sedimentary environments, there is still a paucity of past records for the Holocene period. Estuarine-inner shelf mud regions deposited from rivers that transport a large amount of suspended sediment represent an important archive of the Holocene. Two cores (S5-2 and JC07) retrieved from the estuarine-inner shelf regions of the East China Sea provided an opportunity to use sensitive grain size and 210Pb dating to reconstruct a history of extreme weather events in the Yangtze River basin. Here, we show that the average sedimentation rates of the two cores, S5-2 (1930–2013) and JC07 (1910–2013), were estimated to be 3.11 and 1.56 cm/yr, respectively. The results indicated that sediment supply played an important role in sedimentation of the estuarine-inner shelf mud region of the East China Sea. Sand content strongly increased in the late 1980s, a result of downstream riverbed erosion of the Yangtze River and submerged deltas. The grain size versus the standard deviation method was used to identify grain-size intervals with the highest variability along a sedimentary sequence. The Yangtze estuary mud area coarse population correlated well with historical literature on Yangtze River floods since AD 1930. Extreme storm events corresponded well with historical literature on the Zhe-Min mud region of the East China Sea. The spectral analyses of the sample core coastal population demonstrated that flood and storm events were consistent with a ~3–8 a periodic change of El Niño Southern Oscillation (ENSO), suggesting that the flood events usually follow ENSO years in the Yangtze River. Consequently, sediment records preserved in the two cores demonstrated different sedimentary responses to Yangtze River floods and storms, which is important to recover centennial scale flood events, to infer extreme precipitation, and to understand climate change in the estuarine-inner shelf of the East China Sea. Nevertheless, more efforts are still needed to simulate paleo-flood and predict future flood events in the context of global warming.
Multiple proxies using variation in 18O, 13C, mineralogy, and petrography in a newly generated high-resolution record of Stalagmite DP1 from Dante Cave indicate a linkage between changes in hydroclimate in northeastern Namibia and changes in solar activity and changes in global temperatures. The record suggests that during solar minima and globally cooler conditions (ca. 1660–1710 and ca. 1790–1830), wetter periods (reflecting longer summer seasons) in northeastern Namibia were linked to advances of the Inter-Tropical Convergence Zone (ITCZ) and the Inter-Ocean Convergence Zone (IOCZ) southwestward. A slight southward push of the Angola–Benguela Front (ABF) during such intervals could also be expected, bringing more rainfall inland. On the other hand, drier and warmer periods in northeastern Namibia, inferred from the increasing 18O trend in Stalagmite DP1 after AD 1715, coincide with globally warmer conditions, and thus a northeastward migration of the ITCZ, specifically with more warming of the Northern Hemisphere (NH). This finding agrees with reducing precipitation observed in the summer rainfall zone of southern Africa since ca. 1900. Therefore, predictions of warming in high-latitude regions of the NH in the next century should suggest that the presently semi-arid climate of northern Namibia may become even drier.
European beech and Norway spruce are late successional tree species that have become rapidly dominant in northern Europe in late-Holocene. The northern distribution limit for natural beech forests is in SE Norway, where beech forests and boreal spruce forests meet. Here we have estimated the size, composition and age of the macroscopic charcoal pool to infer past fire history and the establishment of neighbouring Norwegian beech- and spruce forests. To encompass landscape level scales of variations in the charcoal pool, we have analysed the charcoal record in 100 soil cores that were collected using a restricted random procedure. The sizes of the soil charcoal pools ranged from 2 to 1214 g m–2, and they were significantly more spatially variable in the beech forest landscape than in the spruce forest landscape. We show that today’s beech forests took over the dominance from Norway spruce in the landscape about 300 years ago, and that fire disturbances on the landscape level preceded the establishment of beech in the former spruce forest landscape. Interestingly, large-scale fire disturbances have not occurred ever since beech gained dominance. Conversely, we show that today’s spruce forests took over the dominance from Scots pine in the landscape, and that also the establishment of spruce was preceded by fire disturbances on the landscape level.
Palaeo-earthquake event recorded by loess rapture fissures (N30°–40°W and N40°–50°E trending) and palaeo-mudflow event recorded by red clay deposits were identified at the Machangyuan Ruins in the Huangshui River valley, at the foot of the northeastern Tibetan Plateau. Comparative analysis of grain-size distributions and geochemical elements of local outcrops indicates that the red mudflows were sourced from the gullies on the valley side where unconsolidated Neogene red clay formation was exposed The palaeo-earthquake was associated with regional tectonic structures including a NNW-trending left-lateral strike-slip fault (Lajishan fault) and a NE-trending local fault (Bazhougou fault). Analysis combining optically stimulated luminescence ages and radiocarbon ages of archaeological record dates the palaeo-earthquake and palaeo-mudflow events to ca. 4.80 ka BP. During that stage, many Neolithic settlements distributed around the Machangyuan Ruins. Enhanced human activities of the Majiayao Culture disturbed the landscape of the Minhe Basin causing widespread soil erosion. Contemporaneous storm rain and earthquake mobilized the loosened sediments in the upper stream gullies forming mudflows. The hollow ground around the Machangyuan Ruins was covered by mudflow and the earthquake fissures were filled in by the mudflow at the same time. This study provides important insights into early human impact during climatic and tectonic events in the environmentally vulnerable zones over the world.
This article brings together in a comprehensive way, and for the first time, on- and off-site palaeoenvironmental data from the area of the Central European lake dwellings (a UNESCO World Cultural Heritage Site since 2011). The types of data considered are as follows: high-resolution off-site pollen cores, including micro-charcoal counts, and on-site data, including botanical macro- and micro-remains, hand-collected animal bones, remains of microfauna, and data on woodland management (dendrotypology). The period considered is the late Neolithic (c. 4300–2400 cal. BC). For this period, especially for its earlier phases, discussions of land-use patterns are contradictory. Based on off-site data, slash-and-burn – as known from tropical regions – is thought to be the only possible way to cultivate the land. On-site data however show a completely different picture: all indications point to the permanent cultivation of cereals (Triticum spp., Hordeum vulgare), pea (Pisum sativum), flax (Linum usitatissimum) and opium-poppy (Papaver somniferum). Cycles of landscape use are traceable, including coppicing and moving around the landscape with animal herds. Archaeobiological studies further indicate also that hunting and gathering were an important component and that the landscape was manipulated accordingly. Late Neolithic land-use systems also included the use of fire as a tool for opening up the landscape. Here we argue that bringing together all the types of palaeoenvironmental proxies in an integrative way allows us to draw a more comprehensive and reliable picture of the land-use systems in the late Neolithic than had been reconstructed previously largely on the basis of off-site data.
Thailand has been regarded as a transition zone between the Indian and western North Pacific monsoons which produce most of the precipitation in this area and sustain large-scale agricultural activities. Their different moisture sources and associated transport trajectories could result in distinguishable seasonal variations in rainfall oxygen isotopes (18O). Knowledge about seasonal variability in Thailand monsoon could facilitate agricultural water management and improve our understanding of the Asian monsoon system. In this study, a detailed examination of the intra-seasonal variability of tree-ring cellulose 18O in teak trees from Northwestern Thailand was performed. The results show clear intra-seasonal variability in cellulose 18O, with heavier values in the early rainy season and much lighter values in the later rainy season. Climate correlation analysis indicates that there is a significant and positive correlation between sub-seasonal variation in cellulose 18O and rainfall 18O. A weak and negative correlation with relative humidity (RH) has also been identified. However, there is no relation between intra-seasonal variation in cellulose and that of the amount of rainfall. These results imply that intra-seasonal variability of cellulose 18O in teak trees from Northwestern Thailand may inherit such variability in rainfall 18O and might be slightly shaded by RH. The spatial correlations with large-scale precipitation in the Merged Analysis (CMAP) and Outgoing Longwave Radiation (OLR) data sets indicated seasonal changes in moisture origin and may potentially be used to explore long-term monsoon climate variability on a seasonal scale in subtropical Southeast Asia.
This study explores the history of the development of Sphagnum communities in an ombrotrophic peatland – Bagno Kusowo – over the past 650 years, based on high-resolution plant macrofossil and testate amoebae analysis. Our research provided information related to the length of peatland existence and the characteristics of its natural/pristine state before the most recent human impacts. Changes in the Sphagnum communities before human impact could have resulted from climate cooling during the ‘Little Ice Age’ (LIA). In this cold and unstable hydrological period, among vascular plants, Eriophorum vaginatum and Baeothryon caespitosum dominated in the peatland vegetation. Peat-forming Sphagnum communities survived the drainage conducted during the 20th century at the Bagno Kusowo bog. We provide three important messages through this study: (1) testate amoebae reflect similar hydrological trends in two peat cores despite considerable microhabitat variability, (2) average long-term water level 10 cm below the surface should be a target for active bog conservation and (3) sites like Bagno Kusowo are extremely important to preserve the remains of pristine biodiversity (including genetic diversity of plants and protists) that was completely removed from most of the raised bogs in Europe due to human activities, for example, drainage.
Farming practice in the first period of the southern Scandinavian Neolithic (Early Neolithic I, Funnel Beaker Culture, 3950–3500 cal. BC) is not well understood. Despite the presence of the first farmers and their domesticated plants and animals, little evidence of profound changes to the landscape such as widespread deforestation has emerged from this crucial early period. Bone collagen dietary stable isotope ratios of wild herbivores from southern Scandinavia are here analysed in order to determine the expected range of dietary variation across the landscape. Coupled with previously published isotope data, differences in dietary variation between wild and domestic species indicate strong human influence on the choice and creation of feeding environments for cattle. In context with palynological and zooarchaeological data, we demonstrate that a human-built agricultural environment was present from the outset of farming in the region, and such a pattern is consistent with the process by which expansion agriculture moves into previously unfarmed regions.
Two sediment cores from the Chukchi Sea margin were investigated for the Arctic sea-ice biomarker IP25, along with marine and terrestrial sterols and glycerol dialkyl glycerol tetraethers (GDGTs). This is the first paleoclimatic application of IP25 in the Chukchi-Alaskan region of the Arctic, which is key for understanding Arctic–Pacific interactions and is experiencing rapid sea-ice retreat under present warming. Sea-ice and related circulation conditions were characterized in this study with a multicentury resolution for the long-term Holocene record to multidecadal for the last several centuries. Sea ice was found to be present during the entire record but with considerable spatial and temporal variability. After very low deglacial IP25 values, possibly related to permanent sea ice and/or an iceberg-dominated environment, cores from the upper slope and shelf show IP25 maxima, interpreted as representing a relative proximity to the sea-ice margin, in the early (ca. 8–9 ka) and middle (ca. 5–6 ka) Holocene, respectively. Along with isoprenoid GDGT distribution, this asynchronicity in sea-ice history probably reflects oceanographic evolution of the Chukchi margin affected by the Beaufort Gyre circulation and Pacific water inflow via Bering Strait. Data for the last several centuries, with elevated values of brassicasterol and terrestrial sterols covarying with dinosterol and IP25, are interpreted in terms of long-distance import by currents combined with diagenetic transformations. We infer that high-amplitude variability in the late ‘Little Ice Age’, starting in the late 18th century, is related to the intensity of the Alaskan Coastal Current. This interval is preceded by three centuries of presumably diminished Alaskan Coastal Current but overall increased Bering Strait Inflow resulting in reduced sea-ice cover according to dinocyst-based data.
Aeolian–coastal sediments and landforms are excellent palaeoenvironmental archives, but chronological studies of coastal records are scarce in Sweden. In this study, we provide luminescence and radiocarbon ages of aeolian activity and coastal landscape evolution on the Kristianstad plain, SE Sweden, based on the investigations of two foredunes and two inland dunes at Åhus and Vittskövle. Additionally, we do a laboratory intercomparison of five young luminescence samples. The comparison shows a significant age difference most likely due to an instrumental difference. The equivalent dose cannot be determined accurately with the low irradiation times, and therefore, the results obtained from the reader with a lower dose rate are favoured and are largely supported by historical records. The oldest age, 11.6 ka, is from littoral sediments underlying an aeolian dune at Vittskövle and represents deposition in the Baltic Ice Lake. These deposits are topped by an organic horizon, which developed between AD 1476 and 1637, a time that partially corresponds with a short and abrupt climate warming in the ‘Little Ice Age’. The aeolian deposits are all younger. Sand mobilisation in the inland dunes took place around AD 1686–1799, related to forest destruction during war, intense cultivation of land or/and the coldest phase of the ‘Little Ice Age’. The foredunes are younger and were deposited at the beginning and in the end of the 20th century by easterly winds.
Tree rings are commonly used proxy data for past climate variability. Probably the simplest practical solution for transforming raw tree-ring data into proxy estimates and retaining information on low-frequency tree-growth forcing is the regional curve standardization (RCS). This paper reviews the RCS concept and the development of this standardization method over the past 25 years. Tree-ring based estimation of low-frequency climate variability is illuminated with a growing diversification of the original concept. The RCS-type methods are seen to remain as essential tools in palaeoclimate research while the RCS chronologies of tree-ring and other incremental proxy data remain the only source for calendar year dated short-to-long timescale climate variations.
The Holocene–Pleistocene transition in the upland loess-mantled regions of the central Great Plains is punctuated by the Brady Soil, which separates the late-Pleistocene Peoria Loess and the Holocene Bignell Loess. Previous research on the Brady Soil at the Old Wauneta Roadcut site in Southwestern Nebraska has produced paleoenvironmental information based on well-constrained luminescence and radiocarbon ages, stable carbon isotope data, and chemical and physical data. While the research indicated high effective moisture during formation of the Brady Soil and a shift to warm-season C4 vegetation from the cool-season C3-dominated vegetation of the Peoria Loess, those data do not provide any detail as to plant community composition and significant underlying climatic inferences. Assemblages of phytoliths and other biosilicates extracted from the Brady Soil provide specific information on vegetation communities and indicate shifts of plant taxa comprising these assemblages. Short-cell phytolith count data reveal a shift from dominance of Pooideae (C3) grasses, with relatively large numbers of arboreal dicot spheres and a few Cyperaceae (sedge) present in a savannah or open woodland in the Bølling-Allerød, to a mixed, open Chloridoideae (C4) and Pooideae (C3) grassland in the early-Holocene. Stipa-type Pooideae, a cool-season grass preferring drier soil conditions, marks the onset of the Younger Dryas. Large-cell phytoliths such as long cells, bulliforms, and trichomes, provided further definition of the climate history. This comprehensive biosilicate study of the Brady Soil has provided a more detailed paleoclimatic reconstruction than that generated with bulk sediment-derived 13C data, or even with short-cell phytolith data alone.
A lake sediment profile spanning the last ~3200 years from Laguna Zoncho in the southern Pacific region of Costa Rica was analyzed for sub-fossil chironomids. Notable shifts in chironomid assemblages occurred during the late-Holocene. A distinct chironomid community, dominated by Tanypodinae such as Procladius and Labrundinia, appeared after ~550 cal. yr BP (~1400 CE). Prior to this time, the chironomid assemblage was more diverse, with taxa such as Paratanytarsus, Tanytarsus type N, and Cladotanytarsus important constituents of the chironomid community. A chironomid-based inference model for mean annual air temperature (MAAT), developed using partial least squares (PLS 2-component), was applied to sub-fossil chironomid assemblages from Laguna Zoncho to reconstruct late-Holocene thermal variability for the region. The key findings from this study are as follows: (1) chironomid-inferred MAAT at ~2740–1220 cal. yr BP (790 BCE–730 CE) was 1.2°C higher than the late-Holocene (~3200 cal. yr BP to present in this study) average of 21.3°C; (2) MAAT at ~470–90 cal. yr BP (1480–1860 CE) was 1.3°C lower than the late-Holocene average, potentially reflecting ‘Little Ice Age’ (LIA) cooling; and (3) evidence for an extended period of low lake levels between 1220 and 840 cal. yr BP (730–1110 CE) possibly indicated the influence of the Terminal Classic Drought (TCD) in southern Costa Rica. This study pioneers the use of sub-fossil chironomid remains to develop quantitative estimates of Holocene thermal variability and environmental change in Central America.
To evaluate whether proxies that record surface, near-surface, and bottom water conditions from the North Iceland shelf have similar trends and periodicities, we examine Holocene century-scale paleoceanographic records from core MD99-2269. This core site lies close to the boundary between Atlantic and Arctic/Polar waters, and in an area frequently influenced by drift ice. The proxies are stable 13C and 18O values on planktonic and benthic foraminifera, alkenone-based sea-surface temperatures (SST°C), and foraminiferal Mg/Ca SST°C and bottom water temperature (BWT°C) estimates. These data were converted to equi-spaced 60-year time-series; significant trends were extracted using Singular Spectrum Analysis, which accounted for between 50% and 70% of the variance. In order to evaluate within-site ocean climate variability, a comparison between these data and previously published proxies from MD99-2269 was carried out on a standardized data set of 14 proxies covering the interval 400–9200 cal. yr BP. Principal component (PC) analysis indicated that the first two PC axes accounted for 57% of the variability with high loadings primarily defining ‘nutrient’ and ‘temperature’ proxies. Fuzzy k-mean clustering of the 14 climate proxies indicated major environmental changes at ~6350 and ~3450 cal. yr BP, which define local early-, middle-, and late-Holocene climatic shifts. Our results indicate that the major control on the combined proxy signal is the Holocene decrease in June insolation, but regional changes in such factors as sea-ice extent and salinity are required to explain the threefold division of the Holocene.
Reconstruction of Skagerrak deep-water renewal is used to assess regional changes in winter thermal conditions over the past 6800 years. Changes in winter climate conditions from the Skagerrak region are in turn linked to shifts in Holocene large-scale atmospheric circulation patterns prevailing over northern Europe. We use Melonis barleeanus Mg/Ca from two sediment cores in the central Skagerrak to reconstruct temperature of Skagerrak intermediate water, representing the warm season temperature variability, and deep water, for monitoring Skagerrak deep-water renewal, reflecting the winter temperature variability. In addition, M. barleeanus 18O is used from the deeper core to reconstruct salinity, also monitoring the deep-water renewal. Our results show that the Skagerrak deep-water experienced phases of particularly enhanced renewal during the mid-Holocene reflecting severe winter conditions, followed by a general shift to reduced renewal as a consequence of milder winter conditions over the North Sea around 3500 cal. yr BP. The late-Holocene shift was most likely related to the onset of a regime with intensified winter westerly winds directed toward northern Europe and an increased inflow of North Atlantic water into the Skagerrak–North Sea reflecting more maritime climate conditions. On millennial scale, cold phases in our deep-water records match with low winter precipitation phases in western Norway. They are associated with distinct increases in ice rafted debris (IRD) in North Atlantic sediments, suggesting that phases of iceberg discharge in the Atlantic were associated with cold and dry winter conditions over northern Europe. Interestingly, the cold event centered around 5900 cal. yr BP appears to be only associated with winter variability, while the following one at 4200 cal. yr BP is documented in our winter record, as well as in records related to warmer seasons.
Over the recent decades, glaciers have in general continued to lose mass, causing surface lowering, volume reduction and frontal retreat, thus contributing to global sea-level rise. When making assessments of present and future sea-level change and management of water resources in glaciated catchments, precise estimates of glacier volume are important. The glacier volume cannot be measured on every single glacier. Therefore, the global glacier volume must be estimated from models or scaling approaches. Volume–area scaling is mostly applied for estimating volumes of glaciers and ice caps on a regional and global scale by using a statistical–theoretical relationship between glacier volume (V) and area (A) (V = cA) (for explanation of the parameters c and , see Eq. 1). In this paper, a two-dimensional (2D) glacier model has been applied on four Norwegian ice caps (Hardangerjøkulen, Nordre Folgefonna, Spørteggbreen and Vestre Svartisen) in order to obtain values for the volume–area relationship on ice caps. The curve obtained for valley glaciers gives the best fit to the smallest plateau glaciers when c = 0.027 km3–2 and = 1.375, and a slightly poorer fit when the glacier increases in size. For ice caps, c = 0.056 km3–2 and = 1.25 fit reasonably well for the largest, but yield less fit to the smaller.
