AMS 14C Dates Research Articles

What’s in a colluvial deposit? Perspectives from archaeopedology

Colluvial deposits are considered as sedimentary archives for the reconstruction of the sedimentation and climate history, past pedogenesis and phases of land use. However, the human contribution to the formation of colluvial deposits is mainly based on assumptions derived from the local chronostratigraphy and archaeology. For this reason, there is often a substantial gap in the identification of specific land use practices that promoted prehistoric soil erosion and sedimentation processes.We use an archaeopedological multi-proxy approach on a multi-layered colluvial deposit (six colluvial horizons) at the prehistoric site of Fürstenberg (Southwest Germany) to gain detailed insights into the sedimentation history, past pedogenesis and land use practices since the Neolithic. Soil and geochemical analyses such as X-ray fluorescence (XRF), X-ray diffraction (XRD), pedogenic oxides, pH-value and calcium carbonate content support the chronostratigraphy based on ages from optically stimulated luminescence (OSL) and AMS 14C dating. Further, biogeochemical analyses of phytoliths, charcoal spectra, black carbon (BC), soil organic matter (SOM) composition by using pyrolysis-field ionization mass spectroscopy (Py-FIMS), urease activity, steroid biomarker and heavy metals (HM) are used as land use proxies.The OSL and 14C ages and the local archaeological record indicate six phases of colluvial deposition that occurred through five phases of land use comprising the Early to Younger Neolithic, the Urnfield to Hallstatt period, the Iron to Roman Age, the High Middle Ages, and the pre-modern period. The soil and geochemical proxies correlate with a phase of geomorphodynamic stability between the Early to Younger Neolithic and the Urnfield to Hallstatt period. The high abundance of grass morphotypes since the Neolithic and the increase of Juniperus since the Urnfield to Hallstatt period indicate a persistent anthropogenic impact on the vegetation. Considerable amounts of burned OM (up to 676 g BC kg−1 SOC, also identified as thermally stabilized SOM compounds by Py-FIMS) in colluvial horizons provide information that fire clearing (e.g. slash-and-burn) was especially used to open and maintain the landscape until the Roman Age. The absence of phytolith species originating from cereals, the occurrence of Juniperus and the evidence from the analysis of urease activity and faecal biomarkers indicate that the slopes of the Fürstenberg were mainly used for livestock farming and wood procurement.Thus, the application of specific soil-biogeochemical proxies to colluvial deposits provide new information on the nature of past land use practices that caused the formation of colluvial deposits at that time. In general, archaeopedological multi-proxy analyses of colluvial deposits, integrating the local archaeological record, contributes to a refined understanding of how humans have shaped the landscape since the Neolithic.

Climate and ocean forcing of ice-sheet dynamics along the Svalbard-Barents Sea ice sheet during the deglaciation ∼20,000–10,000 years BP

The last deglaciation, 20,000–10,000 years ago, was a period of global warming and rapidly shrinking ice sheets. It was also climatically unstable and retreats were interrupted by re-advances. Retreat rates and timing relative to climatic changes have therefore been difficult to establish. We here study a suite of 12 marine sediment cores from Storfjorden and Storfjorden Trough, Svalbard. The purpose is to reconstruct retreat patterns and retreat rates of a high northern latitude marine-based ice stream from the Svalbard-Barents Sea Ice Sheet in relation to paleoceanographic and paleoclimatic changes. The study is based on abundance and composition of planktic and benthic foraminiferal assemblages, ice rafted debris (IRD), lithology, and 70 AMS-14C dates. For core 460, we also calculate sea surface and bottom water temperatures and bottom water salinity. The results show that retreat rates of the ice shelf and ice streams of Storfjorden Trough/Storfjorden (‘Storfjorden Ice Stream’) closely followed the deglacial atmospheric and ocean temperature changes. During the start of the Bølling interstadial retreat rates in Storfjorden Trough probably exceeded 2.5 km/year and more than 10,000 km2 of ice disappeared almost instantaneously. A similarly rapid retreat occurred at the start of the Holocene interglacial, when 4500 km2 of ice broke up. Maximum rates during the deglaciation match the fastest modern rates from Antarctica and Greenland. Correlation of data show that the ice streams in several fjords from northern Norway retreated simultaneously with the Storfjorden Ice Stream, indicating that temperature was the most important forcing factor of the Svalbard-Barents Sea Ice Sheet during the deglaciation.