This study aims to quantify the contribution of Yangtze clays to the sediment accumulation in the western Taiwan Strait and reconstruct the strength of Chinese Coastal Current (CCC) since middle-Holocene driven by East Asian Winter Monsoon (EAWM). Both down-core and surficial sediment samples were collected for grain size, radiocarbon, and clay mineral analyses. One 250-cm-long core was collected from the southern Yangtze distal mud wedge in western Taiwan Strait which receives Yangtze-derived clays transported by the Zhejiang-Fujian Coastal Current (ZFCC), the southern part of CCC. Clay minerals were examined in surficial sediment samples which were influenced by the Yangtze, Zhejiang-Fujian, western Taiwanese rivers, and the inner-shelf mud wedge. Ternary diagrams of smectite–kaolinite–chlorite revealed that three endmembers represented the Yangtze, Min, and western Taiwanese rivers, respectively. The estuaries seaward of the tidal current limits of Zhejiang-Fujian rivers, especially the Qiantang and Ou, were influenced by Yangtze-derived sediments through energetic tidal mixing. It was found that smectite can be used as a fingerprint of the Yangtze fine-grained sediment because among all the studied rivers, the Yangtze is the only one supplying smectite. Clay mineral results in core sediments revealed a dramatic provenance change at the depth of 113 cm, dated at ~4.0 cal. kyr BP. Smectite disappeared in the upper core, suggesting decreased contribution of Yangtze clays to the southern distal mud wedge. Decreased grain size of the fine population in the upper core also indicated that the ZFCC weakened during the late-Holocene. Such a decline also occurred in Subei Coast Current (northern part of CCC), revealed by the previous studies. The decline of CCC was related to the decreased EAWM of the late-Holocene, and it resulted in decreased sediment accumulation rate of the inner-shelf mud.
For well over a century, scholars from across the social and biological sciences have been trying to understand the origins and spread of agriculture. This debate is often intertwined with discussions of climate change and human environmental impact. Over the past decade, this debate has spread into Central Eurasia, from western China to Ukraine and southern Russia to Turkmenistan, a part of the world often thought to have been largely dominated by pastoralists. A growing interest in the prehistory of Central Eurasia has spurred a new chapter in the origins of agriculture debate; archaeobotanical research is showing how important farming practices in this region were in regard to the spread of crops across the Old World. While early people living in Central Eurasia played an influential role in shaping human history, there is still limited understanding of the trajectories of social evolution among these populations. In March 2015, 30 leading scholars from around the globe came together in Berlin, Germany, to discuss the introduction and intensification of agriculture in Central Eurasia and adjacent regions. At the German Archaeological Institute in Berlin (Deutsches Archäologisches Institut, DAI), these scholars presented novel data on topics covering East, South, and Central Asia, spanning a wide realm of methodological approaches. The present special edition volume deals with a selection of the papers given at this conference, and it marks a significant step toward recognizing the contribution of Central Eurasian populations in the spread and development of agricultural systems over the course of the Holocene.
The Holocene history of outlet glaciers affords information on the behavior and mechanisms controlling the extent of the East Antarctic Ice Sheet. Here, we present both new radiocarbon and recalculations of previously published cosmogenic exposure-age data that constrain Holocene ice dynamics along upper Reedy Glacier in the southernmost Transantarctic Mountains. Ice remained at or close to its last glacial maximum position until the early Holocene, at which time it underwent thinning. A period of apparent relative stability in the mid-Holocene led to the formation of ice-dammed proglacial ponds, as well as of moraines located roughly two-thirds of the distance from the maximum position to the present-day ice margin. Renewed thinning began after 3600 yr BP, with ice reaching present-day levels by 2400 yr BP. Ice variations along upper Reedy Glacier likely reflect the balance between upstream propagation of mechanical thinning events at the glacier mouth and regional accumulation changes.
Palaeoecological and archaeological studies have demonstrated that human populations have long inhabited the moist forests of central Africa. However, spatial and temporal patterns of human activities have hardly been investigated with satisfactory accuracy. In this study, we propose to characterize past human activities at local scale by using a systematic quantitative and qualitative methodology based on soil charcoal and charred botanical remains. A total of 88 equidistant test-pits were excavated along six transects in two contrasting forest types in southern Cameroon. Charred botanical remains were collected by water-sieving and sorted by type (wood charcoals, oil palm endocarps and unidentified seeds). A total of 50 Accelerator Mass Spectrometry 14C dates were also obtained. Results showed that charred macroremains were found at multiple places in the forest, suggesting scattered human activities, which were distributed into two main periods (Phase A: 2300–1300 BP; Phase B: 580 BP to the present). Charred botanical remains indicated two types of land-use: (1) domestic, with oil palm endocarps most often associated with potsherds (villages) and (2) agricultural, with charcoal as probable remnant of slash-and-burn cultivation (fields). Oil palm endocarp abundance decreased with distance from the identified human settlements. Our methodology allowed documenting, at high resolution, the spatial and temporal patterns of human activities in central African moist forests and could be applied to other tropical contexts.
This study is focused on a 3.55-m-long sediment core retrieved from Badanital (i.e. the BT core) in 2008. Badanital (30°29'50''N, 78°55'26''E, 2083 m a.s.l.) is a small lake located in the upper catchment area of the Ganges in Garhwal Himalaya, northern India. The lake and the regional broad-leaved semi-evergreen forests are under the influence of the Indian Summer Monsoon (ISM) and westerly associated cyclones. Palynological investigation of the BT core revealed past vegetation changes reflecting both climate and human impact during the last 4600 years. Maximum spread of oaks occurred during c. AD 550–1100 and c. AD 1400–1630, that is, the intervals which partly overlap with the ‘Medieval Warm Period’ and the ‘Little Ice Age’, respectively. Three intervals of decreased oak pollen percentages are attributed to (1) continuously drier and cooler climatic conditions and fire activity (c. 2600–500 BC), (2) severe reduction in oak forests followed by secondary succession of alder woods (c. AD 1150–1270) and (3) pre-modern settlement activities since the British imperial occupation (after c. AD 1700). We argue that the high percentages (i.e. up to 28%) of Humulus/Cannabis type and Cannabis type pollen point to intense local retting of hemp c. 500 BC–AD 1050. Based on our age model, Cannabis fibre production at Badanital is contemporaneous with archaeological records of ancient hemp products from different parts of Eurasia suggesting possible linkages to early trade and knowledge exchange routes connecting India and the Himalaya with Central and East Asia and possibly Europe.
A 2665-year ring-width chronology was developed based on Qilian juniper from the upper treeline of the Animaqin Mountains on the eastern Tibetan Plateau. Correlation analysis results showed that the chronology was significantly negatively correlated with April–June maximum temperature at nearby meteorological stations, indicating that maximum temperature is the factor that limits tree growth in this area. Accordingly, we reconstructed the average April–June maximum temperature variations since 261 BC. Our regression model explained 37.9% of the total variance for the whole calibration period of 1960–2012. Our reconstruction revealed that the maximum temperature started to increase from approximately 1750 without a rapid warming trend, and the warmest period was from AD 890 to 947, as opposed to the recent period, whereas the period from AD 351–483 was the coldest. Significant periods in the wavelet power spectrum were approximately 2–8 years, 20–30 years, 30–60 years, and 60–130 years, as well as some long-term periods (more than 200 years). Comparisons with other temperature series from neighboring regions and the Northern Hemisphere as a whole support the validity of our reconstruction and suggest that it provides a representation of the temperature change for the Animaqin area, although asymmetric variation patterns in minimum and maximum temperatures were found.
Palaeoethnobotanical research at the Yuezhuang site, a Houli Culture settlement in Jinan, Shandong Province, China, dating to 8000–7700 cal. BP, documents human–environment interaction and the local subsistence economy soon after the initiation of food production in the region. This economy supported a sizeable community that occupied a kilometer stretch of floodplain along the Nandasha River. The research explores plant domestication, the extent to which the Yuezhuang population had developed a food production niche, and, to a lesser extent, the development of agriculture in the lower Yellow River valley. In order to do so, charred seeds from a variety of plant taxa were recovered by flotation of sediment from pits and cultural strata. Just over 30% of the seed assemblage is rice (Oryza sativa), broomcorn/common millet (Panicum miliaceum), and foxtail millet (Setaria italica subsp. italica). The status of several other plants such as soybean (Glycine max subsp. max or G. max subsp. soja), perilla (Perilla sp.), and chenopod (Chenopodium sp.) that are also cultivated in East Asia is also assessed. Most of the plant taxa are from open, sunlit, and anthropogenic, disrupted habitats. Diverse grasses similar to those found at later sites indicate that the farming niche documented at the late Neolithic Longshan Culture in Shandong Province was being established by 8000–7700 cal. BP. The plant remains assemblage is compared with three assemblages, two belonging to the Houli Culture and one from the late Neolithic Longshan Culture. Anthropogenic habitats and their formation, maintenance and use, wetland exploitation, cultivation, hunting–gathering–fishing, and animal management characterize the mature (late) Houli Culture niche.
This study investigated the influence of sea-level and climate changes on the decreased fluvial aggradation and subsequent widespread peat initiation in the middle to late-Holocene in the Ishikari lowland, which is a coastal floodplain formed in response to the postglacial sea-level change. By introducing a new approach to separately evaluate the rates of organic and clastic sediment input, we demonstrated that the peat began to form when the fluvial sedimentation rate was significantly decreased (less than 0.6 mm/yr), while plant macrofossil analysis suggested that lowering of water level is also important to the peat initiation. Such changes in sedimentary environment may be associated with the abrupt abandonment of crevasse splays. The concentrated ages of the peat initiation around 5600–5000, 4600–4300, and 4100–3600 cal. BP suggest that an allogenic control promoted the abandonment of crevasse splays, and different onset ages can be explained by different fluvial responses of the Ishikari River and its tributaries. The abandonment of crevasse splays could result from sea-level fall or decreased precipitation. While submillennial sea-level fluctuations coincident with the peat initiation have not been reported in coastal lowlands of Japan, the close comparison of the onset ages and decreased precipitation recorded in a stalagmite from China, which represents the strength of the East Asian summer monsoon (EASM), suggests that decrease in precipitation led to the abandonment of crevasse splays. Our results may indicate that similar fluvial responses might be common in other coastal floodplains affected by the EASM.
The stratigraphy within coastal river valleys in south-central Chile clarifies and extends the region’s history of large, earthquakes and accompanying tsunamis. Our site at Quidico (38.1°S, 73.3°W) is located in an overlap zone between ruptures of magnitude 8–9 earthquakes in 1960 and 2010, and, therefore, records tsunamis originating from subduction-zone ruptures north and south of the city of Concepción. Hand-dug pits and cores in a 3-m-thick sequence of freshwater peat in an abandoned meander (a little-examined depositional environment for tsunami deposits) and exposures along the Quidico River show five sand beds that extend as much as 1.2 km inland. Evidence for deposition of the beds by tsunamis includes tabular sand beds that are laterally extensive (>100 m), well sorted, fine upward, have sharp lower contacts, and contain diatom assemblages dominated by brackish and marine taxa. Using eyewitness accounts of tsunami inundation, 137Cs analyses, and 14C dating, we matched the upper four sand beds with historical tsunamis in 2010, 1960, 1835, and 1751. The oldest prehistoric bed dates to 1445–1490 CE and correlates with lacustrine and coastal records of similar-aged earthquakes and tsunamis in south-central Chile.
The period from the late third millennium BC to the start of the first millennium AD witnesses the first steps towards food globalization in which a significant number of important crops and animals, independently domesticated within China, India, Africa and West Asia, traversed Central Asia greatly increasing Eurasian agricultural diversity. This paper utilizes an archaeobotanical database (AsCAD), to explore evidence for these crop translocations along southern and northern routes of interaction between east and west. To begin, crop translocations from the Near East across India and Central Asia are examined for wheat (Triticum aestivum) and barley (Hordeum vulgare) from the eighth to the second millennia BC when they reach China. The case of pulses and flax (Linum usitatissimum) that only complete this journey in Han times (206 BC–AD 220), often never fully adopted, is also addressed. The discussion then turns to the Chinese millets, Panicum miliaceum and Setaria italica, peaches (Amygdalus persica) and apricots (Armeniaca vulgaris), tracing their movement from the fifth millennium to the second millennium BC when the Panicum miliaceum reaches Europe and Setaria italica Northern India, with peaches and apricots present in Kashmir and Swat. Finally, the translocation of japonica rice from China to India that gave rise to indica rice is considered, possibly dating to the second millennium BC. The routes these crops travelled include those to the north via the Inner Asia Mountain Corridor, across Middle Asia, where there is good evidence for wheat, barley and the Chinese millets. The case for japonica rice, apricots and peaches is less clear, and the northern route is contrasted with that through northeast India, Tibet and west China. Not all these journeys were synchronous, and this paper highlights the selective long-distance transport of crops as an alternative to demic-diffusion of farmers with a defined crop package.
The Gorgan Plain (NE Iran) is characterized by fertile soils formed on a loess plateau and is at present primarily exploited for intensive agriculture. However, the timing and intensity of the human impact on the landscape in the past are still unclear. A sediment core, taken from the centre of the eastern Gorgan Plain in the Kongor Lake covering the major part of the Holocene from 6.1 to 0.8 ka (all ages are calibrated before present), has been studied for pollen, non-pollen palynomorphs, botanical macroremains, insects, charcoal, geochemistry, biomarkers and magnetism in order to provide new insights into the evolution of the landscape and to estimate the intensity of human activities. The data obtained suggest a dry period between 5.9 and 3.9 ka and an increase in regional humidity afterwards with a maximum between 2.7 and 0.7 ka, during the period of the Persian empires (Achaemenid through Sasanian) and the Islamic era. The eastern part of the Gorgan Plain was characterized by open steppe landscapes during the last 6 ka, which most likely were used for pasture and at least since 2.7 ka for agriculture including arboriculture. The strongest anthropogenic impact on the environment around the Kongor site is documented during the Parthian and Sasanian Empires (200 BC–651 AD) and the Islamic era up to the eve of the Mongol invasion.
Lack of documentation on past harvest fluctuations limits the exploration of long-term trends in crop production and agricultural adaptation strategies. A long-term perspective is needed, however, to understand the wide spectrum of potential human responses to environment and climate change. Therefore, we used tree-ring density series as proxy data to reconstruct climate-mediated yield ratio (harvested grain in relation to sown) in central and northern Finland over the period
Arctic lakes and wetlands contribute a substantial amount of methane to the contemporary atmosphere, yet profound knowledge gaps remain regarding the intensity and climatic control of past methane emissions from this source. In this study, we reconstruct methane turnover and environmental conditions, including estimates of mean annual and summer temperature, from a thermokarst lake (Lake Qalluuraq) on the Arctic Coastal Plain of northern Alaska for the Holocene by using source-specific lipid biomarkers preserved in a radiocarbon-dated sediment core. Our results document a more prominent role for methane in the carbon cycle when the lake basin was an emergent fen habitat between ~12,300 and ~10,000 cal yr BP, a time period closely coinciding with the Holocene Thermal Maximum (HTM) in North Alaska. Enhanced methane turnover was stimulated by relatively warm temperatures, increased moisture, nutrient supply, and primary productivity. After ~10,000 cal yr BP, a thermokarst lake with abundant submerged mosses evolved, and through the mid-Holocene temperatures were approximately 3°C cooler. Under these conditions, organic matter decomposition was attenuated, which facilitated the accumulation of submerged mosses within a shallower Lake Qalluuraq. Reduced methane assimilation into biomass during the mid-Holocene suggests that thermokarst lakes are carbon sinks during cold periods. In the late-Holocene from ~2700 cal yr BP to the most recent time, however, temperatures and carbon deposition rose and methane oxidation intensified, indicating that more rapid organic matter decomposition and enhanced methane production could amplify climate feedback via potential methane emissions in the future.
Stabilized sand sheets and dunes hold a remarkable amount of information on paleoenvironmental conditions under which late Quaternary landscapes evolved in northern subarctic regions. We provide the results of a project focused on understanding the development of lowland environments and ecosystems, including dunes and sand sheets, which were critical habitat for early human occupations in subarctic regions. Our study area is the Rosa-Keystone Dunes Field in the Shaw Creek Flats of the middle Tanana River basin, interior Alaska, one of the oldest continuously occupied areas in North America (14,000 cal. BP to present). The disturbance regimes of reactivated dunes and associated forest fire cycles between 12,500 and 8800 cal. BP fostered a unique early to mid-successional mixed vegetation community including herbaceous tundra, shrubs, and deciduous trees. This environment provided key habitats for large grazers and browsers, significant resources for early hunter-gatherer populations in central Alaska. After 8000 cal. BP, the expansion of black spruce and peatlands heightened landscape stability but decreased the range of local habitat for large grazers. Hunter-gatherer economic change during these periods is consistent with human responses to local and regional landscape disturbance and restructuring.
Dust deposition in two ombrotrophic peatlands (Baie and Ile du Havre peatland (IDH) bogs) of the Estuary and Gulf of the St. Lawrence in eastern Canada was reconstructed using elemental geochemistry. The rare earth elements (REEs) and other lithogenic element concentrations were measured by ICP-oES and Q-ICP-MS along two peat cores spanning the last 4000 years. Principal component analyses on the geochemical profiles show that REEs display the same behavior as Al, Ti, Sc, and Zr, all conservative elements, which suggests that REEs are immobile in the studied peat bogs and can be used as tracers of dust deposition. Plant macrofossils were also used to infer past environmental and humidity changes. The dust fluxes were reconstructed using the sum of REEs (REE). The range of dust deposition varies from 0.2 to 3.8 g m–2 yr–1 in the Baie bog, while the IDH bog shows lower fluxes ranging between 0.1 and 1.2 g m–2 yr–1. The highest dust fluxes in the Baie bog were recorded from 1750–1000 cal. BP to 600–100 cal. BP and occur at the same time as periods of high variability in the macrofossil record (i.e. successive layers dominated by Sphagnum or Ericaceae). The timing of these events in the dust and macrofossil records also corresponds to documented cold periods. These two periods have been identified as episodes of climatic instability, which could have been caused by changes in the wind regime.
Integration of geomorphological, stratigraphic, malacological, sedimentological and micropalaeontological techniques and 14C dating allows us to characterise the processes and evolution of the coastal barrier–lagoon system of Valencia (Spain), from the middle Holocene to the historical epoch, as well as the responses to global climate events. Four stages are recognised. Phase 1: around 8240 ± 80 cal. yr BP, a brackish lagoon of moderate energy and in restricted environment was formed, with an energy peak that could correspond to the maximum Holocene marine transgression. Dating (8240 ± 80 cal. yr BP) carried out in peat corresponds to a cold cycle and low water levels in inland lakes of the western Mediterranean. Phase 2: from 6450 cal. yr BP to 3710 ± 130 cal. yr BP, a lagoon remained, in restricted environment and connected with the sea, but with a notable energy decrease and recurrent saturation processes similar to those described in other Mediterranean continental lakes. This phase is contemporaneous with a period of increase in the aridity trend and global cold cycles. Phase 3: from 3710 ± 130 cal. yr BP, a brackish lagoon without marine connection was formed. Towards 820 ± 90 cal. yr BP, a shift to a totally isolated lagoon environment took place (changing from brackish lagoon to freshwater). This process is coeval with a palaeohydrological phase of high flooding frequency in the river flood plains of Spain and Southern France. Phase 4: freshwater lagoon environment becomes a widespread flood plain. During a phase of high frequency and magnitude of floods (‘Little Ice Age’), the flood plain is formed on the top level of the sequence. Phases and processes recorded in sedimentation could be placed in relation with global mid-to-late Holocene events.
Agricultural land use has been established as the dominant prehistoric human activity in early cultural centers for thousands of years. However, because of lack of data, there is still considerable debate about the amount and spatial distribution of prehistoric land use across the world. Quantitative reconstruction of it on the basis of human activity records, for example, archaeological data, is the key to resolving the issue. Here, we focus on one of the most representative regions for prehistoric human activity in northern China, the Wei River valley. Based on archaeological and environmental data, a recently developed quantitative prehistoric land use model (PLUM) is applied to reconstruct spatial and temporal changes of land use between 8 and 4 ka BP. The results reveal that in line with increases in the total number of archaeological sites (from 24 to 3222) and population (from 4000 to 1,550,000), the land area of the valley used by humans increased from 0.2% to 12% during the study interval, expanding from the gentle slopes along the lower reaches of the river to the middle and upper reaches. Meanwhile, the average population for an individual site increased from 160 to 481, but the average land use area per site decreased from 12.84 to 4.68 km2. Since 6 ka BP, the significant land use increase occurred synchronously in the Wei River valley and other key regions of agricultural origin across the world, which highlights the important role of agriculture activity in transforming the nature of global land cover during the prehistoric period.
Dietary changes in the populations inhabiting southwest Siberia and northern Kazakhstan indicate concurrent changes in the economy, at the same time marking the beginnings of East–West interaction across northern Eurasia. The introduction of domestic animal species of Near Eastern origin, such as sheep and goat, dramatically changed the lives of the local population. Past palaeodietary research using stable isotope analysis has mainly focussed on pastoral populations of the Bronze Age period. It is crucial, however, to assess the diets of humans and animals from earlier periods (Neolithic/Chalcolithic) in order to understand the timing and nature of dietary change during the Bronze Age of southwest Siberia and northern Kazakhstan, in particular the possible contribution of environmental change influencing dietary shifts. In this paper, we report the results of stable isotope analysis on 55 human and 45 faunal samples from southwest Siberia (Upper Ob River) and northern Kazakhstan (Tobol River basin), ranging from the Neolithic to the Bronze Age. These data, combined with published human and faunal collagen results from the region as well as new accelerator mass spectrometer (AMS) radiocarbon dating results, indicate little change in animal diet over time, but a notable change in human diet at ca. 2500 cal. BC. The data allow us to determine the time when pastoralism came to the fore, with concomitant economic differences to the local population.
We present simulations for the late-Holocene glacier advances in the Hailuogou catchment, Gongga Shan, in attempts to test the glacier sensitivity to climate changes and constrain the climate conditions that support these glacier advances. We use a coupled mass-balance and ice-flow model parameterized using empirical glaciological and climatological data to simulate the glacier extents by fitting modeled glaciers to corresponding glacial landforms. The glacier sensitivity test showed that in the Hailuogou catchment, glacier area expands increasingly quickly until 4°C cooling, beyond which decreased expansion occurs up to at least 5°C cooling, but the modeled glacier volume increases steadily up to 5°C with an approximate linear rate being 1.1 x 109 m3/0.5°C. The temperatures were estimated to be 1.9–3.1°C, 1.5–2.6°C, and 1.0–2.2°C cooler than present for the respective Guanjingtai, Hailuogou, and ‘Little Ice Age’ (‘LIA’) Maximum glacial stages, considering a realistic precipitation field being 80–120% of present value. Model results also suggested that the Hailuogou catchment was covered by glaciers of 64.1, 59.3, and 53.8 km2 and ice volumes of 8.79 x 109, 7.99 x 109, and 6.92 x 109 m3 in the Guanjingtai, Hailuogou, and ‘LIA’ Maximum glacial stages, respectively. These findings help to understand the relationships between glacier dynamic and climate change and the hydrological evolution in the Hailuogou catchment. We therefore encourage using the model as a powerful tool to retrieve past ice extents and evaluate their related climate conditions on the vast Tibetan Plateau.
The animal species depicted in the rock art of Shuwaymis, Saudi Arabia, provide a record of Holocene climatic changes, as seen by the engravers. Of 1903 animal engravings, 1514 contained sufficient detail to allow identification with confidence. In addition, the stratigraphy of the engravings and the depiction of domesticates provide a broad chronological framework that allows a division into images created during the Holocene humid phase and animals represented after the onset of desert conditions. Despite the large sample size, only 16 animal species could be identified, which represents an extraordinarily narrow species spectrum. Comparison with the scarce faunal record of the Arabian Peninsula shows that all larger animals that are thought to have been present in the area were also depicted in the rock art. The contemporaneous presence of at least four large carnivores during the Holocene humid phase suggests that prey animals were abundant, and that the landscape consisted of a mosaic of habitats, potentially with thicker vegetation along the water courses of the wadis and more open vegetation in the landscape around them. Community Earth System Models (COSMOS) climate simulations show that Shuwaymis was at the northern edge of the African Summer Monsoon rainfall regime. It is therefore possible that Shuwaymis was ecologically connected with southwestern Arabia, and that an arid barrier remained in place to the north, restricting the dispersal of Levantine species into Arabia.
The Baffin Island region in the eastern Canadian Arctic has recently experienced a rapid warming, possibly unprecedented in millennia. To investigate the response of freshwater environments to this warming and place it in a secular perspective, we analyzed a 90-cm-long sediment core from Nettilling Lake, the largest lake of the Canadian Arctic Archipelago. The core was taken from a part of the lake basin that receives meltwater and sediment inputs from the nearby Penny Ice Cap. The core time scale, established using 137Cs and palaeomagnetic techniques, spans an estimated 600 years. A multi-proxy approach was used to document changes in the physical, chemical, and biological properties of the sediments. We found evidence for a relatively warm period (mid/late 15th century to mid/late 16th century) during the early part of the ‘Little Ice Age’ (LIA), characterized by high sedimentation rates and laminations. This was followed by colder, drier, and windier conditions corresponding to the coldest phase of LIA and coinciding with the latest and most extensive period of regional ice cap expansion (early 16th to late 19th centuries). A rapid warming occurred at the beginning of the 20th century. Variations in titanium (Ti) content in the core, a proxy for detrital sediment inputs, showed good agreement with reconstructed secular variations in summer melt rates on Penny Ice Cap between the mid-14th century and the present-day, providing supporting evidence for a climatic–hydrological connection between the ice cap and Nettilling Lake.
In order to elucidate the effect of recent warming, we studied lipid biomarkers and trace elements in a dated sediment core from Lake Heihai, a small, deep, and ultraoligotrophic alpine lake in Yunnan Province (SW China), being only marginally affected by anthropogenic activities. The variation in lipid biomarkers (such as 10-methyl-C16:0 fatty acid (FA), iso-branched C15 (i-C15) and anteiso-branched C15 (ai-C15) FA, and tetrahymanol) suggests a rapid productivity increase in sulfate reducing bacteria and ciliates since 1980, likely reflecting expansion of the hypolimnion anoxia and a prolonged duration of an oxic–anoxic chemocline in the water column. The concentrations of element molybdenum (Mo) in pre-1980 sediments approach the values in average crust. After 1980, the concentration increased, reaching levels approximately sixfold higher than the initial abundances. This likely reflects a high authigenic Mo deposition when the bottom water was more anoxic and enrichment in H2S. The suggested spatial and temporal expansion of the anoxic bottom water since 1980 was probably a response to the regional climate warming, resulting in stronger water column stratification and terrestrial grass inputs to the lake, and thus higher dissolved oxygen (DO) loss in hypolimnion.
The chronology of the extinction of the Balearic fossil bovid Myotragus balearicus in Mallorca and Menorca has been under discussion since its discovery in 1909, and especially in the last decades, thanks to the radiocarbon dates that have been obtained from several deposits of the island of Mallorca. Here, we present new radiocarbon dates of M. balearicus bones (including the most recent date ever obtained for the species, 4035 ± 32 BP, 2830–2470 cal. BC) that together with a newly published radiocarbon date for the evidence of the first human presence in the island (introduced Caprinae bone, 3884 ± 36 BP; 2470–2210 cal. BC) allow us to reduce the uncertainty period for the Myotragus extinction (UPME) in Mallorca from 1660 to 620 years (p > 95%) or even to 350 years (p > 90%) and to reject the hypotheses suggesting a climate change–driven (i.e. non-human) extinction of the species. This new scenario points to the causal relationship between the first human arrival and the M. balearicus extinction. The chronological gap between the earliest documented M. balearicus and the first documented human presence represents one of the shortest time periods documented between endemic megafauna and humans on any Mediterranean island.
Morphological analysis of plant remains from archaeological sites provides evidence regarding the domestication process of crop species, and the changing economic behaviors of humans during the foundation and intensification of agriculture. In contexts from the Neolithic and early state periods of Henan, China, morphometry of genus Setaria millet seeds is shown to provide data on production versus consumption contexts of archaeological deposits, in connection with site function and settlement hierarchy. Comparative morphometry of modern Setaria seeds sheds light on larger archaeobotanical issues, including problematizing the distinction between domesticated and wild/weedy seeds. Statistical analysis suggests that subdivision of archaeological millets below the genus level is less useful in some cases than consideration and comparison of genus-level populations.
Recent research has demonstrated that a series of mountains from the eastern Iranian Plateau to eastern Kazakhstan and to western China played a significant role in trans-Eurasian exchange during the third and second millennia BC. In close association with these mountain corridors, a number of southwestern Asian cereals, notably free threshing wheat and barley, moved eastward, and broomcorn millet, among other plant foods originating in China, moved westward. In this paper, we apply Bayesian stable isotope mixing models to published and newly obtained isotopic data in order to quantitatively estimate the contribution of different food resources to human diets, and we consider the complexity of human food strategies at both ends of these mountain corridors: southern Kazakhstan and the Hexi Corridor in western China. Our results contrast the rapid adoption of wheat and/or barley in the Hexi Corridor with the gradual, incremental adoption of millet in southern Kazakhstan during the second millennium BC.
The Sechura Desert provides a unique example of a vast palaeo-lagoon system on the Peruvian coast that was active during the first millennium AD. Reconstruction of coastal evolution is made possible by the good resolution of the sedimentary records of the Las Salinas Noroeste coastal plain. Evidence from morphostratigraphy and sedimentary facies indicates marked environmental diversity between the 3rd and the 8th centuries AD and a wide variability of sedimentary dynamics: lagoon foreshores received alternately fine distal marine sediments and coarser continental sediments in pro-deltaic sheets. Evaporation phases periodically occurred in these foreshores causing the formation of salt crusts. After a last high water level in the 8th century AD, the lagoon ultimately dried out and remains dry today. The malacofauna and sedimentary facies indicate that marine marshes bordered by vegetation, perhaps mangrove, developed in the higher parts of these lagoons. This palaeogeography is explained by the progressive build-up of a sand bar which started at least in the middle Holocene. From the 3rd to 8th centuries AD, the lagoon had limited connection to the sea in its northern end and hosted a warm-water and productive ecosystem that was exploited by pre-Hispanic populations. Wetter conditions in the Andes and occasional El Niño rainfalls maintained the lagoon during this period. The freshwater input likely stopped in the 8th century AD, which led to the closing of the shore bar under the influence of the longshore drift rapidly followed by the drying up of the lagoon, and the abandonment of the archaeological site.
An archaeological dimension expands the concept of biodiversity by generating long-term perspectives, combining multiple approaches and methodologies to enhance understanding of environmental changes. Aiming to investigate the patterns of biodiversity of marine mollusks over time, a comparison was made between three sets of archaeological sites (shellmounds) located in three geographic areas of the south-southeastern Brazilian coast. Sites dated between 1000–2000 and 4000–5000 yr BP were analyzed. A total of 37 bivalves and 26 gastropods were recorded. To describe the malacological community two indices of taxonomic diversity were used: average taxonomic distinctness and variation in taxonomic distinctness. The results showed a tendency of reduction in biodiversity patterns in the last 5000 years measured as average taxonomic distinctness. The observed reduction in biodiversity does not seem to be directly related to climate change over the period and there is a lack of data which could demonstrate any association between reduction in biodiversity and cultural causes such as preferences, technical level or food taboos of the prehistoric human populations. On the other hand, changes in sea level during this period are well documented and have been responsible for dramatic changes along the coast of this region. Therefore, it is likely that it could have affected local biodiversity and caused the observed pattern.
The Transural steppe is a cultural contact zone between areas east and west of the Ural Mountains. Mobile pastoralism is the traditional way of life in the steppe, while sedentary cultures constitute an exception, probably as a result of climatic variations. A change of lifestyle together with other innovations is documented at the turn of the 3rd to the 2nd millennia BC and often believed to have been accompanied by a shift to agro-pastoralism. To examine the ecology and economy in the Bronze Age steppe, we employed a combination of methods. As proxy-data, plant macro-remains from archaeological excavations of Sintashta fortified settlements and pollen from off-site archives were used for a high-resolution palaeoenvironmental reconstruction. Statistical comparisons of past and present pollen spectra show no significant differences in vegetation distribution. This allowed us to map the recent vegetation units by multispectral satellite imagery and to use them for modelling. Models further incorporate steppe productivity, carrying capacity and population figures to estimate herd sizes. Even if the climate was suitable for agriculture, evidence is missing from all botanical records. The economic mainstay was animal husbandry. Models consider autonomous activity zones of at least 4 km radius surrounding each Sintashta settlement where grazing resources could easily sustain the estimated population and their livestock. The river is seen as the determining factor to settle in this region as it provided constant access to water and valuable natural grazing areas. During dry years and winter, the productive meadow steppes functioned as reserve pastures.
A total of 51,074 archaeological sites from the early Neolithic to the early Iron Age (c. 8000–500 BC), with a spatial extent covering most regions of China (c. 73–131°E and c. 20–53°N), were analysed over space and time in this study. Site maps of 25 Chinese provinces, autonomous regions and municipalities, published in the series ‘Atlas of Chinese Cultural Relics’, were used to extract, digitalise and correlate its archaeological data. The data were, in turn, entered into a database using a self-developed mapping software that makes the data, in a dynamic way, analysable as a contribution to various scientific questions, such as population growth and migrations, spread of agriculture and changes in subsistence strategies. The results clearly show asynchronous patterns of changes between the northern and southern parts of China (i.e. north and south of the Yangtze River, respectively) but also within these macro-regions. In the northern part of China (i.e. along the Yellow River and its tributaries and in the Xiliao River basin), the first noticeable increase in the concentration of Neolithic sites occurred between c. 5000 and 4000 BC; however, highest site concentrations were reached between c. 2000 and 500 BC. Our analysis shows a radical north-eastern shift of high site-density clusters (over 50 sites per 100 x 100 km grid cell) from the Wei and middle/lower Yellow Rivers to the Liao River system sometime between 2350 BC and 1750 BC. This shift is hypothetically discussed in the context of the incorporation of West Asian domesticated animals and plants into the existing northern Chinese agricultural system. In the southern part of China, archaeological sites do not show a noticeable increase in the absolute number of sites until after c. 1500 BC, reaching a maximum around 1000 BC.
Over the past decade, researchers have directed greater focus toward understanding Bronze (3200–800 BC) and Iron Age (800 BC–AD 400) economies of Central Asia. In this article, we synthesize paleobotanical data from across this broad region and discuss the piecemeal archaeological evidence for agriculture in relation to environmental records of vegetation and climate change. The synthesis shows that agricultural products were present in northern Central Asia by the mid-3rd millennium BC; however, solid evidence for their spread even further north into the Altai Mountains and southern Siberia only comes from the late 2nd and early 1st millennia BC. The earliest crops introduced into Central Asia likely came as a mixed package of free-threshing wheat, naked barley, and broomcorn millet, an assemblage pioneered further south along the northern foothills of the Central Asian mountains. Further east, in Mongolia, and debatably to the west of Central Asia, in the steppe of northern Kazakhstan and the southern Ural region of Russia, the earliest evidence of agriculture (with a similar mixed assemblage) is considerably later, roughly late 1st millennium BC. The lack of clear-cut early evidence for agricultural goods either east or west of the Central Asian mountain belt suggests that agriculture spread northward along these mountains, based on an agropastoral system pioneered millennia earlier at higher elevations of lower latitudes. Additionally, moister regional environmental conditions in the northern mountains after 3000 cal. BC may have increased the favorability of adopting an agricultural component in the economy.
Pollen and charcoal records derived from the sediment core of Lantianyan (LTY) peat bog, Northern Wuyi Mountain chains, eastern subtropical China, provide valuable information of landscape evolution caused by both climatic variation and anthropogenic activities over the past 8200 years. Our results reveal fluvial and lacustrine deposition between c. 8200 and 5600 cal. yr BP. The high proportion of pollen from evergreen broadleaved forests (e.g. Quercus and Castanopsis) and Alnus trees, a taxon frequently occurring in mountain wetlands, implies a humid interval, which is consistent with the Holocene moisture maximum in eastern China. After 5600 cal. yr BP, the spread of the wooded swamp taxon, Glyptostrobus, suggests shallow water conditions and peat formation caused by gradual drying. The drying trend generally corresponds with the speleothem isotope record from this region, revealing a weakening East Asian summer monsoon (EASM) due to a decrease in Northern Hemisphere summer insolation (and in air temperature). Peaks in the abundance and concentration of Glyptostrobus pollen at c. 4600–4400 cal. yr BP and c. 3300–3000 cal. yr BP suggest two periods of swamp expansions, which coincide with the drought intervals revealed by the speleothem records. The LTY pollen and charcoal record demonstrates that human-induced land cover change was negligible before 3600 cal. yr BP. We consider the first signal of intensive human activity and landscape clearing to be the noticeable increase in charcoal particles at around 3600 cal. yr BP. This anthropogenic impact is followed by a dramatic decrease in arboreal pollen and increase in Poaceae pollen percentages, likely reflecting a transition to rice-paddy agriculture in the study area.
Rebun Island with Hamanaka and Funadomari among the 43 documented archaeological sites and the environmental archive stored in the Lake Kushu sediment proves to be one of the key areas to study the interplay between ecology, climate and human activities. This paper focuses on the potential of palaeobotanical records from Rebun Island for improving the chronological control and understanding of late Quaternary climate changes and habitation environments of northern hunter-gatherers in the Hokkaido Region of Japan. A set of 57 radiocarbon dates of the RK12 core (Lake Kushu) demonstrates that it represents a continuous environmental archive covering the last c. 17,000 years. The RK12 pollen record reflects distinct vegetation changes associated with the onset of the lateglacial warming about 15,000 cal. yr BP and the cold climate reversal after c. 13,000 cal. yr BP. The onset of the current Holocene interglacial after c. 11,700 cal. yr BP is marked by a major spread of trees. The middle Holocene (c. 8000–4000 cal. yr BP) is characterized by a major spread of deciduous oak in the vegetation cover reflecting a temperature increase. A decline of oak and spread of fir and pine is recorded at c. 2000 cal. yr BP. After c. 1100 cal. yr BP, arboreal pollen percentages decrease, possibly linked to intensified usage of wood during the Okhotsk and Ainu culture periods. The results of diatom analysis suggest marshy or deltaic environments at the RK12 coring site prior to c. 10,500 cal. yr BP and a brackish lagoon between c. 10,500 and 7000 cal. yr BP. A freshwater lake developed after 6500 cal. yr BP, likely reflecting sea level stabilization and formation of the sand bar separating the Kushu depression from the sea. Plant macrofossil analysis shows use of various wild plants and also domesticated barley during the Okhotsk and Ainu periods.
The spatio-temporal distribution of archaeological sites in the Hokkaido region reveals hunter–gatherer population dynamics from the Upper Palaeolithic (>14,000 cal. yr BP) through the Neolithic/Jomon and Epi Jomom period (c. 14,000–1300 cal. yr BP) to the historic Ainu period (c. 700–100 cal. yr BP). It appears that most cultural transitions coincide with periods of climate and environmental change. However, this observation does not automatically mean causality and, therefore, other potential driving factors must be checked. The data support the hypothesis that Palaeolithic subsistence was (at least partly) based on terrestrial hunting. Paralleled by lateglacial climate amelioration, rising sea levels and a change in marine currents, this strategy shifted towards marine resources and plant exploitation at the beginning of the Jomon period. Along with continuous Holocene climate warming, Hokkaido’s Neolithic Jomon population increased culminating in the Middle Jomon period (5000–4000 cal. yr BP). Simultaneously, Jomon subsistence underwent a process of diversification and intensification in exploitation of food resources. This practice probably allowed the persistence of the Middle Jomon culture beyond the Holocene temperature optimum (around 5000 cal. yr BP). Thereafter, the population decreased until the end of the Jomon culture accompanied by a trend towards cooler climate conditions and a shift in subsistence towards a more narrow range of food resources with increased hunting and less plant food. Population re-increased during the Satsumon/Okhotsk culture periods (1500–700 cal. yr BP), which may be the result of Okhotsk immigration because of climate cooling in the regions north of Hokkaido and enhanced inner-Hokkaido trade (between Satsumon and Okhotsk) and trade with communities outside Hokkaido. During the Ainu period (c. 700–100 cal. yr BP), site, and possibly population numbers, re-decreased significantly and concentrated in eastern Hokkaido. Whether social and/or climatic factors brought about the Satsumon–Ainu cultural transition and the observed change in population pattern remains unresolved.