Moisture evolution in Central Asia since 26 ka: Insights from a Kyrgyz loess section, Western Tian Shan

Central Asia (CA) is located in the hinterland of the Eurasian continent, and faces an extreme risk of continued aridification under the current global warming trend. To predict future climate change in CA, paleoclimate studies provide essential references. However, the mechanisms underlying climate changes in CA remain relatively poorly known. Here, we investigate moisture variations in CA, as recorded in a 6-m loess section in the Western Tian Shan, Kyrgyzstan, which has accumulated since ∼26 ka based on the radiometric AMS 14C dating. We reconstructed the evolution of the wind regime and moisture conditions in the Western Tian Shan with a modified grain size index (GSIm) and a new L∗ proxy (ΔL∗). While the frequency-dependent magnetic susceptibility (χfd), redness (a∗) and yellowness (b∗) did not provide reliable paleoclimatic indicators, due to weak pedogenesis and other controlling factors. The GSIm records demonstrated a precipitation maximum in summer before ∼15 ka, shifting to a maximum in spring after ∼15 ka, probably associated with large-scale modulation of the latitudinal climatic zones and atmospheric circulation in response to retreat of the Northern Hemisphere ice sheets. Based on the ΔL∗ records, we place emphases on the important role of temperature-modulated evaporation in moisture evolution across CA; however, this has only influenced moisture evolution in spring and summer, with little effect on winter moisture conditions. Moreover, the ΔL∗ records may also indicate that atmospheric humidity can partly affect the long-term effective moisture variations.

Sedimentary response to sea level and climate changes in the inner sea of Maldives carbonate platform over the past 30 kyr

We applied AMS 14C dates, Mg/Ca estimated sea surface temperature (SST), planktonic foraminiferal abundance, coarse component and X-ray diffraction mineral composition analyses for an International Ocean Discovery Program (IODP) sediment Hole U1467C in the Maldives inner sea, to reveal factors that affected the depositional process in the Maldives inner sea over the past 30 kyr. We found that the linear sedimentation rate (LSR) in Holocene (6.8 cm/kyr) was obviously higher than that in glacial period (3.45 cm/kyr); the average SST during the Holocene was 2–3°C higher than that in glacial stage. High abundance of planktonic foraminifera occurred during the glacial period, which was consistent with the variation of pelagic biogenic component. Reef-sourced material showed apparent high percentage during the Holocene (43.5%), in contrast to the low values during the glacial stage (20.7%). Terrigenous matter, only accounting for a small percentage in carbonate platform, was relatively high during the glacial period than that in the Holocene. We therefore conclude that reef-sourced material, dominated in the glacial-interglacial sediment sources, was mainly affected by sea level and climate changes. During glacial stage, sea level low-stand and weakened weathering in Maldives limited the input of the eroded material into the inner sea, resulting in low LSR; while the Holocene high sea level accompanied with rapid growth of the reef atoll and enhanced weathering, brought more reef-sourced material to the inner sea, leading to increased LSR and lowered abundance of planktonic foraminifera. The sea level and climate-controlled reef-sourced material changes are the key to understand the sedimentary process of the Maldives inner sea. Our study will shed some light on the evolution of glacial-interglacial sedimentary process of carbonate platform.