The timing of landscape change, post-settlement alluvium (PSA) deposition and gully erosion in the southeastern Australian Tablelands remains at the centre of a long-standing discussion over the geomorphological effects of European land-use compared with Aboriginal land-use and climate change. Few quantitative studies date the onset of gully erosion and subsequent PSA deposition in the Tablelands and those that do determine the timing of landscape change for individual catchments rather than across the region. In this study, we present optically stimulated luminescence (OSL) burial ages of swampy meadow (SM) sediment and PSA from six sites spread throughout the Goulburn Plains to place better regional constraints on the timing of landscape change. PSA burial ages at each of our sample sites range between 213 and 81 years before AD 2013, the year during which all samples were collected and measured – corresponding to AD 1800–1932. All measured PSA burial ages post-date European arrival to Australia and are therefore consistent with the generic name and implied age assigned to these sediments before quantitative age estimates were available for them. We suggest, however, that the term ‘post-European settlement alluvium’ may be more appropriate in the Australian context as Aboriginal Australians were living in the Tablelands prior to European arrival. Associations between the occurrence of gully incision and PSA deposition throughout the Tablelands and climatic factors are tenuous, and we suggest that European land-use practices in the region dominate landscape evolution, which had been driven by climatic factors throughout the Holocene.
Agricultural societies around the world have dramatically altered the natural landscape, particularly through accelerated soil erosion. The expansion of agricultural land use into steeper headwater areas during the Medieval period in central Europe is known to have caused large increases in soil erosion and sediment redistribution downstream. Although land-use practices changed and improved following this initial impact, it is currently unknown whether changes in land-use techniques also improved hillslope soil erosion and sediment redistribution rates. In this paper, we use a variety of techniques, including chrono-stratigraphy, wood charcoal analysis and a geostatistical model, to reconstruct land-use and erosion rates for the period spanning the Medieval Period to the present (1100–300 years ago) in a small headwater catchment in central Europe. Coupling land-use, hillslope erosion and sediment redistribution fluxes, we find the largest flux change occurs because of the initial deforestation at the beginning of the Medieval Period (1100 years ago). Following deforestation, we identified three main types of land-use techniques that were practised between ~1100 and 300 years ago: Horticulture, cropping agriculture and rotational birch silviculture, the last of which represents the earliest evidence for this practice found in central Europe to date. However, we find only small differences in hillslope fluxes throughout the catchment despite the variable land-use techniques employed. This is because the land-use techniques primarily influenced and increased the hillslope sediment storage capacity rather than erosion rates directly, which is an important distinction to consider for future work attempting to link changes in human land use and hillslope erosion.
This study presents the results of a multi-proxy analysis conducted to improve our understanding of the palaeoenvironmental conditions of the freshwater and brackish marshes of Cal Maurici (Barcelona, Spain) and the human impact on them during the mid-Holocene (6171–3891 cal. yr BP). The study integrates data from pollen, phytolith, diatom, charcoal, seeds and malacological analyses and helps to reconstruct the ecological conditions during the early establishment of farming communities in western Mediterranean facade. The results indicate a landscape dominated by Mediterranean vegetation with aquatic plants in the shallow marshes and well-developed forests in the nearby area, providing for the first time in the Holocene of NE Iberian Peninsula the palaeoecological conditions of deltaic areas. Ecofactual evidence indicates an initial landscape dominated by brackish marshes (6171–5773 cal. yr BP) in which Ruppia cf. maritima was predominant and human impact was low. Between 5026 and 4839 cal yr. BP, freshwater conditions expanded with an increase in Potamogeton sp. and the presence of Typha angustifolia and Spirogyra sp. algae with well-developed oak woodlands and deciduous trees in nearby areas. The expansion of evergreen forest occurred later (from 4960 to 4825 cal. yr BP until 3712 cal. yr BP), with the decline of deciduous woodland and the expansion of evergreen oaks, pinewoods, wild olive trees and box, coinciding with a period of increased human activity in the area. Additionally, the presence of marine resources at several archaeological excavation sites and domestic plants at Cal Maurici provides an opportunity to evaluate the interaction between earlier farmers and marine or deltaic ecosystems.
As heated debates about the origin of rice domestication and cultivation in southern and eastern China continuously attract attention of the broad scientific community, new evidence for early rice exploitation from the regions located outside the core area of domestication, the lower Yangtze, are very important. Here, we present new archaeobotanical results of plant macrofossil and phytolith analyses, including directly dated rice grains from the sites of Dongpan (4030–3820 cal. BC) and Beiqian (3700–2900 cal. BC). These results fill (at least partly) an existing gap between the c. 8000-year-old rice remains from the Early Neolithic Houli Culture (c. 6500–5500 BC) sites north of the Shandong Highlands and the Longshan Culture (c. 2600–1900 BC) sites, where intensive rice agriculture was practiced. Neither rice nor millet made substantial contribution to the plant macrofossil assemblage at Dongpan, while broomcorn (and to a lesser extent foxtail) millet contributed up to 75% to the macrofossil assemblage at Beiqian. This increase can be interpreted as a major change in regional subsistence from strongly relying on wild resources and small scale cultivation during the Beixin Cultural period to a millet-based economy during the Dawenkou Culture.
The two East Asian millets, broomcorn (Panicum miliaceum) and foxtail millet (Setaria italica), spread across Eurasia and became important crops by the second millennium BC. The earliest indisputable archaeobotanical remains of broomcorn millet outside of East Asia identified thus far date to the end of the third millennium BC in eastern Kazakhstan. By the end of the second millennium BC, broomcorn millet cultivation had spread to the rest of Central Eurasia and to Eastern Europe. Both millets are well suited to an arid ecology where the dominant portion of the annual precipitation falls during the warm summer months. Indeed, the earliest sites with millet remains outside of East Asia are restricted to a narrow foothill ecocline between 800 and 2000 m a.s.l., where summer precipitation is relatively high (about 125 mm or more, from May through October). Ethnohistorically, millets, as fast-growing, warm-season crops, were commonly cultivated as a way to reduce agricultural risk and were grown as a low-investment rain-fed summer crop. In Eurasian regions with moist winters and very low summer precipitation, the prevailing agricultural regime had long depended on winter wheat (Triticum aestivum) and barley (Hordeum vulgare) cultivated with supplemental irrigation. We propose that the secondary wave of millet cultivation that spread into the summer-dry regions of southern Central Asia is associated with an intensification of productive economies in general, and specifically with the expansion of centrally organized irrigation works.
Geomorphologic, stratigraphic, faunistic, palynological and 14C analyses were carried out in the area of the mouth of the Garigliano River characterized by two strand plains that are referred to the Eutyrrhenian and the Holocene, rimming two depressed zones separated by the Garigliano River channel. This study depicts the palaeoenvironmental evolution over the last 8200 years and the landscape context at the time of Minturnae Roman colony. Between 8200 and 7500 yr BP, a wet zone occurred in the northern zone, whereas in the southern part, a lagoon developed. During the final transgression stage and the beginning of the sea level still stand (7500–5500 yr BP), a freshwater marsh formed in the northern zone, and the width of the southern lagoon decreased. Between 5500 and 3000 yr BP, the coastal barrier changed into a delta cusp, a freshwater marsh also appeared in the southern part and the river wandered between the twin marshes. Because of local uplift, previously unknown in this area, part of the floor of the southern marsh emerged, and after 4000 yr BP, both marshes became coastal ponds with prevailing clastic sedimentation. A progressive increment in anthropic forcing on the land took place after 3000 yr BP. The Marica sanctuary was built (7th century BC), and the Roman colony of Minturnae was developed beginning the 3rd century BC. The shallow depth of the ponds prevented their use as harbours, and saltwork plants can be ruled out based on the faunal and palynological data. The ongoing infilling of both ponds was never completed, and their reclamation is still in progress.
A number of informal terms (e.g. Anthropocene, Anthropozoic, Psychozoic, Noozoic, and Technogene) have been used to designate the rock unit and time interval where the impact of collective human action on the Earth system is clearly recognizable (called here the Humanized Earth System (HES)). Presently, Anthropocene is the most commonly used, and the International Commission on Stratigraphy is considering its acceptance as a formal stratigraphic unit. Despite their informal character, all of these terms contain suffixes (i.e. -cene, -zoic, or -gene) that define formal chronostratigraphic/geochronologic (C/G) units (e.g. series/epoch, erathem/era, and system/period), which is misleading. In addition, the use of these terms involves unsupported evolutionary assumptions and may lead to conflicting stratigraphic settings. Therefore, it is recommended that these terms are avoided until there is sufficient scientific support to unequivocally define its C/G rank, which is not expected to occur in the near future.
Radiocarbon-dated spring-fed fen deposits from the Komarów site (Volhynia Upland, SE Poland) with its multi-proxy data (macrofossils, molluscs, geochemistry, pollen, stable isotopes of oxygen and carbon) enable us (1) to distinguish four main stages of fen evolution, which reflected a distinct variability of water supply conditions and (2) to reconstruct the Holocene humidity–temperature changes. The beginning of peat–tufa deposition took place in a Boreal phase, after a significant cool fluctuation of climate occurring ca. 9.4 ka cal. BP. We suggest that climate was the most important factor conditioning the development of the spring-fed fen. Permafrost degradation, and then wet periods, intensified the activity of ascending springs. The impact of humans was possible since the Neolithic period and increased during the Middle Ages: therefore, the anthropogenic influence could have partially overlapped with the regional tendencies of climate changes. Autogenic development of deposit succession in the studied fen was definitely conditioned by hydrological changes induced by climate. Based on the multi-proxy data, 12 cold events of different ranks were identified. They are also recorded in other Polish and European sites. A record of distinct variability of depositional conditions at ca. 9.4, 8.2, 5.9, 4.6, 2.8, 1.4 and 0.55 ka cal. BP corresponds to quasi-periodical global climate changes in the Holocene named the Bond events. The majority of the cold events recorded in 13C and 18O of carbonates can be correlated to the Greenland oxygen isotope curve.
New detailed palynological and ostracodological analyses together with texture data from a sediment core drilled in Ostia Antica confirm the existence of the ancient Ostia harbour and its location by the Tiber River. Using the different proxies analysed in this work and chronologically framing the sediment record with three AMS radiocarbon dates, four phases have been singled out: pre-harbour, harbour bay under fluvial influence, more protected harbour basin and post-harbour phase. Ostracodology is used to reconstruct the marine versus freshwater influence in the basin. Palynology is used to reconstruct the plant landscape and the surrounding environment. Phases with low pollen concentration and expansions of NPPs suggest soil erosion and are alternated with quieter ones, where human impact was very clear. Deciduous oaks typical of coastal plain forests are the main taxon during the harbour phases. The occurrence of riparian trees increases in periods with low pollen concentration, high NPPs and very high pine percentages. These should be the periods in which important sediment inputs inside the harbour basin arrived and could be the expression of intense flooding phases. The comparison between the ostracod assemblages recovered in the two cores and has led to speculate a complex harbour structure. A separation could explain the micropalaeontological differences between the cores. Thus, we suggest that a pier must have been built in order to protect the inner harbour from the marine influence and to unload the goods transported by the big ships.
Major Mediterranean deltas began to develop during a period between 8000 and 6000 yr BP when the rate of fluvial sediment input overtook the declining rate of sea-level rise. However, different authors have argued that the Ebro Delta primarily formed during the late Middle Ages as a consequence of increased anthropogenic pressure on its river basin and these arguments are supported by the scarcity of previous geological studies and available radiocarbon dates. To reconstruct the environmental evolution of the Ebro Delta during the Holocene, we used micropalaeontological analysis of continuous boreholes drilled in two different locations (Carlet and Sant Jaume) on the central delta plain. Different lithofacies distributions and associated environments of deposition were defined based on diagnostic foraminiferal assemblages and the application of a palaeowater-depth transfer function. The more landward Carlet sequence shows an older and more proximal progradational delta with a sedimentary record composed of inner bay, lagoonal and beach materials deposited between 7600 and >2000 yr BP under rising sea-level and highstand conditions. This phase was followed by a series of delta plain environments reflected in part by the Carlet deposits that formed before 2000 yr BP. The Sant Jaume borehole is located closer to the present coastline and contains a much younger sequence that accumulated in the last 2.0 ka during the development of three different deltaic lobes under highstand sea-level conditions. The results of this study reinforce the idea that the Ebro Delta dates to the early Holocene, similar to other large Mediterranean deltas.
In this study, we reconstruct the recent environmental evolution of the inner Cadiz Bay using sedimentary records reaching back as far as AD 1700. We report lithological descriptions of the sediments and extensive mineralogical and geochemical analyses. An extraction technique that identifies different Fe phases provides an assessment of diagenetic alteration, which allows an estimation of the original organic matter inputs to the inner Cadiz Bay. Downcore variations in Corg/N ratios, 13Corg and 15N are related to changes in organic matter sources and the trophic state of the water column. The downcore records of selected trace metals (e.g. Pb, Zn and Cu) are interpreted to reflect changes in heavy metal pollution in the bay, while records of other elements (e.g. Mn and P) are likely overprinted by diagenetic alteration. Major environmental shifts took place during the 20th century, when the population around Cadiz Bay increased exponentially. Increases in sediment accumulation rates, organic matter inputs and heavy metal contents, in parallel with increases in 13Corg and 15N over this period, are interpreted as direct effects of the increasing anthropogenic influence in the area. The results of this study suggest that multiproxy approaches and detailed consideration of diagenetic overprinting are required to reconstruct past environmental conditions from coastal sediments.
The arid climate of many regions within Central Asia often leads to excellent archaeological preservation, especially in sealed funerary contexts, allowing for ancient DNA analyses. While geneticists have looked at human remains, clothes, tools, and other burial objects are often neglected. In this paper, we present the results of an ancient DNA study on Bronze Age leather objects excavated from tombs of the Wupu cemetery in the Hami Oasis and Yanghai cemetery in the Turpan Oasis, both in Xinjiang Uyghur Autonomous Region of northwestern China. In addition to species identification of goat (Capra aegagrus/hircus), sheep (Ovis orientalis/aries), and cattle (Bos primigenius/taurus), mitochondrial haplogroups were determined for several samples. Our results show that Bronze Age domesticated goats and sheep from the Hami and Turpan oases possessed identical or closely related haplotypes to modern domestic animals of this area. The absence of leather produced from wild animals emphasizes the importance of animal husbandry in the cultures of Wupu and Yanghai.
In an effort to reconstruct past aeolian activity, a foredune stratigraphy and a continuous lake sediment record from the largest dunefield on Andøya, northern Norway, have been investigated. The dunefield extends landwards in a north-eastward direction and consists of several parabolic dunes, foredunes and blowouts. The sediment record (169 cm) from the nearby lake Latjønna and the foredune stratigraphy (10 m) covers the last 6200 and 3700 cal. yr BP, respectively. Both sites possess sediments deposited after the Tapes transgression maximum (~6800 cal. yr BP), which reached a level of ~7–8 m a.s.l. at the study site. The lake sediment record consists of several units dominated by sand grains interspersed by more organic-rich beds. The core has been examined by x-ray fluorescence (XRF), magnetic susceptibility (MS) and loss-on-ignition (LOI). Mineral grains were detected by wet sieving of the ignition residue (IR), and the influx of sand grains to Latjønna was calculated based on the weight of sand grains >250 µm/cm divided by the accumulation rate determined from a radiocarbon (14C)-based age–depth model. Phases with high influx of sand to Latjønna are recorded around 4800, 4250, 3000–2000, 1850–1750, 1600–600, 450, 300 and 150 cal. yr BP, which coincides with periods of increased storminess recorded in other studies around the North-Eastern Atlantic region. The two study sites show, however, quite contrasting results; high sedimentation rates in the lake record associated with greater aeolian influx correspond to stability in the foredune stratigraphy reflected by the presence of several palaeosols. Because of this out-of-phase behaviour, it is suggested that the foredune is mainly influenced by summer climate and relative sea level (RSL) change, whereas the lake record is more influenced by niveo-aeolian processes transporting sand grains farther inland during winter.
Coastal environments of the early mid-Holocene provided challenges and opportunities for agriculturalists living in the Santa Elena Peninsula, Ecuador (Santa Elena Province, formerly southwestern Guayas Province). Cores extracted from swamps in three river outflows, namely, the Río Verde/Río Zapotal drainage (Chanduy estuary), the Río Grande (Punta Carnero locality), and the Río Valdivia, provided pollen, phytolith, sedimentary, and elemental sequences relevant to documenting vegetation and agriculture. The Chanduy record documented maize and other cultigens from 3200 to 500 cal. BC, providing evidence for intensive cultivation of alluvial lands. The Punta Carnero core provided the first evidence for occupation of the peninsula during the ‘hiatus’ between the Vegas and Valdivia periods, as maize was present in a stratum dating to 4857 cal. BC. Records documented mid-Holocene sea-level stabilization, development of low-energy depositional environments, and variation in rainfall attributable to El Niño-Southern Oscillation (ENSO) by 5000 cal. BC. There was no evidence that the region was either markedly wetter or drier in the early mid-Holocene, suggesting that climate controls similar to those of today were in place.
In this paper, we present high-resolution early Holocene pollen, plant macrofossil, charcoal, diatom, biogenic silica, and loss-on-ignition records from a mountain lake in the South Carpathians in order to reveal ecosystem response to the 8.2-ka climatic oscillation. We found significant changes both in terrestrial vegetation and lake diatom assemblages in the northern slope of the Retezat Mts between c. 8300 and 8000 cal. yr BP. Rapid changes in relative frequencies and pollen accumulation rates of the major deciduous pollen types associated with peaks in microcharcoal accumulation rates suggested that vegetation disturbance mainly took place in the mixed-deciduous forest zone, where woodland fires partially destroyed the populations of Fraxinus excelsior, Quercus, and Corylus avellana and facilitated the establishment of Carpinus betulus in the forest openings. The diatom record furthermore showed the spread of a planktonic diatom species, Aulacoseira valida, at 8150 cal. yr BP, coincidently with a short-lived expansion of C. betulus. Since diatom blooms mainly occur in spring in the Retezat Mts, increased spring water depth and increased water turbulence were inferred from these data. The expansion of C. betulus against F. excelsior and C. avellana at the same time suggested a modest increase in available moisture during the growing season. Taken together, these data imply that during the 8.2-ka event, winter and spring season available moisture increased, while summers were characterized by alternating moist/cool and dry/warm conditions.
The ‘Cape Flats’ region, situated in the winter rainfall zone of South Africa, is a low-lying tombolo underlain by recent fluvial and aeolian sands and characterised by numerous small lakes and wetlands. One of these is Princessvlei, a eutrophic, freshwater coastal lake. The lake lies in an inter-dunal depression encroached on in the more recent past by high-density residential, industrial and agricultural land uses. A 210-cm core extracted from the lake periphery yielded high diatom fossil concentrations for the upper 174 cm. Princessvlei appears to oscillate between two ecologically stable states, namely, a state characterised by clear water, oligotrophic, benthic communities and a turbid state dominated by eutrophic, planktonic species. The two stable ecological states are interpreted to be a function of the relative dominance of catchment precipitation or groundwater influx which augments the open water conditions. From 2600 to 1500 cal. BP (173–135 cm), the system is predominantly turbid with greater moisture availability before a relatively rapid development of oligotrophic and dilute conditions from 1300 to 610 cal. BP (135–30 cm). A brief period of deeper water depths and meso-eutrophic conditions is observed between 550 and 445 cal. BP (23–13 cm). Following a short-lived hiatus, poly-hypertrophic, alkaline species are abundant in the top 10 cm coinciding with European colonisation in the region from the 17th century.