Lake Heimtjønna at Dovre, Mid-Norway, reveals remarkable late-glacial and Holocene sedimentary environments and the early establishment of spruce (Picea abies), alder (Alnus cf. incana), and alpine plants with present centric distributions

Two and a half meters of sediments from Lake Heimtjønna in the Scandes Mountains reveal changes in the vegetation, climate, and sediment environment since deglaciation. The lake was deglaciated in the Late-Glacial (LG), perhaps as early as 16-18 ka cal BP. After deglaciation, the sediment environment at the Heimtjønna coring point was extraordinary and challenging to interpret. The genesis of the 1.7 m basal unsorted sediments including large stones is discussed concluding that the layer was rafted by lake-ice after the LG deglaciation. The Younger Dryas (YD) established a semi-perennial lake-ice that stopped the deposition of the ice-rafted stone-rich sediments. In the early Holocene, the unstratified and well-sorted clayey silt shows fluvial origin. In late Holocene, strong flood activity including the major flood disaster ‘Stor-Ofsen’ in AD 1789, caused a sediment hiatus at the coring point from ca 9.5 ka cal BP to ca 250 a cal BP. The LG interstadial warming initiated the succession from pioneer plants on mineral soils towards local dwarf-shrub heath. July temperatures reached at least 7–8 OC. In the LG and early Holocene, Papaver radicatum, Artemisia norvegica, and Campanula cf. uniflora today occurring at Dovre and with centric Scandinavian distributions, locally established. All have previously been connected to Weichselian survival on nunatak refugia. Continuous pollen curves of spruce (Picea abies) support the much-debated LG and early Holocene presence of spruce in the Scandes mountains. For the first time, it is shown that both grey alder (Alnus incana) and Armeria occurred in the Scandes in the LG and early Holocene. Due to dating errors, LG ages is exclusively based on stratigraphical correlations and considerations. The LG chronology must be thoroughly tested by future studies providing reliable AMS 14C-dates of terrestrial fossils.

Bronze Age Wool Textile of the Northern Eurasia: New Radiocarbon Data

The Bronze Age of northern Eurasia is characterised by major socio-economic changes. A secondary products revolution defined an overall trajectory in these global economic transformations. Innovative changes in fibre technologies led to the appearance of woven wool textiles and the production and consumption of new types of garment. Analysis of the first direct AMS 14C dates from woven wool fibres from Bronze Age sites across northern Eurasia allow us to define key stages in the directional spread of woven wool textiles and to determine the cultural context of this process of technological transmission.

Holocene paleoenvironmental changes in mud area southwest off Cheju Island, East China Sea: Evidence from benthic foraminiferal assemblages and stable isotope records

A sediment core retrieved from the mud area southwest off Cheju Island (MASCI) was analysed for benthic foraminifera, grain size, and stable isotopes and constrained by AMS14C dating. Holocene paleoenvironmental changes in this broad shallow shelf were investigated, with special focus on the evolution of the MASCI and its related ocean eddy system. The results indicate that the East China Sea shelf has undergone four major environmental evolution stages during the Holocene. Prior to 9.8 cal. Kyr BP, the benthic foraminiferal assemblages were dominated by low salinity, shallow-water species [Ammonia beccarii (Linnaeus), Elphidium advenum (Cushman), and Cribrononion subincertum (Asano)], reflecting a near-coast-deposit environment. A noticeable transition of the benthic foraminifera, from an A. beccarii dominated to Ammonia compressiuscula (Brady) dominated assemblage, taking place at approximately 9.8 cal. Kyr BP together with a contemporaneous increase in δ18O and δ13C, provides evidence that a rapid rise in sea level occurred at this time in the East China Shelf. A gradual increase in δ18O between 9.8 and 6 cal. Kyr BP indicates a steady strengthening influence of open ocean water on the area under study. A sudden increase in the abundance of benthic foraminifera along with a decrease in the coarse fraction imply that an early eddy circulation system was established since almost 6 cal. Kyr BP in the MASCI. This eddy circulation system was quite weak but gradually strengthened between 6 and 3 cal. Kyr BP, possibly due to the intrusion of the Yellow Sea Warm Current (YSWC). A more stable mud deposition period, characterised by a high sedimentation rate of fine-grained sediment and lighter value of δ13C, starting at approximately 3 cal. Kyr BP, indicates that the MASCI was formed mainly during the late Holocene. We believe that the strengthened YSWC since 3 cal. Kyr BP might increase the trap efficiency of the eddy system, thereby accounting for the high sedimentation rate of mud deposits during this period.