Records of occupation by humans in the period following shortly after the Last Glacial Maximum (LGM; 21 ± 2 kyr cal. BP) are still very rare in Central Europe, since it is inferred that the extreme climatic conditions caused the decolonisation of previously settled areas. Our study focuses on the reconstruction of environmental conditions in the surroundings of the open-air Palaeolithic site, Brno-Štyřice III, which falls within this period. The research concentrated on the study of malacological, pollen and anthracological samples to reconstruct the climate shortly after the LGM. 14C dating places the chronostratigraphic position of the site more precisely at the end of the LGM, more specifically into Last Glacial Termination (LGT); analysis of chipped stone industry identifies the occupation with the Epigravettian settlement. The site represents a significant example of the recurrent habitation of a microclimatically favourable microregion near a watercourse in order to utilise available sources of livelihood. The results of the pollen, anthracological and malacological analyses documented a more or less treeless character of surrounding landscape. The vegetation was mostly formed by a mixture of shrub tundra and grassy loess steppe vegetation. Open woodland with birch, willow and bird cherry occurred in relatively moist river banks and the lower slopes of hills with more favourable microclimatic conditions. Malacological collection highlights the presence of cool temperate species (Pupilla loessica, Vallonia excentrica and Helicopsis striata). In the surroundings of the studied site, the pollen analysis provided a reconstruction of parkland forest-steppe vegetation (with lack of temperate deciduous trees) typical for a cold and dry climate. Development of both dry and moist stands near the watercourse was recorded. Anthracological analysis is in support of similar outcomes, reconstructing the presence of open woodland with dominating birch and willow in the nearby surroundings.
A major assemblage of Mesolithic and Neolithic wooden artefacts has been recovered from the bed of the River Užava at Sise, in the coastal belt of western Latvia. New archaeological investigation has also produced wooden remains and other evidence of occupation on the riverbank. On the basis of multi-proxy environmental data and radiocarbon dating, this article offers a first attempt to place the human activity in a palaeolandscape context. The earliest evidence of human presence is provided by wooden artefacts dated to c. 10,500–9700 cal. BP, during the Ancylus Lake transgression. These remains are thought to reflect fishing activities in the shallows of the Ventspils Bay, which existed during the transgression. The regression that followed brought a return to river-valley conditions at the site, and the next recorded period of human activity, evidenced by 14C-dated antler tool finds, is associated with the beginning of the Littorina Sea transgression, culminating c. 7500 cal. BP. With the formation of a new Ventspils Bay/Lagoon, the Sise site, at or near the river mouth, would have regained its status as an advantageous fishing location. Archaeological finds indicate continued human activity c. 6000–4000 cal. BP, even though the sea level was now lower and this was no longer a river-mouth location. Such a pattern of recurrent human occupation during the early to middle Holocene, associated with repeated shifts of the shoreline, appears to be characteristic of the central region of the Baltic Sea Basin.
The study of environmental change during the ‘Little Ice Age’ (‘LIA’) offers a great potential to improve our current understanding of the climate system and human–environment interactions. Here, a high-resolution multiproxy investigation of a Mediterranean mire from central-western Spain, covering the last ~700 years, was used to reconstruct peat dynamics and land-use change and to gain further insights into their relationship with ‘LIA’ climate (temperature and moisture). To accomplish this, concentrations and accumulation rates of major and minor lithogenic (Si, K, Ti, Rb and Zr) and biophilic (C and N) elements, as well as humification indices (UV-absorbance and Fourier-transform infrared spectroscopy (FTIR)) and pollen and non-pollen palynomorphs, were determined. Peatland dynamics seems to have been coupled to changes in solar irradiance and hydrological conditions. Our results point to wetter conditions after the mid-16th century, although with high intra-annual fluctuations. At the late 18th century, when solar activity was systematically higher than before, peat carbon accumulation rates (PCAR) showed a continuous increase and the humification indices suggest a change towards more humified peat. Enhanced soil erosion occurred at ~AD 1660–1800 (SE1), ~AD 1830–1920 (SE2) and ~AD 1940–1970 (SE3), although a minor increase in Si fluxes was also detected by ~AD 1460–1580. All phases coincided with higher abundances of fire indicators, but the changes recorded during the ~AD 1460–1580 event and SE1 coincide with the Spörer and Maunder minima, so a climatic influence on soil erosion cannot be discounted. Changes in the sources of mineral matter to the catchment between ~AD 1550 and ~AD 1650 and since the mid-17th century were likely related to modifications of tree cover and/or variations in wind strength.
Coring was carried out in a soligenous marsh in the Vosges Mountains in the past mining district of Sainte-Marie-aux-Mines (eastern France). High-resolution palynological, non-pollen-palynomorph, and geochemical analyses were performed along the core. Correlations between the herbal composition of the landscape and trace metals in the core reveal a specific palynological pattern during mining activities. Two main periods of anthropogenic impacts on vegetation and trace metal contamination are shown: during the 16th–17th centuries, for mining and smelting activities, and the beginning of the 20th century, for smelting and the Industrial Revolution. No drastic deforestations occurred near the study site, contrary to historical descriptions and prints of the valley. Controlled forest practices were implemented from the beginning of the record, that is, since cal. AD 1000, so the impact of mining activities seems to be less significant than expected near mining sites. We demonstrate that the minerotrophic characteristics of the record closest to past mining sites allows for (1) the description of the landscape associated with anthropogenic activities and (2) the recording of past trace metal emissions without post-depositional mobility.
Recent research in northern Iceland has highlighted a significant period of rock slope instability during the early Holocene due to the combined effects of postglacial rebound, relative sea-level fall, and glacially oversteepened mountain slopes. Using the Vatn landslide (Skagafjörður, central northern Iceland) as an example, this paper focuses on this period and describes the sequence of events that led to landsliding. Geomorphic mapping, stratigraphical evidence, and both radiocarbon and tephra dating were applied. Collectively, the data acquired indicate that the landslide occurred between 11,400 and 10,790 cal. yr BP. However, while rock slope failure represents a significant disintegration of mountain slopes, this study suggests that large postglacial landslides might also play a role in arresting sediment transport from other hillslope processes rather than contributing large volumes of sediment.
Fire is considered a major threat to forest conservation in the Neotropics. Palaeoecological studies are critical for understanding the long-term interactions of climate, fire, and human activities in the savanna–forest dynamic. Here, new data from palynological analyses conducted in sedimentary records from the northern edge of the Amazon Basin, the Gran Sabana, southeast of Canaima National Park (CNP) are presented. Four radiocarbon ages from Quebrada Kowana (QK) and two for Ariwe Fernland (AF) records showed that both are late-Holocene age (with extrapolated basal ages of 3100 and 3400 cal. yr BP, respectively). Both showed the occurrence of gallery forest until 1800 (QK) and 1600 (AF) cal. yr BP, with forest taxa reaching 60% and 40% of the terrestrial pollen sum, respectively. The main forest taxa were Celastraceae, Moraceae/Urticaceae, Schefflera, Protium, and Mahurea (QK) and Dimorphandra, Protium, Schefflera, Tachigali, and Blepharandra (AF). Savanna herbs (mainly Poaceae) reached 40–50% (QK) and 60% (AF). The high abundance of savanna herbs together with the low occurrence of mature forest taxa, and high abundance of pioneer taxa, suggests that the former forests comprised very open and disturbed forest-belts, surrounded by savannas. Since 1800 (QK) and 1600 (AF) cal. yr BP, forest taxa dropped to 10% and 5%, respectively, suggesting the substitution of forests by herbaceous communities. The high abundance of charcoal recorded from the beginning of the records to about 1800–1600 cal. yr BP suggests that recurrent fires spreading from neighboring savannas were reaching the former forest, causing compositional changes and triggering forest reduction. Fires were very likely human-made, but highly controlled by climate. Hence, forest substitution happened when a combination of local fires and droughts was given in every record. Results agree with those from other localities in the CNP in confirming the occurrence of regional-scale gallery forest degradation during the late Holocene.
Different political, economic, social and environmental factors are considered in plans for coastline reconstruction following tsunami events. These competing factors inevitably result in a compromise being made with respect to reconstruction policy and practice. Coastline reconstruction may also be constrained by availability of technology, speed of action or decision-making, local political expediency, and external influences such as disaster relief policy and the roles of NGOs. In some cases, it could be argued that such compromises result in inappropriate actions or decisions being taken that do not always consider the dynamics of coastal processes. An outcome is that expensive geoengineering structures may hinder long-term coastline recovery, and may result in future increased coastline vulnerability. Here, based on examples of the 2004 Indian Ocean and 2011 Tōhoku-oki tsunamis, we argue that inappropriate reconstruction after such events may have serious long-term negative effects that can contribute to increased future risk for inhabitants of tsunami-prone coastlines.
The Brazil Current (BC) is a relevant feature in the Atlantic Meridional Overturning Circulation (AMOC). Its behavior during slowdown or intense AMOC remains poorly known because of the lack of paleoceanographic records, especially for the Holocene. Here, we investigate changes in a western boundary upwelling system (Cabo Frio, off Southeastern Brazil) which are driven by variations in the BC and NE winds during the last 9 kyr. To assess the variability of the BC, we used 18O, Mg/Ca, and assemblages of planktonic foraminifera. Our results indicate five oceanographic phases during the last 9 kyr. During Phase I (from 9.0 to 7.0 cal kyr BP), the BC diverged offshore from the modern upwelling area because of the low sea level, increasing the influence of shelf waters and coastal upwelling plumes on foraminifera assemblages. Phase II (7.0–5.0 kyr BP) was marked by the approach of the internal front of the BC with low intensity and episodes of strong productivity that were linked primarily to the upwelling of the South Atlantic Central Water (SACW) and/or Subpolar Shelf Waters (SPSWs) (cold). Phase III (5.0–3.5 kyr BP) was a transition, marking a large oceanographic and climatic change from the weakening of the AMOC. The internal front of the BC became warm and subsurface SACW upwelling was stronger. In Phase IV (3.5–2.5 kyr BP), the BC acquired its modern dynamics, but weak NE winds weakened the SACW’s contribution to upwelling events. Finally, in Phase V (last 2.5 kyr BP), the NE winds reintensified, promoting frequent episodes of upwelling and intrusion by SPSWs during the Medieval Climate Anomaly.
It is still debated whether climate changes had an impact on the emergence, spread, and disappearance of early production-based (Neolithic) adaptations. To date, and despite the incorporation of various paleoclimatic proxies, there exists no spatial reconstruction of the regional impact of the North Atlantic cooling events on Central–Western European climate and environments during the early Holocene. In order to address these two issues, we estimated seasonal and annual temperature and precipitation from a marine pollen record from Trondheimsfjord (central Norway) along with 68 pollen records distributed across Central–Western Europe for the time period associated with the Linearbandkeramik (LBK) cultural tradition, 7600–6900 yr cal. BP. Two distinct vegetation-derived rapid, <100 years, climate changes, contemporaneous with reduced warm Atlantic water (AW) inflow and winter storminess in the northern North Atlantic, bracket the expansion of the LBK. The geographic expansion of LBK populations appears to coincide with winter warming by ca. 2.5°C on average, and an increase in summer and winter precipitation, while its decline is associated with decreases in winter temperature, by ~1.5°C on average, and summer rainfall. Our results confirm that LBK subsistence practices were well-adapted to wet and relatively warm winters and cool summers, which are favorable to some cultigens, such as einkorn. This is in contrast to the hypothesis that cooler and wetter climatic conditions would induce increased instability of agricultural communities leading to the decline of LBK populations.
Contemporary climate dynamics of the circum-Caribbean region are characterised by significant precipitation variability on interannual and interdecadal timescales controlled primarily by El Niño Southern Oscillation (ENSO) and the Atlantic Multidecadal Oscillation (AMO). However, our understanding of pre-industrial climate variability in the region is hampered by the sparse geographic distribution of palaeoclimate archives. Here, we present a high-resolution reconstruction of effective precipitation for Barbuda since the mid-16th century, based on biostratigraphic and stable isotope analyses of fossil ostracods and gastropods recovered from lake sediment cores from Freshwater Pond, the only freshwater lake on the island. We interpret episodic fluctuations in shell accumulation in the sediment record to represent changes in the balance between precipitation and evaporation during the ‘Little Ice Age’ (LIA; ~1400–1850 CE) and Industrial (1850–present) periods. Comparisons between indices of reconstructed ENSO and AMO variability, the abundance of the freshwater gastropod Pyrgophorus parvulus and the 18O records from ostracod calcite suggest that the relative influence of ENSO and AMO on long-term rainfall patterns in Barbuda has changed over the last 400 years. Our findings are in agreement with other high-resolution palaeoclimate studies that suggest that long-term changes in effective precipitation during the LIA were much more variable, temporally and spatially, than previously suggested.
Stand-replacing wildfires are a keystone disturbance in the boreal forest, and they are becoming more common as the climate warms. Paleo-fire archives from the wildland–urban interface can quantify the prehistoric fire regime and assess how both human land-use and climate change impact ecosystem dynamics. Here, we use a combination of a sedimentary charcoal record preserved in varved lake sediments (annually layered) and fire scars in living trees to document changes in local fire return intervals (FRIs) and regional fire activity over the last 500 years. Ace Lake is within the boreal forest, located near the town of Fairbanks in interior Alaska, which was settled by gold miners in AD 1902. In the 400 years before settlement, fires occurred near the lake on average every 58 years. After settlement, fires became much more frequent (average every 18 years), and background charcoal flux rates rose to four times their preindustrial levels, indicating a region-wide increase in burning. Despite this surge in burning, the preindustrial boreal forest ecosystem and permafrost in the watershed have remained intact. Although fire suppression has reduced charcoal influx since the 1950s, an aging fuel load experiencing increasingly warm summers may pose management problems for this and other boreal sites that have similar land-use and fire histories. The large human-caused fire events that we identify can be used to test how increasingly common megafires may alter ecosystem dynamics in the future.
Hilly regions along the Western Carpathian–Pannonian border are phytogeographically important, but their vegetation history remains largely unknown. We analysed two peat cores of Late Glacial origin from a bog woodland in the Malé Karpaty Mts (SW Slovakia) using plant macrofossil, pollen, peat chemistry and charcoal analyses to trace local successional patterns, regional vegetation development and occurrence of rare species. The small distance between the two profiles situated within homogeneous vegetation enabled us to explore small-scale differences in local vegetation history. The sediment started to accumulate at the end of the Allerød (ca. 12950 cal. yr BP), when a shallow oligotrophic/mesotrophic lake with macrophytes developed. Open pine-birch forests dominated in the landscape. During the early Holocene, the lake was infilled, mire vegetation appeared and broad-leaved forests spread in the surroundings. Two fire events indicated by increases in number of macroscopic charcoal particles were recorded. The first one, which occurred at the end of the Late Glacial, was found only in one of the profiles, while the second one affected entire mire and probably caused a hiatus spanning the middle and late Holocene. Fagus started to spread no later than 5800 cal. yr BP. Open mire vegetation reappeared after the fire (ca. 400 cal. yr BP). During the 19th century, the mire was overgrown by a birch bog woodland. The two profiles showed basically the same successional patterns, but some local events and occurrences of rare species (Potamogeton alpinus, Potamogeton praelongus, Scorpidium scorpioides and Pleurospermum austriacum) were traced only in one of them.
The Uddelermeer is a unique lake for The Netherlands, containing a sediment record that continuously registered environmental and climatic change from the late Pleistocene on to the present. A 15.6-m-long sediment record was retrieved from the deepest part of the sedimentary basin and an age–depth model was developed using radiocarbon dating, 210Pb dating, and Bayesian modeling. Lake-level change was reconstructed using a novel combination of high-resolution palaeoecological proxies (e.g. pollen, non-pollen palynomorphs, chironomids), quantitative determinations of lake-level change (ground-penetrating radar), and estimates of changes in precipitation (lipid biomarker stable isotopes). We conclude that lake levels were at least as high as present-day water levels from the late glacial to 3150 cal. yr BP, with the exception of at least one lake-level lowstand during the Preboreal period. Lake levels were ca. 2.5 m lower than at present between 3150 and 2800 cal. yr BP, which might have been the result of a change in moisture source region prior to the so-called 2.8-kyr event. Increasing precipitation amounts around 2800 cal. yr BP resulted in a lake-level rise of about 3.5–4 m to levels that were 1–1.5 m higher than at present, in line with increased precipitation levels as inferred for the 2.8-kyr event from nearby raised bog areas as well as with reconstructions of higher lake levels in the French Alps, all of which have been previously attributed to a phase of decreased solar activity. Lake levels decreased to their present level only during recent times, although the exact timing of the drop in lake levels is unclear.
The pattern of ancient sediment accumulation in lake basins is usually determined for the sole purpose of obtaining a chronology of the sequence. We develop graphical representations of lake basins and how they fill with sediment in order to make generalisations about sediment patterns which can be used to distinguish those that relate to an aspect of changing environment from those that relate solely to the shape of the basin itself. Our goal is general observations that could lead to more robust interpretation of age–depth models from lake basin sediments. We show that in nearly all circumstances with constant sedimentation, the overall pattern seen at a central core should be one of decreasing rate of sediment accumulation, which tends to be constant towards the top. In most situations, the initial rate of sediment accumulation is particularly high because of the basin shape. Observed rates of sediment accumulation that increase up the core should normally indicate increasing sediment input (either autochthonous or allochthonous). On the other hand, detailed information on basin shape is needed to break decreasing rates of sediment accumulation into components because of basin shape and decreasing sediment input. These considerations show that the pattern of sediment accumulation in a lake basin has intrinsic value as an indicator of environmental change and potential utility in chronology construction, but only when interpreted in the context of basin shape.
Biological conservation depends on understanding and disentangling the effects of decadal- to centennial-scale dynamics from the millennial-scale dynamics documented in the fossil record. The American Southwest is expected to become increasingly arid over the next few decades and will continue to experience large-scale human land use in various forms. A primary question is whether the ecological fluctuations recorded over the past few decades fall outside the range of variation expected in the absence of recent land use and management. I excavated and quantified mammal diversity change in two fossil-bearing alcoves, East Canyon Rims 2 and Rone Bailey Alcove, located in San Juan County, Utah. AMS radiocarbon dates on 33 bone samples from these sites span ~4.4–0.5 kyr and shed light on pre-industrial faunal dynamics in the region over the course of environmental change. Localities with comparable small mammal diversity have not been reported from this region previously, so these deposits provide novel insight into Holocene mammal diversity in southeastern Utah. Taxa recorded in these sites include leporids, sciurids, perognathines, arvicolines, Onychomys, Cynomys, Dipodomys, Peromyscus, Neotoma, and Thomomys. Using temporal cross-correlation, I tested for a relationship between regional temperature and species richness, evenness, relative abundance, and rank abundance. I also tested for changes in the overall taxon abundance distribution and visualized faunal relationships among time bins using non-metric multidimensional scaling of relative abundance data. None of the measures of diversity tested here were correlated with temperature change through time except for relative abundance of leporids. Overall, these results suggest that climatic fluctuations of the magnitude preserved in these deposits did not significantly alter the small mammal community, nor is there evidence that the presence, then exodus, of Native Americans from the region significantly affected small mammals.
The number of debris-covered glaciers featuring supraglacial trees is increasing worldwide as a response of high mountain environments to climate warming. Generally, their distribution on the glacier surface is not homogeneous, thus suggesting that some glacier parameters influence germination and growth of trees. In this study, we focused our attention on the widest Italian debris-covered glacier, the Miage Glacier (Mont Blanc massif). We analyzed the ablation area in the range from 1730 to 2400 m a.s.l. where continuous debris coverage is present and trees are found. Using data obtained by remote sensing investigations and field surveys, we defined a record of glacier parameters to be analyzed with respect to the presence and abundance of trees. We found that supraglacial trees are present at the Miage Glacier (1) whenever exceeding a debris thickness threshold (>=19 cm), (2) with a gentle slope (<=10°), (3) with a low glacier surface velocity (<=7.0 m/yr), and (4) where the vertical changes due to glacier dynamics are positive (i.e. prevalent increase ranging between +7 and +28 m over 28 years due to both slow debris accumulation and preservation of ice flow inputs). The statistical analysis supports our findings. The analysis of the same parameters might be conducted on other debris-covered glaciers featuring supraglacial trees, in order to evaluate whether such conditions are local ones or whether they are general factors driving germination and growth of trees. By identifying the features supporting the presence and growth of trees in these environments, and their thresholds, a contribution is given for a better understanding of the importance of debris-covered glaciers and, in general, of debris-covered ice, as a refuge for trees during glacial and warm intervals of the Holocene.