New AMS 14C dates track the arrival and spread of broomcorn millet cultivation and agricultural change in prehistoric Europe

Broomcorn millet (Panicum miliaceum L.) is not one of the founder crops domesticated in Southwest Asia in the early Holocene, but was domesticated in northeast China by 6000 bc. In Europe, millet was reported in Early Neolithic contexts formed by 6000 bc, but recent radiocarbon dating of a dozen 'early' grains cast doubt on these claims. Archaeobotanical evidence reveals that millet was common in Europe from the 2nd millennium bc, when major societal and economic transformations took place in the Bronze Age. We conducted an extensive programme of AMS-dating of charred broomcorn millet grains from 75 prehistoric sites in Europe. Our Bayesian model reveals that millet cultivation began in Europe at the earliest during the sixteenth century bc, and spread rapidly during the fifteenth/fourteenth centuries bc. Broomcorn millet succeeds in exceptionally wide range of growing conditions and completes its lifecycle in less than three summer months. Offering an additional harvest and thus surplus food/fodder, it likely was a transformative innovation in European prehistoric agriculture previously based mainly on (winter) cropping of wheat and barley. We provide a new, high-resolution chronological framework for this key agricultural development that likely contributed to far-reaching changes in lifestyle in late 2nd millennium bc Europe.

Lake-Level Oscillation Based on Sediment Strata and Geochemical Proxies Since 11,000 Year From Tengger Nuur, Inner Mongolia, China

A 794-cm section and core from Tengger Nuur (42°27´N, 110°42´E) in the Inner Mongolia Plateau had been collected. 8 effective AMS 14C data had been determined to set an age-depth model after minus about 1920 years carbon reservoir effective. Based on the multi-proxies grain size, carbonate-content, TOC-content, ratios of Mg/Ca and Sr/Ca, and carbonate carbon and oxygen isotope, palaeoenvironmental change had been reconstructed since the last deglacial. Tengger Nuur was very shallow during the last deglacial under cool and wet climate, especially much shallower at interval cold YD event. Although, temperature and humidity increased from the early Holocene ~10500 to 8750 cal a BP, low lake-level indicated that summer monsoon did not strengthen the modern monsoon boundary in Inner Mongolia. High monsoon precipitation made lake to expand during 8750~5000 cal a BP, but lake-level oscillated in a shallow state under higher evaporation. A low lake-level event interrupted with the cold-wet climate at interval 5450~5100 cal a BP. Summer monsoon receded gradually to keep a deep lake under high effective humidity during 5000~2000 cal a BP, and low lake-level events punctuated at intervals 4300~3980 cal a BP and 3700~2750 cal a BP. Lakes shrank gradually to be salinization or completely desiccation in the cold and dry westerly after 2000 cal a BP, but oscillated much lower lake-levels at four periods of 1900~1740 cal a BP, 1500~1050 cal a BP, 550~400 cal a BP (Little Ice Age), 100 cal a BP ~AD 1985. A weak eastern summer monsoon was in the early Holocene, and lake-level oscillation was controlled by the effective humidity in the arid and semi-arid area.

Bioerosion on Late Quaternary Planktonic Foraminifera Related to Paleoproductivity in the Western South Atlantic

AbstractPlanktonic Foraminifera are widely used in paleoceanographic reconstructions, although studies of their trophic interactions are still rare, especially those focusing on predation. Drilling holes are the most frequent traces of bioerosion in foraminifer tests, but environmental factors that control bioerosion are not yet understood. To determine if paleoceanographic variables are associated with bioerosion rates in late Quaternary planktonic foraminifers of the western South Atlantic, geochemical and assemblage analyses were made on a 46 kyr record from a piston core. An age model was constructed based on 10 AMS 14C dates. To reconstruct the paleoproductivity, δ13C, benthic/planktonic foraminifer and the relative abundances of Globigerina bulloides and Globigerinoides ruber (high and low productivity, respectively) were used. Bioeroded tests were counted and found in 21 of the 25 identified species, with frequencies ranging from 8.84% to 16.7%. Bioerosion was different in two groups identified by cluster analysis, with a higher intensity during glacial times, showing a strong correlation with paleoceanographic fluctuations. Paleoproductivity estimates and bioerosion rates show a significant correlation, suggesting that bioerosion is more frequent in eutrophic environments and more inhibited in oligotrophic conditions. However, even with a strong correlation between bioerosion and productivity, there is also a negative correlation with sea surface temperature in the study area. Since conditions that promote higher productivity are accompanied by a decrease in surface temperature, the precise distinction between the influence of both variables is hampered. Further research will allow us to explore the potential of planktonic foraminiferal bioerosion as a tool in paleoceanographic studies.