Aeolian sand sheets and active dunefields preserve an ancient Holocene land surface represented by palaeosols that occur around the present ice margin in the Kangerlussuaq area, West Greenland. To determine the relation between Holocene aeolian activities and periods of soil formation, both substantially dependent on the deglaciation history, palaeosols, aeolian sand sheets and dunefields were analysed using field data, grain size analyses, optically stimulated luminescence dating and AMS 14C data in an area of about 15 km2 of the Umimmalissuaq valley. Palaeosols are developed close to the ice margin (<2 km) in fine-grained aeolian sediment (silt loam) and covered by sandy aeolian layers. Silt contents of palaeosols (partly >60 wt%) are comparable with aeolian sand sheets currently formed at greater distances (4–5 km) from the present ice margin. We propose a transport distance for fine aeolian sediments, in which the palaeosols are formed, of at least 4 km from inboard of the present ice margin. Soil formation of the palaeosols started around 2700 cal. yr b2k. Ages from the youngest parts of the palaeosols suggest a stable period of around 2400 years, allowing for pedogenesis. This period was characterised by low but constant aeolian activity. Since aeolian activity intensified after around 300 cal. yr b2k and is still resulting in active dunefields with coarse and medium sand accumulation, the ice margin must have reached its present position at that time.
Large-scale atmospheric pressure centers, such as the Aleutian and Icelandic Low, have a demonstrated relationship with physical lake characteristics in contemporary monitoring studies, but the responses to these phenomena are rarely observed in lake records. We observe coherent changes in the stratification patterns of three deep (>30 m) lakes inferred from fossil diatom assemblages as a response to shifts in the location and intensity of the Aleutian Low and compare these changes with similar long-term changes observed in the 18O record from the Yukon. Specifically, these records indicate that between 3.2 and 1.4 ka, the Aleutian Low shifted westward, resulting in an increased frequency of storm tracks across the Pacific Northwest during winter and spring. This change in atmospheric circulation ultimately produced deeper mixing in the upper waters of these three lake systems. Enhanced stratification between 4.5 and 3.3 ka and from 1.3 ka to present suggests a strengthened Aleutian Low and more meridional circulation.
We examine the ability of four different regression-tree ensemble techniques (bagging, random forest, rotation forest and boosted tree) in calibration of aquatic microfossil proxies. The methods are tested with six chironomid and diatom datasets, using a variety of cross-validation schemes. We find random forest, rotation forest and the boosted tree to have a similar performance, while bagging performs less well and in several cases has trouble producing continuous predictions. In comparison with commonly used parametric transfer-function approaches (PLS, WA, WA-PLS), we find that in some cases tree-ensemble methods outperform the best-performing transfer-function technique, especially with large datasets characterized by complex taxon responses and abundant noise. However, parametric transfer functions remain competitive with datasets characterized by low number of samples or linear taxon responses. We present an implementation of the rotation forest algorithm in R.
Sea-level rise (SLR) is one of the most conspicuous examples of the environmental impact of recent climate change. Since SLR rates are not uniform around the planet, local and regional data are needed for proper adaptation plans. 210Pb-dated sediment cores were analyzed to determine the trends of sediment accretion rates (SARs) at three tropical saltmarshes in the Estero de Urias lagoon (Gulf of California, Mexico), in order to estimate the SLR trends during the past ~100 years, under the assumption that these ecosystems accrete at a similar rate to SLR. A chemometric approach, including multivariate statistical analysis (factor analysis) of geochemical data (including 13C; 15N; C/N ratios; and Br, Na, and Cl as proxies for marine transgression) was used to identify the marine transgression in the sediment records. Based on core geochemistry, only one of the three cores provided a long-term record attributable to marine transgression. SLR trends, estimated from SARs, showed increasing values, from a minimum of 0.73 ± 0.03 mm yr–1 at the beginning of the 20th century and up to 3.87 ± 0.12 mm yr–1 during the period 1990–2012. The estimated SLR trend between 1950 and 1970 was comparable to the tide gauge records in Mazatlan City for the same period. Results showed the caveats and strengths of this methodology to reconstruct decadal SLR trends from the sedimentary record, which can be used to estimate long-term SLR trends worldwide in regions where monitoring data are scarce or absent.
The Gran Sabana (GS) is a key region for understanding the origin of neotropical savannas and is an ideal location to test ecological hypotheses on long-term vegetation dynamics under the action of natural and anthropogenic drivers. The conservation of the GS is a controversial issue because of the confluence of disparate cultural and socio-economic interests, with a strong debate surrounding fire practices by indigenous people. Late glacial to Holocene pollen and charcoal records obtained thus far in this region have documented the main palaeoecological trends along with the climatic and anthropogenic (mostly fire) drivers involved. Here, we discuss how these records can be used to inform conservation and restoration practices in the GS. The main points of the discussion are the local versus regional character of palaeoecological evidence, the support provided by this evidence for the existing fire management proposals and the role of spatiotemporal environmental and ecological heterogeneity in the definition and evaluation of realistic restoration targets. A general conclusion is that past ecological reconstructions do not fully support either of the current options for fire management, that is, either total fire suppression or the continuity of indigenous fire practices. It is recommended to replace this dual and rigid conservation framework with a more diverse and flexible approach that considers the complex spatiotemporal heterogeneity documented in palaeoecological records.
We have measured pollen, aluminum, and lead abundances in a Czech peat bog at Bozi Dar in order to investigate the environmental impact of Holocene climate changes and mining activities in Central Europe. The pollen record shows a continuous vegetal cover since 13 kyr BP. Aluminum and pollen deposition characterize the Younger Dryas (YD) cold event at 12.3–11.0 kyr BP, within its expected time frame in Northern Europe. Aluminum fluxes reveal four other significant dust events with significant Asian and Saharan sources, as shown with variations in stable 204Pb, 206Pb, and 207Pb isotopes. Recurrent Asian incursions are seen at Bozi Dar during the YD and Mid-Holocene dust events (at 7.1, 6.5, and 5.9 kyr BP). These Asian imprints are also observed by Le Roux and colleagues during the YD in the nearest Holocene-long geochemical peat record from Switzerland (Etang de la Gruère). We do not see at Bozi Dar the distinct western European volcanic inputs identified in the Swiss peat by Shotyk and colleagues. However, isotopic ratios characteristics of Mediterranean airflows are evident at both locations during the Mid- and Late Holocene. The occurrence of these various air mass sources in Switzerland and the Czech Republic substantiates Holocene atmospheric circulation models in Central Europe with dominating zonal airflows during the Early Holocene, followed by a governing meridian dispersion during the Mid- and Late Holocene. Lead inputs at 5.1–4.3 and 1.9 kyr BP cannot be explained by increased dust deposition only. The 1.9 kyr event fits local Bohemian ore isotopic imprints of which isotopic signatures are seen as early as 2.2 kyr BP in our core, hence revealing the oldest ever environmental record of mining-related activities in the Czech Republic. Relatively elevated Pb deposition at 5.1 and 4.3 kyr BP are tentatively attributed to contamination that may be from local sources and/or long-range transport.
Siberian lime (Tilia sibirica) is a broad-leaved deciduous tree closely related to European Tilia cordata. It is endemic to a few sites in southern Siberia, located approximately 2000 km east of the limit of the European deciduous forest biome. These isolated sites with locally increased precipitation can be considered as potential analogues of the glacial refugia of temperate trees. To understand the ecology of such refugia, we studied the history and recent dynamics of the forests containing T. sibirica using soil charcoal and tree-ring analyses at the largest locality of this species (Kuzedeevo). These forests are currently dominated by Populus tremula and Betula pendula, with scattered occurrence of Abies sibirica and Tilia, which form small monodominant stands locally. Soil charcoal indicated continuous occurrence of all of these trees more than 1000 years ago, but the dominant species in the past were Abies and Populus. Current patches of Tilia-dominated forests are even-aged, 40–80 years old, with tree-ring patterns indicating their origin in open areas, probably after logging in the 20th century. After disturbance, Abies seedlings tend to be outcompeted by tall herbs, whereas Tilia can form small monodominant stands through vegetative regeneration. However, in the natural undisturbed Abies–Populus forest, Tilia was probably a subordinate species. Analogously to this modern Siberian ecosystem, temperate deciduous trees, especially those with vegetative regeneration, may have survived as rare components of coniferous forests in glacial periods at locally favorable sites such as those with increased orographic precipitation and protection by a thick snow cover.
This research was conducted in the Northern Apennines, in the upper valleys of the Cedra River and Parma River, occupied by glaciers during the last glacial maximum. The stratigraphy, the dating and the interpretation of the environmental significance of alluvial deposits interbedded between lacustrine sediments are reported. The data provide an overview of the periods of enhanced alluvial activity that occurred after the glacial retreat in the Apennine chain. The alluvial phases and the periods of environmental stability varied in frequency and length during the Holocene. In particular, starting from the beginning of the Apennine Neoglacial (about 4.2 kyr BP), the events became much more frequent but shorter. The elapsed time between alluvial phases (i.e. the length of the phases of stability) was greater during the Early Holocene, probably because of the values of insolation: when the insolation in July was lower, the length of the phases of stability was greater. Despite the uncertainty in the dating of some events, it is likely that many alluvial phases, later than about 8.5 kyr BP, started during ice rafted debris events in the North Atlantic. The overall analysis of the alluvial sedimentation indicates that periods of more frequent floods are associated with times of rapid climate change and not only with cool periods. The current increase in floods, linked to the ongoing climate change, confirms the data obtained from Holocene sediments.
Macroscopic charcoal records can be used to infer spatially explicit reconstructions of past fire history. However, a current deficiency in the charcoal-analysis toolbox has been the lack of a method to consider sampling variability and charcoal-particle area distributions for peak detection with charcoal-area records. We present a screening procedure specific for datasets comprising charcoal numbers and areas to screen the charcoal-area estimates with respect to the count sums. The rationale for screening charcoal-area peaks stems from the observation that although charcoal-area records can be more suitable in a statistical sense for peak detection (e.g. as established by the signal-to-noise index), charcoal-area peaks can be questionable if they are determined by just one or a few larger charcoal particles. Our method begins with a charcoal-area time series analysed by existing methods to identify peaks representing fire episodes. To screen these peaks, the method uses bootstrap resampling of charcoal-particle areas observed in a user-defined subsection of the record around each peak to obtain the range of likely charcoal areas for different counts. Peaks with total area within the likely range of bootstrapped samples (e.g. p > 0.05) are flagged as potentially unreliable, whereas samples with total area significantly greater than expected by chance are deemed robust indicators of past fire events. In an example application of the method to a charcoal record from Lake Brazi, Romania, several peaks failed to pass the screening suggesting that, as for count-based records, unscreened charcoal-area records may include spurious fire episodes and thus potentially underestimate past fire-return intervals.
Despite the multiple constraints of using shell mounds for building relative-sea-level (RSL) curves, one of the premises behind this use is still valid in modern archaeological research. This refers to the sites being continuously built near bodies of water rich in fish species and mollusk beds. Studies that combine the evolution of settlement patterns with the geological evolution of coastal areas in Brazil reach analogous results: the distribution of shell mounds in time and space follows the landscape transformations induced by RSL variations through the Holocene. Although shell mounds are not precise indicators of RSL, they provide evidences of the paleo-geographical changes during the Holocene, of which RSL is one of the many control variables. By collecting and transporting mollusks to the shell mounds, humans inevitably carry sediments from the substrate where mollusks live, for example, the beaches and lagoons near the sites. In this work, the geoarchaeological study of three shell mounds located in the southern coast of Santa Catarina State, combined with mollusk taxa identification, show the direct association of shell mound content with the changing landscape. The predominance of Ostrea sp. versus Anomalocardia brasiliana, the presence of colluvial versus lagoonal sediments, and the occurrence of echinoid spines versus muddy aggregates with diatoms, gastropods, and glauconitic clay characterize the distinction between sites built before and after the maximum Holocene transgression, respectively. This attests the potential of geoarchaeological analyses in shell mounds as a complementary proxy for paleo-environmental reconstructions.
This study examines geological evidence for earthquakes and tsunamis based on data obtained from 14 sediments cores and one trench in the coastal area of the Shimizu Plain, Japan. The Shimizu Plain is located onshore of the Suruga Trough, which marks the convergent boundary between the Eurasian and Philippine Sea plates. On the basis of lithologies, fossil contents, and radiocarbon dating, we identified geological and paleontological evidence for abrupt changes in depositional environments related to coseismic uplift associated with the
Uninterrupted, annually resolved paleoclimate records are crucial to contextualize the current global change. Such information is particularly relevant for the Europe realm for which weather and climate projections are still very challenging if not virtually impossible. This study presents the first precisely dated, annually resolved, multiregional Arctica islandica chronologies from the North Sea which cover the time interval
Although the Pamir Plateau is an ideal place to investigate paleo-environmental changes in the westerlies-dominated high Central Asia, there are only few Holocene records from this region. We present a sub-centennially resolved lacustrine record of moisture variations from Sasikul Lake, central Pamir Plateau, based on geochemical, sedimentological, and mineralogical proxies. Our results show that generally dry conditions at Sasikul Lake during the past 2540 years were interrupted by a pronounced wet period between
Stomatal density of plants may vary depending on environmental factors, such as CO2 concentration. Under the current atmospheric conditions, it is expected that leaves have different stomatal density than they had hundreds or thousands of years ago, due to the rise in CO2 in the atmosphere. Coprolites of the extinct Myotragus balearicus from Cova Estreta (Pollença, Mallorca), with a radiocarbon age of 3775–3640 cal.
This paper investigates the interaction between groundwater and groundwater-dominated Crescent Spring in an aeolian sand environment to determine the drainage source of groundwater for the lake using hydraulic gradient and isotope analysis methods. The precipitation is found to have an insignificant effect on the lake in an arid climate environment. Hydrogen and oxygen isotopic evidence presents at least two aquifer contributions that recharge 87% and 13% water supply of the lake, respectively. The flow direction of groundwater is theoretically established based on the hydraulic gradient and isotope analysis methods.
Utah’s Great Salt Lake (GSL) is a closed-basin remnant of the larger Pleistocene-age Lake Bonneville. The modern instrumental record of the GSL-level (i.e. elevation) change is strongly modulated by Pacific Ocean coupled ocean/atmospheric oscillations at low frequency, and therefore reflects the decadal-scale wet/dry cycles that characterize the region. A within-basin network of seven tree-ring chronologies was developed to reconstruct the GSL water year (September–August) level, based upon the instrumental record of GSL level from 1876 to 2005. The result was a 576-year reconstruction of the GSL level that extends from 1429 to 2005; all calibration-verification tests commonly used in dendroclimatology were passed. The reconstruction explains 48% of the variance in the instrumental GSL level and exhibits significant periodicity at sub-decadal scales over the past six centuries. Meanwhile, predominance of multi-decadal periodicity in the early half of the record shifted to quasi-decadal dominance in the latter half, and this is consistent with that of proxy reconstructions of the Pacific Decadal Oscillation. The GSL-level reconstruction is a crucial component to improving our insight into the possible controls of coupled ocean-atmosphere interactions on precipitation delivery.
Continuous sediment, charcoal, and pollen records were developed from a ~7-m sediment core from Prater Canyon in Mesa Verde National Park (MEVE), Colorado, USA. Sediment input into the canyon is episodic and is linked to precipitation runoff and vegetation cover. Pollen recovered from the Prater Canyon sediment core reflect the vegetation changes within the MEVE region. During the period recorded, the vegetation of the region surrounding Prater Canyon transitioned from xeric adapted species in an open environment to a more mesic, Pinus edulis–Juniperus osteosperma (piñon–juniper) woodland over the last 1500 years. Two distinct changes in fire frequency occurred. Before 4080 cal. yr BP, fires occurred at a much more frequent rate (2.5–12 fires/200 years) than from 4060 cal. yr BP to present (0–2 fires/200 years). Most importantly, the variations occurring in the charcoal record for the past 2500 years coincide with both shifts in human occupation and climate fluctuations within the region, with burning increasing during Ancestral Puebloan occupation and moist but increasingly dry conditions, and declines in both at the end of the ‘Medieval Climate Anomaly’ (MCA). The record from Prater Canyon demonstrates the importance of the Ancestral Puebloans in landscape modification during their occupation from
High-temporal resolution analysis of different climatic tracers (pollen, foraminiferal-based winter sea surface temperature (SST), benthic foraminiferal 18O) from marine core MD95-2042, retrieved off SW Iberia, allows us to directly compare, without any chronological ambiguity, Mediterranean vegetation and eastern North Atlantic winter SST changes for the last 14.2 kyr. We identify on land and in the ocean several climatic phases such as the end of the warm and humid Bølling–Allerød, the cold and dry Younger Dryas, and the warm and humid Holocene with the Mediterranean forest (MF) optimum between 9.6 and 8.1 kyr. This record shows that, at multi-centennial timescale (~800 years), declines in forest cover generally related to dry and cool periods in southern Iberia are synchronous with cold SST in the eastern part of the North Atlantic subtropical gyre. At multi-centennial timescale, changes in thermohaline circulation, via freshwater content fluctuations, appear to be responsible for the coupling between dryness in Iberia and SST cooling in eastern North Atlantic subtropical gyre. In contrast, some Holocene events include centennial-scale oscillations (~100 years) marked by MF declines in southern Iberia concomitant with SST warming in the eastern North Atlantic subtropical gyre. This climatic pattern is similar to that observed at decadal timescale under the influence of the positive mode of the North Atlantic Oscillation (NAO). We suggest, therefore, that synchronous SW Iberian dryness and SST warming at centennial timescale could be explained by atmospheric fluctuations related to NAO changes.
Past vegetation assemblages, preserved in peat layers, are one of the key proxies when reconstructing historical peatland dynamics. Northern peatlands can be divided into two main types: fens and bogs. Compared with bog peat, the fen peat is usually more decomposed because of different eco-hydrological conditions and effective humification processes. A high level of decomposition hampers reliable identification of plant remains and constrains palaeoecological approaches. Biogeochemical studies on bog plants and bog peat have shown that plant group–specific biomarkers can be applied to identify fossil plants or plant groups from peat, given the identification of plant group–specific markers in living fen plants. In this study, we applied plant macrofossil, biomarkers and multivariate statistical analyses to two mid-boreal peat sequences to investigate whether biomarkers can be applied to distinguish fen and bog environments and whether plant-specific biomarkers can be identified from fen peat. Macrofossil analyses clearly separate dry bog hummocks, moist lawns and wet fen habitats apart. Corresponding division emerged when the biomarker data were combined with the macrofossil data. Moreover, we succeeded to separate bog and fen habitats apart by the changes in n-alkane and the n-alkane ratio distributions along the cores. The fen–bog transition zone was indicated by high sterol and triterpenoid concentrations and changes in degradation measures. However, it remains a challenging task to attain species-level information of past plant assemblages from highly humified fen peat layers based on biomarkers only.
A two-dimensional shallow ice-flow model, yielding the glacier geometry at selected time intervals, is used to simulate the development of Spørteggbreen (1) from 8000 cal. yr BP to the present, (2) from
Researchers have established a Holocene pattern of Bison spp. diminution on the Great Plains of North America. This pattern, however, is less clear west of the Rocky Mountains. This lack of clarity stems from a relative paucity of paleontological and archaeological bison assemblages sufficiently large enough to understand local bison diminution. To begin filling this important gap in knowledge, we analyze a large bison assemblage from Baker Cave, a Late-Holocene archaeological site located on Idaho’s Snake River Plain. Measurements of humeri, radii, tibiae, metatarsals, and calcanei demonstrate that these animals were significantly smaller than Early-Holocene bison from both the Great Plains and Snake River Plain. Middle-Holocene bison from the Great Plains are generally larger than those from Baker Cave, but this size difference varies by skeletal element. The Baker Cave bison do fall within the range of Late-Holocene morphological variation present in both Snake River Plain and Great Plains bison populations. These results provide a necessary first step for understanding bison morphology in the region, but establishing a pattern of diminution west of the Rocky Mountains will require follow-up studies with other faunas.