Evidence of Abrupt Climate Change during the Mid‐ to Late‐Holocene Recorded in a Tropical Lake, Southern China

AbstractResearch on abrupt paleoclimatic and paleoenvironmental change provides a scientific basis for evaluating future climate. Because of spatial variability in monsoonal rainfall, our knowledge about climate change during the mid‐ to late‐Holocene in southern China is still limited. We present a multi‐proxy record of paleoclimatic change in a crater lake, Lake Shuangchi. Based on the age‐depth model from 210Pb, 137Cs and AMS14C data, high‐resolution mid‐ to late‐ Holocene climatic and environmental records were reconstructed using multiple indices (TOC, TN, C/N, δ13C and grain size). Shuangchi underwent a marked change from a peat bog to a lake around 1.4 kaBP. The C3 plants likely dominated during 7.0–5.9 ka and 2.5–1.4 kaBP, while C4 plants dominated between 5.9–3.2 and 3.0–2.5 kaBP. Algae were dominant sources of organic matter in the lake sediments after 1.4 kaBP. Several intervals with high concentrations of coarser grain sizes might be due to flood events. These results reveal that several abrupt paleoclimatic events occurred around 6.6 ka, 6.1 ka, 5.9 ka, 3.0 ka, 2.5 ka and 1.4 kaBP. The paleoclimatic change recorded in the lake may be related to the migration of the Intertropical Convergence Zone (ITCZ) and El Niño ‐ Southern Oscillation (ENSO) activity.

ENHANCED AEOLIAN ACTIVITIES IN THE MIDDLE YANGTZE RIVER BASIN DURING MIS2: EVIDENCE FROM RADIOCARBON DATING OF SAND HILLS AND LOESS SEDIMENTS

ABSTRACTAeolian deposits are widely distributed in the middle Yangtze River Basin (YRB), central China. The formation of those aeolian deposits (including aeolian sands and loess deposits) represented the deterioration of local environment. Previous geochronological studies have shown that both aeolian sands and loess began to be deposited in the last interglacial (~100 ka). In this study, a total of four and six accelerator mass spectrometry radiocarbon (AMS 14C) samples were collected from a sand hill and a loess section, respectively, in the Jiujiang area to refine their chronology. Charcoals extracted from bulk samples were employed for AMS 14C dating. The sand layer at the lower part of the HG-C section is sandwiched by two mud layers dated to 26,670–26,285 and 24,480–24,180 cal BP, respectively. Therefore, we infer that aeolian activities in this region started at ~25 ka BP, which was significantly younger than that of previous studies. Meanwhile, thick loess began to deposit leeward of the sand hills in this region. Based on the AMS14C chronology and provenance tracing, we conclude that the loess was essentially the fine-grained aeolian deposits. Our results suggest that topography and vegetation cover have an important effect on the spatial distribution of aeolian deposits in this region.

AMS 14C Dating Problem and High-Resolution Geochemical Record in Manzherok Lake Sediment Core From Siberia: Climatic and Environmental Reconstruction for Northwest Altai Over the Past 1,500 Years