Forest and peatland ecosystems constitute the two major carbon pools in the boreal region. We assess the evolution in total storage and partitioning of ecosystem carbon following recent paludification of forest into peatland at two sites in Northeast European Russia. Based on radiocarbon dating of basal peat and quantification of total ecosystem carbon storage, our results show that paludification rates and its consequences for carbon storage vary significantly between sites. A peatland expanding on ground with steeper slopes has experienced a slow lateral advance in recent times, about 2.6 m on average per century, whereas a peatland in flatter terrain has expanded much more rapidly, about 35 m on average per century. The total ecosystem carbon storage (sum of phytomass, top soil organics or peat, and 30 cm of underlying mineral soil) showed a long-term trend toward increased ecosystem C storage following the replacement of forest (mean value = 20.8 kg C/m2, range = 13.0–43.4 kg C/m2) by peatland (>100 kg C/m2 in the deepest peat deposits). However, the transitional stage in which the forest is replaced by the margin of the peatland results in a short-term decrease of carbon stored in the ecosystem with a mean loss of 7.5 kg C/m2. After the initiation of a peatland through paludification, a period of decades to centuries of peat accumulation is needed to compensate for the initial loss of carbon. In the short term, an intensification of the paludification process could lead to a loss of carbon stored in the boreal region.
Climate, land use and fire are strong determinants of plant diversity, potentially resulting in local extinctions, including rare endemic and economically valuable species. While climate and land use are decisive for vegetation composition and thus the species pool, fire disturbance can lead to landscape fragmentation, affecting the provisioning of important ecosystem services such as timber and raw natural resources. We use multi-proxy palaeoecological data with high taxonomic and temporal resolution across an environmental gradient to assess the long-term impact of major climate shifts, land use and fire disturbance on past vegetation openness and plant diversity (evenness and richness). Evenness of taxa is inferred by calculating the probability of interspecific encounter (PIE) of pollen and spores and species richness by palynological richness (PRI). To account for evenness distortions of PRI, we developed a new palaeodiversity measure, which is evenness-detrended palynological richness (DE-PRI). Reconstructed species richness increases from north to south regardless of time, mirroring the biodiversity increase across the gradient from temperate deciduous to subtropical evergreen vegetation. Climatic changes after the end of the last ice age contributed to biodiversity dynamics, usually by promoting species richness and evenness in response to warming. The data reveal that the promotion of diverse open-land ecosystems increased when human disturbance became determinant, while forests became less diverse. Our results imply that the today’s biodiversity has been shaped by anthropogenic forcing over the millennia. Future management strategies aiming at a successful conservation of biodiversity should therefore consider the millennia-lasting role of anthropogenic fire and human activities.
Holocene vegetation records are presented from palaeochannels in the southern Kelabit Highlands, at Pa’Dalih (PDH 212) and at Pa’Buda (BPG), and from a peat bog in the northern Kelabit Highlands, at Bario (Ba). Results are based on changes in the sediment lithology, loss-on-ignition, magnetic susceptibility, pollen, phytoliths and other palynomorphs. At Pa’Buda, possible clearance occurred ~6500 cal. BP, perhaps for arboriculture. More pronounced signatures of clearance are at PDH 212 by ~3100 cal. BP, and at Ba by 1300 cal. BP. Propagation/cultivation of the sago palm, Eugeissona, may have been taking place by ~2800 cal. BP at site PDH 212 and was probably taking place by at least 1300 cal. BP at Ba. Rice cultivation may have been taking place between 2800 and 1200 cal. BP at PDH 212, but this remains speculative, due to the morphological features of the Oryza bulliforms, but it was likely taking place at Pa’Dalih by 530–490 cal. BP, where Oryza bulliforms, with characteristics similar to domesticated types are present, and there was a sharp rise in sedimentation, caused by intense burning. At Ba, within the last 600 years, an increase in Palmae phytoliths may signify increasingly intense human impact. In more recent times, both rice and banana cultivation are represented in the phytolith record at Pa’Buda.
Within the framework of a regional research project on wetlands as cultural heritage sites, an attempt was made to examine the natural and anthropogenic causes driving the vegetation dynamics and exploitation of a small mountain wetland. To assess its potential use as an archive of the landscape history, an environmental archaeology approach was used: palaeoenvironmental data from traditional pollen sampling by coring were matched with stratigraphic information from an excavation area of several square metres, and plant micro- and macroremain analyses (e.g. pollen assemblages, micro- and macrocharcoal, morphological and dendrochronological features of waterlogged tree trunks) were compared in order to evaluate them as effects of different environmental factors and to pinpoint these factors. In this paper, the focus is set mainly on the results originating from pollen analyses of a core drilled in the peat-bog, a few metres from the stratigraphic excavation. The start of peat deposition, sometimes coinciding with human activity, was dated around 10,000 cal. BP. The impact on the vegetation surrounding the site is clearly recorded in the pollen assemblages only from the Roman period (2010–1820 cal. BP) even though a long history of human presence is archaeologically documented in the area since the Palaeolithic. Since that time, the abrupt decline of fir favoured the final spread of beech which, in turn, in the Middle Ages (1180–790 cal. BP) leaves space to grassland exploitable for pasture and for agro-silvi-pastoral activities. This site has proven to be of great importance for the Holocene history of the silver fir.
Quantitative palaeoclimatic reconstructions based on biological fossils are a major source of information on long-term climatic variability. Such reconstructions typically use some kind of a modern calibration data set describing the variation of the studied biological group in present-day climate space. Here, we explore the effect of calibration data set selection on palaeoclimatic reconstructions, by creating alternate calibration data sets via stratified random sampling to reconstruct mean July temperature (Tjul) for four fossil pollen sequences from northern Europe. We show that palaeoclimatic reconstructions using methods based on taxon-response models can be highly sensitive to the calibration data set used. In particular, the absolute reconstructed temperatures show great sensitivity to calibration data selection, which suggests that the absolute values of palaeoclimatic reconstructions may not be robust. By contrast, we find the relative shapes of the reconstructed curves to be more robust to calibration data selection because taxa tend to occupy similar relative locations along the sampled gradient regardless of calibration data set location. Based on this robustness of relative palaeoclimate curves, we suggest a debiasing procedure in which palaeoclimate values are estimated by fixing the relative curve with the modern observed value, thus correcting biases resulting from calibration data selection.
Transfer of nutrients from terrestrial to aquatic ecosystems is a natural process with climatic, biotic, and geologic controls. Recently, increasing concern about human manipulation of global nutrient cycles has required a long-term approach to assessing the nutrient status of aquatic systems. Data available in palaeorecords can assess current trophic status, baseline conditions, and long-term processes controlling nutrient fluxes on decadal to millennial timescales. Here, we review three palaeolimnological methods used to reconstruct nutrient cycling: (1) chemical compounds preserved in lacustrine sediment, (2) aquatic biotic indicators (often using a quantitative transfer function), and (3) quantitative empirical sediment flux estimates. The millennial-scale regulation of nutrient cycling by climate and catchment geochemistry leads to a gradual trajectory of dystrophication over the Holocene in many temperate lakes. In many systems, the magnitude of recent anthropogenic changes to nutrient cycling is large compared with natural fluctuations, but this perspective could also be due to the selection of study sites that are currently experiencing eutrophication. Increased nutrient loading to aquatic systems is not always accompanied by decreased ecosystem function. The powerful temporal perspective from palaeolimnology can be complemented with modern mechanistic approaches to lead to increased understanding of the rates, patterns, and mechanisms of nutrient fluxes.
There has been an increasing need to reconstruct past climate from proxy records quantitatively and mechanistically. The inverse proxy modeling method stands out as a novel approach to quantitative palaeoclimate reconstructions through integrating process-based models and proxy records, representing a major progress in quantitative palaeoclimatology. It has been proposed to incorporate multiple proxy records to produce a more robust constraint on the climate parameters sought for estimation, and most of the work has been conducted using pollen records in conjunction with vegetation models. Here, I show a worked example of using paired stable oxygen and carbon isotope records of peat cellulose from one single core to infer the climate history in NE China for the last 6000 years through solving a well-posed inverse problem using Bayesian statistics. The quantitative palaeoclimate data obtained in this study may deepen our insight into the dynamics of the East Asian summer monsoon. Mean growing season temperature and relative humidity show millennial-scale fluctuations prior to c. 4000 cal. yr BP; thereafter, centennial-scale fluctuations prevailed, revealing the relative importance of solar activity over tropical ocean–atmosphere interactions in regulating the variability of regional climate during the late Holocene. It appears that there was a prominent out-of-phase relationship between temperature and relative humidity, due probably to the different response of these climate elements to orbital forcing and land cover. This worked example demonstrates the potential of using model–data fusion techniques to produce physically meaningful, mathematically optimal, and geologically sound results.
Human access to natural resources (or provisioning ecosystem services) is controlled by climate conditions and usage. In the central Andean highlands, around Lake Titicaca, water and woodlands have been critical resources for human populations over the last 5000 years. During this time period, human society developed from mobile hunter–forager groups into settled agrarian populations (c. 3400 years ago) through to the rise of some of the first ‘civilizations’ in the central Andes (c. 2500 years ago). Records of past environmental and vegetation change reveal that coincident with these societal reorganizations were variations in the availability of water and woodland resource. Prior to Hispanic arrival in the central Andes (before AD 1532), changes in availability of natural resources are shown to be concomitant with societal reorganizations; however, changes in societal organization are shown not to necessarily result in the degradation of ecosystem services (i.e. woodland resource available). Through the last 5000 years, three concomitant repeated adaptive cycles of destabilization, reorganization, growth and maxima are identified in human and ecological systems. This suggests that long-term (>100 year) societal development was paced by both increases and decreases in ecosystem service provision. The approach of past societies to dealing with changes in baseline resource availability may provide a useful model for policymakers to consider in the light of the predicted scarcity of resource over the coming decades.
Using various archaeological and geoarchaeological operations, charcoal and waterlogged wood assemblages have been sampled in the marshy areas from the lower Dauphiné (Rhone valley, France). Their identification allows reconstructing the evolution of the woody vegetation in relation to climatohydrological changes and with human practices in the plain since the mid Holocene. It appears that humid-land forests have experienced a shift from ash formations (dominating during Pre- and Protohistory) toward alder formations between the Bronze Age and Roman Period. That vegetation change seems to be linked with pastoral practices in which fire is used as a clearing and regeneration tool. The intense pastoral use of the plain, together with the humidity of the soils when not artificially drained, may also have prevented the development of dense and mature forests. Finally, we show that beech, which is currently absent from the plain, probably grew in the marshlands during the past.
Holocene paleoclimate records from Greenland help us understand the response of the Greenland Ice Sheet and regional oceanic and atmospheric circulation systems to natural climate variability in order to place recent changes in a longer-term perspective. Here biogeochemical analysis of a lake sediment core from southeast Greenland is used to define changes in moisture balance and runoff during the Holocene in a catchment near the margin of the Greenland Ice Sheet. A 1.6 m sediment core that spans the last 8.8 ka was recovered from Flower Valley Lake on Ammassalik Island. Magnetic susceptibility, diatoms, bulk biogeochemical properties (TOC, C/N, 13Corg), and lipid biomarkers (n-alkanes; C16–C31) reveal changes in clastic sedimentation and the relative input of terrestrial- and aquatic-derived organic matter. Hydrogen isotope values (D) of mid- (n-C25) and long-chain (n-C29, n-C31) n-alkanes allow reconstruction of D of precipitation and summertime evaporation of lake water. Following a period of early lake ontogeny and landscape stabilization after deglaciation from 8.4 to 7.0 ka, the mid Holocene, 8.4–4.1 ka, is characterized by greater evaporative enrichment of the lake water as indicated by D records. After 4.1 ka, there is a decrease in evaporative enrichment of the lake water. There is also an abrupt transition to more variable sedimentation marked by sharp increases in magnetic susceptibility, C/N, 13Corg, and the concentration of long-chain n-alkanes, showing periodic delivery of terrestrial organic matter and clastic sediment to the lake. Higher insolation during the mid Holocene resulted in a warmer and drier climate with longer ice-free periods in the summer and enhanced evaporation of lake water. The reduction in insolation and colder temperatures during the late Holocene caused a reduction in evaporation of lake water over the last 4.1 ka and was accompanied by periodic increases in surface runoff, which correspond with intervals of cold Greenland Ice Sheet surface temperatures.
High-resolution macroscopic charcoal and sediment analysis was used to reconstruct fire history and environmental changes from three loess-paleosol profiles on the semi-arid loess tableland landscape during the Lateglacial period and the Holocene. Analysis of charcoal concentrations, influx, and the ratios of particle-size classes (from which changes in charcoal taphonomy over time are inferred) in the profiles show spatially coherent patterns of change that relate to regional variations in climate. Effective moisture variability on century to millennial timescales and regional differences in fuel availability appear to be the most important controls on fire from the Lateglacial period to the mid Holocene (12,000–3100 yr BP). Conversely, asynchronous fire patterns during the late Holocene appear to indicate regional and temporal variations as well as changing intensities of human activity. Land use intensified in the region during the late Holocene, when the climate became more arid, and a distinct increase in charcoal concentration then indicated an unprecedented increase in biomass burning. The increase in fire activity occurs in the recent loess layer (L0) and the surface soil (TS) consistent with the establishment of irrigated farming for cereal cultivation in the southern part of the study region about 3100 yr BP. Broad-scale land reclamation was extended to the loess tableland region about 2170–1730 yr BP (during the Qin-Han Dynasty period), and the rapidly decreasing charcoal concentration in the accumulated topsoil (at depths of less than 20 cm) at the CCY site since 1500 yr BP is consistent with the development of terrace farming in the northern part of the study region at that time. In summary, the evolution of fire history in the study profiles across the region is closely related to (1) gradients in humidity; (2) spatial and temporal variability in the distribution and intensity of human land use; and (3) the buildup of burnable biomass, among which there was a nonlinear complex relationship during the Holocene. Increased efforts to synthesize and analyze multiple paleo-environmental records and to combine these with multiproxy evidence are needed to understand wildfire history as well as human land use and social cultural development across the region in depth.
We present a high-resolution isotope stratigraphy based on Globigerinoides ruber (white) over the past 2500 years in the Gulf of Taranto, central Mediterranean. G. ruber (white) reflects summer conditions in the Gulf of Taranto but is influenced by two major surface water masses: the Western Adriatic Current (WAC) and the Ionian Surface Water (ISW) and their variations on a decadal to multicentennial scale. Our analysis of the 13C and 18O of G. ruber (white) allows the distinction of several climatic periods: the ‘Roman Warm Period’ (RWP) (450–0 BC), with relatively wet and warm conditions and a higher influence of the WAC; the ‘Roman Classical Period’ (RCP) (AD 1–200) characterized by salinity increase resulting from circulation changes; the ‘Dark Ages Cold Period’ (DCP) (AD 500–750), where wetter conditions in the Gulf of Taranto region are coherent with an increase dominance of the WAC; the ‘Medieval Warm Period’ (MWP), with wet and warm conditions in the first, and a gradual drying in the second half; and finally, the transition from the MWP to the ‘Little Ice Age’ (LIA), which is characterized by continuing dry conditions.
A new sedimentary sequence from Lago di Venere on Pantelleria Island, located in the Strait of Sicily between Tunisia and Sicily was recovered. The lake is located in the coastal infra-Mediterranean vegetation belt at 2 m a.s.l. Pollen, charcoal and sedimentological analyses are used to explore linkages among vegetation, fire and climate at a decadal scale over the past 1200 years. A dry period from AD 800 to 1000 that corresponds to the ‘Medieval Warm Period’ (WMP) is inferred from sedimentological analysis. The high content of carbonate recorded in this period suggests a dry phase, when the ratio of evaporation/precipitation was high. During this period the island was dominated by thermophilous and drought-tolerant taxa, such as Quercus ilex, Olea, Pistacia and Juniperus. A marked shift in the sediment properties is recorded at AD 1000, when carbonate content became very low suggesting wetter conditions until AD 1850–1900. Broadly, this period coincides with the ‘Little Ice Age’ (LIA), which was characterized by wetter and colder conditions in Europe. During this time rather mesic conifers (i.e. Pinus pinaster), shrubs and herbs (e.g. Erica arborea and Selaginella denticulata) expanded, whereas more drought-adapted species (e.g. Q. ilex) declined. Charcoal data suggest enhanced fire activity during the LIA probably as a consequence of anthropogenic burning and/or more flammable fuel (e.g. resinous Pinus biomass). The last century was characterized by a shift to high carbonate content, indicating a change towards drier conditions, and re-expansion of Q. ilex and Olea. The post-LIA warming is in agreement with historical documents and meteorological time series. Vegetation dynamics were co-determined by agricultural activities on the island. Anthropogenic indicators (e.g. Cerealia-type, Sporormiella) reveal the importance of crops and grazing on the island. Our pollen data suggest that extensive logging caused the local extinction of deciduous Quercus pubescens around AD 1750.
Historical and documentary records from the Petit Lac d’Annecy, indicate that human activities have been the dominant ‘geomorphic process’ shaping the catchment during the late Holocene, with deforestation, agriculture and artificial drainage profoundly affecting both the pace and spatial distribution of soil erosion. The impact of past climatic change on the evolution of the catchment is less certain because of the lack of long-term climate records for the site. Previous attempts to use the sediment record from the lake to investigate the role past climate change may have played were hampered by the difficulty in isolating and disentangling the climatic signal preserved within the archive, because of overprinting of human activity. This is a common problem in regions with a long history of human activity in the landscape. In this study we use a range of novel statistical techniques (including cross-correlation and cross spectral analysis) to assess the relative importance of climate in driving landscape dynamics. The statistical analysis is carried out on an updated high-resolution palaeo-environmental data set from the Petit Lac d’Annecy. The results of the statistical analysis indicate that regional climate phenomena such as the Atlantic multidecadal oscillation are partly responsible for landscape dynamics at Petit Lac d’Annecy throughout the late Holocene. We find that the Petit Lac d’Annecy catchment typically requires decades, or longer, to respond to changes in precipitation, reflecting the stochastic nature of river sediment storage and transport. The use of a 4 yr integrated lake core record effectively attenuates the ‘signal shredding’ effect of shorter-term internally generated sediment transport processes. Nonetheless, the lake record of climatically induced geormorphic process–responses is weak compared with the pervasive impact of human activities.
This study focuses on the reconstructions of vegetation and climate changes during the past ~11,000 years on the basis of 222 fossil pollen samples from Qigai Nuur (core QGN-2004) in the southern part of the Mongolian Plateau. Plant Functional Type – Modern Analogue Technique was used for quantitative climatic reconstructions from fossil pollen data. Our results showed that regional vegetation experienced dramatic shifts between steppe forest and dry steppe before 9200 cal. yr BP in the Qigai Nuur region. The reconstructed mean annual temperature and especially mean annual precipitation also showed fluctuations at that time. From ~9200 to ~2800 cal. yr BP, the vegetation was dominated by steppe forests, and the reconstructed climate was generally warm and wet, but with two cold and dry intervals at ~7400 to ~6000 cal. yr BP and at ~4000 to ~2800 cal. yr BP. From ~2800 to ~850 cal. yr BP, dry steppe vegetation dominated the landscape under slightly cooler and much drier climate conditions. During the past ~850 years, the vegetation was characterized by abundant herbs and the climate showed rising temperature and fluctuating precipitation. The comparison of the reconstructed precipitation from the Qigai Nuur core with monsoon-strength records from southern China shows that the first-order variation in the precipitation was most likely controlled by the summer insolation-dictated Inter-Tropical Convergence Zone movements (i.e. N–S shifts). The comparison of the reconstructed precipitation from Qigai Nuur core with surface sea temperature in the Western Tropical Pacific Ocean suggests that the second-order variation in the precipitation was most likely modulated by the El Niño-Southern Oscillation dynamics (i.e. E–W shifts).