This study presents high-resolution multi-proxy biological and geochemical records in an 82-cm sediment core from Manzherok Lake located in forest-steppe zone on western piedmonts of Altai Mountain, Russia. Based on 210Pb dating and 48 AMS 14C dates as well as pollen data and geochemical proxies, detailed lake history and local climatic changes over the 1500 years are obtained. Prior to Medieval Warm Period (MWP), the lake had high productivity under stable moderately wet and warm conditions. During 1150~1070 yr BP, strong surface runoff led to high detritus input and increasing lake level, reflecting onset of MWP. The lake was deep and fresh under warm and wet conditions of MWP (1070~ 850 yr BP). In this interval, more aquatic algae and submerged plants on the lake bottom were generated, which would use dissolved CO2 partially decomposed from organic matters in the deeper sediment layers. Consequently, many ABA treated samples contain old carbon influence on their 14C dates. This calls for attention on chronological construction of lake sediments. During 850~700 yr BP, the lake level started to drop with reduced sediment load under cooling and drying conditions. Low sedimentation and lake productivity occurred due to cold and dry climates during 700~500 yr BP. Very low sedimentation and hiatus were attributed to ice cover and weak water input between 500 and 50 yr BP corresponding to cold and dry Little Ice Age. Manzherok Lake has recovered productivity and deposition during the current warming century. Change in the total solar irradiance (TSI) is an important factor to influence climate in the Altai Mountains. With decreased TSI, Siberian High became strong, which led to Westerly and polar front be pushed away from this region, resulting arid climates. The situation was reversed vice versa.

High-resolution palaeomagnetic record from Sea of Marmara sediments for the last 70 ka

SUMMARYMagnetostratigraphic and geochemical analyses were performed on two sediment cores recovered from the Sea of Marmara to investigate geomagnetic field variations over the last 70 ka. A chronology for each of the two cores was developed from eight AMS 14C datings, tephrochronology, and tuning of Ca concentrations with stadials and interstadials observed in Greenland ice core oxygen isotope data. Based on the age models, cores MD01–2430 and MRS-CS19 reach back to 70 and 32 ka, respectively. High average sedimentation rates of 43 cm kyr–1 for core MD01–2430 and 68 cm kyr–1 for core MRS-CS19 allow high-resolution reconstruction of geomagnetic field variations for the Sea of Marmara. Mineral magnetic properties are sensitive to glacioeustatic sea level changes and palaeoclimate variations in this region, reflecting the variable palaeoenvironmental conditions of the Sea of Marmara during last 70 ka. Despite the impairment of the palaeomagnetic record in some stratigraphic intervals due to early diagenesis, relative palaeointensity variations in the Sea of Marmara sediments correlate well with similar records derived from other regions, such as the nearby Black Sea and the GLOPIS-75 stack. The directional record derived from the Sea of Marmara cores exhibits typical palaeosecular variation patterns, with directional anomalies at 41 and 18 ka, representing the Laschamps and postulated Hilina Pali excursions, respectively. Both directional anomalies are also associated with palaeointensity minima. A further palaeointensity minimum at 34.5 ka is likely related to the Mono Lake excursion, with no directional deviation documented in the Sea of Marmara palaeomagnetic record so far.

Historical change of carbon burial in Late Quaternary sediments of the ancient Yellow River delta on the west coast of Bohai Bay, China

The ancient Yellow River Delta (YRD) on the west coast of the Bohai Bay is possibly a huge carbon sink due to the high runoff and sediment load of the Yellow River, which transfers huge amounts of particulate carbon from terrestrial sources to the Bohai Sea. In this study, a 30.76 m long core (BXZK11), drilled in 2016, has been analyzed for AMS 14C dating, grain size, foraminifera, organic carbon (OC), total nitrogen (TN), and stable carbon isotope ratios (δ13C) to provide insights into the historical changes of carbon burial in Late Quaternary sediments of the ancient YRD. The results show that the sedimentary environments are divided into six depositional units in core BXZK11. The biggest contributor to organic carbon apparent mass accumulation rate (OCAMAR) is the negative covariance between apparent sedimentation rate (ASR) and OC. The average of OCAMAR is 20.76 g/(m2 yr) during the Holocene. The rates are highest in delta front deposits and lowest in shallow sea environments. Compared with the modern YRD, BXZK11 exhibits rather low ASR and OCAMAR, indicative of the enormous variations of Yellow River sediment load into the sea and the significant difference of carbon sequestration capacity of YRD at different periods. C3 plants of the delta wetland gradually develop without C4 plant input as the delta transgresses after sea level stabilization. The sediments have been characterized by decreasing terrestrial organic matter (TOM) since 6500 cal. a BP, reflecting the decline of Yellow River freshwater discharge. Both the 8.2 ka event and the weak Asian monsoon summer event at 6265 cal. a BP correspond well with the low TOM in BXZK11. The implication is that climate may affect the dynamics of carbon burial by regulating terrestrial inputs.