Tephra layers can form useful age-equivalent stratigraphic markers for correlating palaeoenvironmental sequences and they provide information about the spatio-temporal nature of past volcanic ash fall events. The use of microscopic ‘cryptotephra’ layers has both increased the stratigraphic resolution of tephra sequences in proximal areas and extended the distal application of tephrochronology to regions of the world situated far from volcanoes. Effective tephrochronology requires the discrimination between in situ tephra deposited directly from volcanic plumes and tephras that have been remobilised since their initial deposition. We present tephrostratigraphic and glass chemistry data from two proximal peat profiles (one lowland, one upland) from the Shetland Islands, UK. Both profiles contain the Hekla-Selsund tephra (deposited c. 1800–1750 cal. BC), whilst the Hekla 4 ash (c. 2395–2279 cal. BC) is present in the upland record. Overlying the Hekla-Selsund tephra are a number of distinct peaks in tephra shard abundance. The geochemistry of these layers shows that they represent re-working of the Hekla 4 and Hekla-Selsund layers rather than primary air-fall deposits. Pollen analysis of the peat sequences illustrates that these re-deposited tephra layers are coincident with a rise in heather-dominated vegetation communities (heath and/or moorland) and a subsequent intensification of burning in the landscape. We suggest that burning caused increased erosion of peats resulting in the remobilisation of tephra shards. The study demonstrates both the need for caution and the opportunities created when applying tephrochronologies in regions heavily affected by past human activity that contain both reworked tephra layers and in situ fallout.
Floodplain deposition rates have increased markedly under influence of human impact throughout the late Holocene in many western and central European catchments. Consequently the geomorphology and ecology of many floodplains changed. In this study we discuss this human impact and its influence on the floodplain geoecology during the middle and late Holocene for the headwaters of the Dijle catchment, located in the Belgian loess belt. The floodplain geoecology and the regional vegetation was reconstructed from sedimentological and palynological analyses. An age–depth model for the studied sequences was obtained using 17 radiocarbon dates. Statistical analyses of the pollen data (cluster analysis and canonical correspondence analysis) were used to detect changes in the pollen record. Our data show that until c. 2500 cal. BP, human impact was nearly absent or localized with no discernible influence on the floodplain geoecology. The floodplain was in a stable phase and consisted of a marshy environment where organic material could accumulate, which is interpreted as the natural state of the floodplain. From c. 2500 cal. BP onwards, human impact gradually increased. However, only when human impact in the catchment crossed a threshold around 500 cal. BP, the floodplain geoecology changed with clearing of the Alder carr forest, the establishment of a single channel river and the dominance of minerogenic overbank sedimentation. Spatial variability in the coupling between increasing human impact and changes in floodplain geoecology can be attributed to differences in hillslope–floodplain connectivity and local differences in human impact.
The environment of the northern taiga to tundra transition is highly sensitive to climate fluctuations. In this study from northeastern European Russia, stable carbon and oxygen isotope ratios (13C, 18O) in α-cellulose of Sphagnum fuscum stems subsampled from hummocks and peat plateau profiles have been used as climate proxies. The entire isotope time series, dated by lead (210Pb), caesium (137Cs) and AMS-radiocarbon (14C) dating, spans the past 2500 years. Plant macrofossil analyses were used as an aid in single species selection, but are also helpful in identifying past surface moisture conditions. The most significant relationships were found between the recent 13C record and summer (July–August) temperatures (R2 = 0.58, p < 0.01), and the recent 18O record and winter (October–May) precipitation anomalies in the tundra region (R2 = 0.36, p < 0.01). The study demonstrates that stable isotopes preserved in northern peat deposits are useful indicators for summer temperature and winter precipitation at decadal to millennial timescales.
Lake sediments from Lauenensee (1381 m a.s.l.), a small lake in the Bernese Alps, were analysed to reconstruct the vegetation and fire history. The chronology is based on 11 calibrated radiocarbon dates on terrestrial plant macrofossils suggesting a basal age of 14,200 cal. BP. Pollen and macrofossil data imply that treeline never reached the lake catchment during the Bølling–Allerød interstadial. Treeline north of the Alps was depressed by c. 300 altitudinal meters, if compared with southern locations. We attribute this difference to colder temperatures and to unbuffered cold air excursions from the ice masses in northern Europe. Afforestation started after the Younger Dryas at 11,600 cal. BP. Early-Holocene tree-Betula and Pinus sylvestris forests were replaced by Abies alba forests around 7500 cal. BP. Continuous high-resolution pollen and macrofossil series allow quantitative assessments of vegetation dynamics at 5900–5200 cal. BP (first expansion of Picea abies, decline of Abies alba) and 4100–2900 cal. BP (first collapse of Abies alba). The first signs of human activity became noticeable during the late Neolithic c. 5700–5200 cal. BP. Cross-correlation analysis shows that the expansion of Alnus viridis and the replacement of Abies alba by Picea abies after c. 5500 cal. BP was most likely a consequence of human disturbance. Abies alba responded very sensitively to a combination of fire and grazing disturbance. Our results imply that the current dominance of Picea abies in the upper montane and subalpine belts is a consequence of anthropogenic activities through the millennia.
Plaggen soils, formed by various vegetational inputs during century-long plaggen (i.e. sod) application, comprise remarkably stable organic matter. Source identification could contribute to a better understanding of carbon stabilization mechanisms in soils and reconstruction of Holocene vegetation and land-use history. Cuticular-derived n-alkane distribution patterns as present in current vegetation are recognized as valuable tools to discriminate input sources, but an assessment of their consistency and variability is lacking to date. Therefore, this review synthesizes information on published n-alkane patterns of vegetation species and their various parts that contributed to plaggen soil formation (i.e. Calluna vulgaris, Betula pendula, Quercus robur, Pinus sylvestris, Lolium perenne, Deschampsia flexuosa, Molinia caerulea and Poa annua). This provided in addition valuable information on potential sources of systematic variation (e.g. geography/climate, environmental conditions, ontogeny and seasonality). Method of extraction/analysis showed no evident effects on n-alkanes. n-Alkanes showed predominantly distinct patterns for different plaggen vegetation species and parts in the range C17–36. Prominent n-alkanes C27, C29, C31 and C33 allowed clear distinction between input by shrubs, trees and grasses to plaggen soils. Nevertheless, systematic variability was indicated among n-alkane patterns. Unfortunately, the current limited data set of n-alkane patterns did not allow for exact quantification of the controls of variation. The need for more systematic studies and the setup of a reference data base for vegetation species is highlighted to (1) advance application of n-alkane patterns in source identification, (2) gain more insight into controls on, magnitude and timing of variations and (3) improve our knowledge concerning input sources, carbon dynamics and stabilization mechanisms in (plaggen) soils.
The littoral site of Ifri Oudadane is one of the most important recently excavated sites in the Mediterranean Maghreb. The shelter presents Epipalaeolithic and Neolithic layers and therefore offers the possibility to investigate the Neolithic transition in the region. Besides introducing the archaeological context, this paper focuses on palaeobotanical data in order to reconstruct Holocene environmental change and human use of plant resources for the period c. 11 to 5.7 ka cal. BP. Results show intense landscape transformations resulting from anthropic and climatic factors. First human occupations start at the beginning of the Holocene with favourable conditions in this otherwise harsh semi-arid stretch of land. A wooded environment with evergreen sclerophyllous oaks and riparian forests is documented and exploited by hunter-gatherers. From c. 7.6 ka cal. BP farming activities are well attested together with significant human impact, herding pressure and a progressive decline of arboreal components. After 6.6 ka cal. BP conditions become less favourable and markers for aridity increase. Riparian taxa disappear (Alnus) or decrease (Fraxinus, Populus, Salix); shrubs (Tamarix) and grasses (Artemisia) increase with a degradation of forest into shrubland (macchia). During 6.6 and 6.0 ka cal. BP there is a general occupation gap in arid and semi-arid Morocco and evidence for that change is also found in the alluvial deposits of the Moulouya, NE Morocco. Indicators for food production decrease at the same time and the site is abandoned during the first half of the 6th millennium cal. BP.
Bomb-pulse dated mini moss-monoliths were used to determine modern pollen accumulation rates on mire surfaces at six locations in northern and central Norway. Coupled with vegetation data these were used to assess the modern pollen–vegetation relationships for Pinus, Betula and Poaceae. Preliminary absolute pollen productivity (APP) estimates are for Pinus sylvestris 11,300 ± 2300 (SE) grains/cm2 per yr, Betula pubescens 2200 ± 300 and Poaceae 1800 ± 200. The study suggests that pollen accumulation rates and absolute pollen productivity estimates can be derived from mire surface peat. This would ease the establishment of APP estimates for more taxa and regions than available today.
The objective of our research was to define the main human–environment interactions during the Neolithic period (6500–3700 BC) in the Apulia region of southeastern Italy based on available published and unpublished data. Knowledge of these interactions is crucial to understanding the cultural and social dynamics of the period, particularly concerning the earliest farmers. Using a multidisciplinary approach, paleoenvironmental and paleoclimatological data at the regional and Mediterranean scales were compared with the results of analyses performed on natural deposits and deposits in Neolithic settlements. The following data sets were used: (1) 121 14C dates for settlements, from which probability curves (%) of the Apulian Archaeological Occupation (AAO) were developed; (2) offshore data obtained from analyses performed on two offshore sediment cores drilled in the Adriatic Sea; (3) offsite data from studies conducted in two natural coastal contexts; and (4) onsite archaeobotanical data from 35 settlements. This study allowed us to tentatively define the main climatic features between 6200 and 3700 BC. We identified two dry phases (one between 5000 and 4600 BC and a second that peaked c. 4000 BC) and two wet intervals (one between 6200 and 5500 BC and a second that peaked around 4400 BC). Climate changes appear to have been relatively gradual. The use of archaeobotanical data allowed us to determine a direct link between paleoclimatic and archaeological sequences. These data highlight the variations in agricultural strategies (species used and harvest times) as humans responded to changes in the rainfall regime.
In recent decades the biometric analysis of shellfish resources (mainly marine mollusc shells) has been used by many researchers to support the hypothesis of their more intensive human use and to estimate the increase in human populations. This paper studies the plates of the crustacean Pollicipes pollicipes found in three Holocene archaeological levels at the Jaizkibel 3 shell-midden (Gipuzkoa, Basque Country, Northern Spain). First, by analysing a sample from each level, the Minimum Number of Individuals (MNI) was calculated from the Number of Remains (NR). Second, by using one of the plates (right scutum), the biometry of P. pollicipes in the three levels was reconstructed. The measurements are compared with a sample of P. pollicipes, collected a few kilometres away from the site of J3. The results indicate that the barnacles were not overexploited by the human groups.
To maximise the potential of the tree-ring isotopic signal for palaeoclimate research it is essential to understand and characterise the natural variability between individual trees. This study explores the nature of inter-tree isotopic variability and evaluates the implications for developing robust palaeoclimate reconstructions. We confirm levels of natural inter-tree variability similar to those reported in previous studies, but demonstrate, using a large data set of isotopic measurements determined from individual rings of 100 trees, that to obtain a representative regional environmental signal and to reduce problems when combining records, higher levels of replication than those typically adopted in isotope dendroclimatology may need to be considered.
We present a hydrogen isotopic record of long-chain n-alkanes in Lake Sugan to reconstruct regional moisture changes in the last 1700 years at a sampling resolution of 25 years. The D values decreased by over 30 from the ‘Medieval Warm Period’ (MWP; c. AD 600–1500) to the ‘Little Ice Age’ (LIA; c. AD 1500–1850), and indicated that the moisture pattern included a relatively humid climate before the MWP, becoming drier overall in the MWP, wetter in the LIA, and then tending towards drought in the post-industrial era. In the study region, Chenopodiceae shrubs were more abundant in dry climates than in wet. Meanwhile, D values of shrubs were more positive than those of grasses. Therefore, we suggest that the vegetation type (shrub or grass), which depends on moisture changes, is the controlling factor for D variations in Lake Sugan.
We present a ~9200 yr high-resolution oxygen isotope record of plant cellulose (18Ocel) from the peat deposits of Mer Bleue Bog, Ontario and apply it as a proxy for paleotemperature reconstruction in Eastern Canada. The results show that 18Ocel of Sphagnum follows the general pattern of the Northern Hemisphere reconstructed paleotemperature record for the last 2000 years at a ratio of ~218Ocel/°C. The 18Ocel record of ombrotrophic phase of Mer Bleue Bog is also in accordance with major features of the Holocene sunspot number reconstruction. Three distinct time intervals have low 18Ocel values: 200–800 cal. BP (‘Little Ice Age’); 2800–3400 cal. BP synchronous to a cooling period reported elsewhere in North America; and 4200–4600 cal. BP corresponding to a cooling interval in the North Atlantic region. These cooling periods also correlate well with negative excursions in the Holocene sunspot and cosmogenic 10Be records. A fourth period of low 18Ocel values between AD 1810 and 1820 may be related to the extremely cold summer of 1816 and cooler subsequent years, which occurred in the aftermath of the Tambora volcanic eruption, or possibly cooling associated with the early 19th century Dalton solar minimum. The results also indicate the presence of millennial-scale cycles possibly comparable with the globally recognized Bond cycles that have been correlated to fluctuations in solar irradiance.
Geological studies of past and present sea level rely on valid and robust features marking sea level in geological sections. Present sea-level markers around the upper shoreface to beachface transition are detected in a beach-ridge plain formed in a microtidal regime. These sea-level markers identify specific relative sea levels at the time of formation. Ground-penetrating radar (GPR) data collected across the youngest part of the beach-ridge system of Feddet, Denmark are compared with independent coastal morphological and sedimentological data of the active strand plain and interpreted in relation to sea-level data. The data show consistency between dip values of the present beachface and upper shoreface compared with dip values of interpreted beachface and upper shoreface GPR reflections. A clear change in dip value is observed between beachface and upper shoreface deposits in both data sets. Within few centimetres, this break point coincides with actual sea level and is interpreted to correspond to downlap points observed in the GPR reflection data. Furthermore, our observations may indicate that downlap points of deposits, formed under both relatively high and low water levels, are preserved and may be identified in GPR reflection data. Downlap points identified in GPR data across microtidal beach-ridge systems from other localities can also constitute markers of palaeo-sea level at the time of deposition. Records of these sea-level markers can be used to reconstruct the local relative sea-level history during the Holocene.
A palynological reconstruction (n = 25 profiles) suggests that the northern extent of lodgepole pine (Pinus contorta var. latifolia Engelmann ex S. Watson) occurred between 59° and 60°N latitude in northwest North America from 10,000 to 7000 calendar years before present (cal. yr BP) prior to entering Yukon. Although specific migration pathways could not be resolved with the available palynological data, mountains along the southern edge of Yukon appear to have diverted lodgepole pine migration through the Carcross and Frances Lake areas in southwest and southeast Yukon, respectively. Migration in the southwest (70 m/yr) was likely confined to lower elevations of the Yukon and Teslin river valleys, with lodgepole pine reaching 61°N ~2000 cal. yr BP. Along the eastern route, migration was channeled through a 15–20 km wide pass in a 200 km mountainous front. After breaching the Liard drainage divide north of Frances Lake ~4000 cal. yr BP, migration progressed northwest (160–220 m/yr) along the Tintina Trench. Lodgepole pine was estimated to have reached its near present-day northern limit (~63°N) ~1790 cal. yr BP, which is ~1290 years earlier than previously thought. This difference in arrival dates is due the use of a >5% rather than a >15% pine pollen content threshold, which appears to correspond with >1% pine tree cover in the landscape. Climatic cooling after 1000 cal. yr BP that caused a population decline at higher elevations is hypothesized to explain the present-day sparse and disjunct distribution of pine across Yukon north of 61°N.
An integrated multiproxy analysis from westernmost Mediterranean hemipelagic sediments has provided further insights into natural climate variability and forcing mechanisms in this region during the last two millennia. Two deep-sea marine records, with a robust age model provided by the activity–depth profiles of 210Pb and 137Cs, together with 14C dating, allowed us to perform a detailed reconstruction of paleoenvironmental and paleoceanographic responses during the ‘Medieval Climate Anomaly’ (MCA), the ‘Little Ice Age’ (LIA), the Industrial period (IP) and the second-half of the 20th century. Decreasing trends of fluvial-derived element (Si) and a increasing eolian input (Zr/Al ratio) characterized the MCA and the second-half of the 20th century as prevalent dry periods, while generally humid conditions are evidenced during the LIA and the IP, in accordance to a positive and a negative mode of the North Atlantic Oscillation (NAO), respectively (Trouet et al., 2009). The LIA developed as a sequence of successive short and abrupt dry–humid phase alternation. Furthermore, a noteworthy and sharp decrease of redox-sensitive elements (V/Cr and Ni/Co ratios) and coarser sortable silt at AD 1450 and 1950 yr, support more energetic hydrodynamic conditions at this time (oxygenated bottom waters and faster bottom currents), likely promoted by strengthened cooler waters flowing into the Mediterranean Sea.
A 19 m long sedimentary record retrieved in Lake Aydat (French Massif Central) covers the last 6700 yr at a high resolution. A multiproxy approach (density, magnetic susceptibility, XRF, Rock-Eval, pollen and non-pollen palynomorph analyses and a historical archives study) was used to characterise and propose a model of sedimentation. The high deposition rate results from the combined effects of the high suspension load of the river, autochthonous production and the narrow shape of the incised fluvial valley dammed by a lava flow c. 8550 years ago. Two contrasted periods (6700±200 to 3180±90 cal. BP, and 1770±60 cal. BP to present) were characterized. The lower unit (mid Holocene) displays a fine and regular lamination and holds a single, major, flood deposit. This unit is capped by an erosive mass-wasting deposit triggered c. 1770±60 cal. BP. The upper unit (late Holocene) is made of organic-rich and fine-grained faintly laminated sediment, with numerous interbedded flood deposits and diatom blooms. The sedimentation was principally controlled by climatic forcings until c. 1100 cal. BP, accompanied by detrital events linked to human activities around the lake. Then, a more detrital input attested by numerous and recurrent flood deposits can be linked to the intensification of a persistent anthropogenic impact on the catchment. Two phases of lake eutrophication are highlighted: 1200–1130 cal. BP, as a result of increased anthropogenic pressure, and the current phase that could have started c. 150 cal. BP.
Palaeoclimate-proxy data provide an invaluable source of evidence for past climatic conditions, which can be compared with data from climate model simulations. This study illustrates how high-resolution regional climate model simulations can be used to estimate the difference in the climate of New Zealand between 6000 years before present (yr BP) and the pre-industrial era (c. AD 1750). Four pairs (pre-industrial and 6000 yr BP) of atmosphere-only global and regional climate model simulations were run with prescribed sea surface temperatures (SST). The SSTs are derived from four different fully coupled ocean–atmosphere general circulation model simulations, resulting in a different lower-boundary forcing in each of the atmosphere-only simulations. We find evidence for generally cooler conditions and for wetter (drier) conditions over eastern (western) New Zealand 6000 yr BP. The work compares well with model and proxy estimates of temperature and precipitation in the New Zealand region between 7000 and 6000 yr BP. The results also highlight the added value of regional model studies in regions with such complex terrain as New Zealand. This study also shows the limitations of applying uniformitarian principles when downscaling global model fields (and ‘up-scaling’ palaeo-proxy data) to infer past climatic conditions.
This paper aims to evaluate the possible relationships between erosion intensity and changes in climate and land use during the past 5.5 cal. k years at Lake Lehmilampi, eastern Finland. In this study we compare a detailed geochemical sediment record with (1) forest and land use history inferred from the first pollen and charcoal records from Lake Lehmilampi, and (2) existing archaeological surveys and independent proxy-records of climate change in the study region. The physical and geochemical sediment parameters examined include grain size analysis data and 23 chemical elements, determined with four selective extractions and ICP-MS. There are indications of possible human impact in the lake catchment as early as the Neolithic period, c. 3000–2550 BC, but the first undisputable signs are dated to 1800–100 BC. Cereal pollen reappears at c. AD 1700 and increases rapidly until c. AD 1950. The Holocene Thermal Maximum, its end c. 2000 BC, and the ‘Medieval Climate Anomaly’ were major climate events that had a prominent effect on erosion intensity, while human impact was a more significant factor during the period 3000 BC–AD 800 and from AD 1500 onwards. Although signs of changes in erosion intensity found in the sediment were small in this small catchment, they were significant enough to have a clear impact on the fraction of potentially mobile element species. This fraction increases with decreasing erosion intensity, which is probably related to a higher degree of chemical weathering and leaching during periods of decreased erosion.