Temperature-induced dry climate in basins in the northeastern Tibetan Plateau during the early to middle Holocene

Ongoing global warming will have a significant impact on terrestrial water resources, especially in arid and semi-arid regions. Assessing changes in the hydrology and water resources in inland basins under a warm climate in the recent geological past can provide a valuable context for assessing their current and possible future status. Here we present a record from a rapidly-accumulating sediment core from Lake Dalianhai in the Gonghe Basin in the northeastern Tibetan Plateau. The chronology of the uppermost 51.63 m of the core is based on AMS 14C dates from 11 samples of terrestrial plant microfossils and 14 bulk samples. Hydroclimatic variations within the basin during the last 23,000 yr were reconstructed from sedimentological and geochemical parameters and paleoshoreline records. The results indicate that the Gonghe Basin experienced relatively arid conditions during 23,000-14,700 cal yr BP. Lake Dalianhai was refilled at 14,700 cal yr BP and a high lake level was sustained until the beginning of the Holocene, as indicated by changes in the concentration of OH-GDGTs. However, the lake level was low during the early to middle Holocene (11,700-4700 cal yr BP) and increased during the late Holocene. Based on a comparison with lake level records and aeolian sand deposits from the region, we conclude that the climate was extremely dry in basins in the northeastern Tibetan Plateau during the early to middle Holocene. We propose that strong evaporation combined with high summer temperatures during the early to middle Holocene were responsible for the dry climate at that time, rather than changes in mid-latitude precipitation. Given the situation occurred during the early to middle Holocene, ongoing global warming may seriously threaten water resources in inland China, even if precipitation increases substantially.

Diatom evidence for mid-Holocene peatland water-table variations and their possible link to solar forcing

Peatlands located at the northern edge of the East Asian monsoon (EAM) are well placed to provide a terrestrial record of past climate and hydrological changes for this globally sensitive region. Here we present a middle to late Holocene, diatom-derived water-table records from a peatland in the Greater Hinggan Mountains, northeastern China. An age-depth model was achieved through AMS14C dating and Bayesian piece-wise linear accumulation modelling. The diatom-based water-table reconstructions show that the peatland water-table rose from 5100 to 3500 cal. yr BP, but fell approximately 3500 cal. yr BP. From about 2800 to 1500 cal. yr BP, the peatland water-table stabilized. After about 1500 cal. yr BP, several rapid hydrological shifts, which correspond with global climate anomalies such as ice-rafted debris (IRD) events, were registered in the reconstructed water-tables. Compared with other paleoclimate records in East Asia, the general trend of peatland water-table fluctuations follows the variations in the East Asian summer monsoon (EASM) intensity. Spectrum analysis of the water-table profile yielded a statistically significant periodicity of 470-year that may be related to the “~500-year” inherent solar irradiation cycles. In addition, positive correlation between the peatland water-table levels and cosmic-isotope-reconstructed sunspot numbers underscores the role of the sun in regulating hydrological processes in the EASM margin area. The data suggest that the regional climate and hydrological variations at the EASM margin were first triggered by changes in solar output, but may have been amplified by interactions with oceanic and atmospheric circulations.

Spatial patterns of temperature, precipitation, and settlement dynamics on the Iberian Peninsula during the Chalcolithic and the Bronze Age

In light of recent climate changes, it is important to also gain knowledge about the spatial manifestation of past climate events and their potential impact on ancient societies across a wide range of different scenarios. Following this approach, we compare compilations of seasonal (winter and summer) as well as annual precipitation and temperature changes to a measure of human activity based on AMS 14C data of settlement sites from the Iberian Peninsula during the Chalcolithic and the Bronze Age – a period of major social turnover. Palaeoclimatic reconstructions show a long-term decrease in winter precipitation between 6000 and 3000 cal. BP (4050–1050 BCE). Superimposed to this long-term aridification trend was the 4.2 ka BP climate event, which manifested itself as a period of abrupt decrease in summer precipitation and/or an elongation of the summer dry period, but probably with constant winter precipitation from 4000 to 3800 cal. BP (2050–1850 BCE), particularly affecting the southeast of the Iberian Peninsula. Additionally, a winter cooling event across the Iberian Peninsula and its marginal seas occurred between 4400 and 4000 cal. BP (2450–2050 BCE) coinciding with Bond Event 3. By comparing human activities to the changes in seasonal and annual precipitation, new insight is gained into the causal relationships between climatic and social dynamics in the past. We show that winter precipitation potentially played a major role for the societies during the Chalcolithic and the Bronze Age of the southern Iberian Peninsula. While the El Argar culture at the south-eastern Iberian Peninsula boomed in spite of enhanced summer drought associated to the 4.2 ka BP climate event, decreasing winter precipitation was potentially contributing to a demographic decline in the southwest after 4800 cal. BP (2850 BCE) as well as to the bust of the El Argar culture in the southeast after 3600 cal. BP (1650 BCE) by limiting the agricultural strategies.

Vegetation evolution-based hydrological climate history since LGM in southern South China Sea

Abstract The reconstruction of vegetation evolution and climate changes at low latitudes since the Last Glacial Maximum (LGM) remains incomplete. In this study, we reconstructed the palynological history of vegetation changes since the LGM using a sediment core collected from the slope in the southern South China Sea (SCS). The chronology of the core was based on eight AMS14C dates, and 85 stratigraphic samples were palynologically analyzed. Our results denote that the vegetation reconstructed during the LGM in the southern SCS was characterized by a relatively high percentage of herb pollen and a modest decrease in the number of fern spores, suggesting a temperature decline and humidity change in this region. Further, the preservation of a rich diversity of pollen from the tropical lowland rainforest indicated that the rainforests might have covered large areas of the exposed Sunda Shelf during the LGM. The dynamic concentration of the Pinus pollen in the core, which is a proxy for the East Asian winter monsoon (EAWM), satisfactorily matched the changes in the Atlantic meridional overturning circulation and Australian-Indonesian summer monsoon, especially during the Heinrich Stadial 1. This suggests that the climate at the high latitudes of the Northern Hemisphere can drive the Intertropical Convergence Zone (ITCZ) southwards based on the enhanced EAWM. The southward-shifting ITCZ may change the hydrological climate of the equator and the Southern Hemisphere. The pteridophyte spores, which are good regional precipitation indicators, were positively correlated with the warm pool convection and inversely related with the EAWM, possibly indicating the considerable impact of the high-latitude climate in the Northern Hemisphere on precipitation in the tropical regions. Our results indicate that during the last deglaciation, the tropical hydrological changes were relatively moderate when compared with the drastic change observed at high latitudes and were attributed to the regulation of the El Nino-Southern Oscillation-like state. Our sequence of pollen and spores from the southern SCS can be used to observe the detailed dynamics of climatic evolution in tropical regions. The results of this study are essential to understand the complicated climate processes and the relation between high and low latitudes.

Prehistory of Košice – settlement in the Neolithic

This article presents the results of archaeological excavations at the sites Košice-Galgovec I-III and Červený rak on the southeastern edge of Košice in 1997–2001 indicated several stages of settlement and their dating. AMS 14C dates for the Tiszadob group were 6260±35 BP, 5330–5140 calBC; for the early stage of the Bükk culture they were 6310±40-35 BP, 5285±42 calBC. Assessment of residential, farming and settlement features was carried out, and numerous remains of pottery and lithic industry were classified with regard to contemporary sites in the Košická kotlina basin and in northeastern Hungary. The researchers evaluated the settlement in the microregion of Košice from the beginning of the Eastern Linear Pottery culture – the Proto-Linear stage – to the Barca III group and the Tiszadob group and the subsequent settlement during the Bükk culture period.