AMS 14C Research Articles

Metal tools of the Petrovka Culture of the Southern Trans-Urals and Middle Tobol: chemical and metallurgical characteristics

In this paper, the chemical composition of tools and ingots of the Petrovka Culture of the Southern Trans-Urals and Middle Tobol region is characterized with identification of main recipes of the alloys using several analytical methods (spectral, X-ray fluorescence, and atomic emission spectrometry analyses carried out in the laboratories of the Institute of Archaeology of the Russian Academy of Sciences and the Institute of Inorganic Chemistry of the Si-berian Branch of the Russian Academy of Sciences). The complexes of the Petrovka Culture of the Sou-thern Trans-Urals have been dated by a set of AMS 14C dates to 19th–18th centuries BCE. Recently introduced in the scientific discourse 27 AMS 14C dates (settlement of Stepnoe and burial grounds of Stepnoe 1, 7 and 25) established an ear-lier interval of the Petrovka series — 2133–1631 BCE and point to the synchroneity of the cultures at the northern periphery of the Sintashta area in the local micro-region of the Southern Trans-Urals. The results of the analytical study of 106 metal tools and 70 ingots of the Petrovka Culture of the Southern Trans-Urals and south of Western Siberia are reported. The statistical processing of the analytical results with plotting correlation diagrams of Sn–As, Sn–Pb, As–Ag, As–Sb, and a frequency distribution histogram for the proportions of Sn allowed casting the metal into 4 metallurgical groups — pure copper and tin, arsenic-tin and arsenic bronzes. The first group subdivided into oxide and sulfidic samples. According to the geochemical peculiarity of the metal from the metal industry centers of Ustie 1, Kulevchi 3 and Shibaevo 1, several sources of oxide-carbonated ores were utilized for copper smelting — malachite and azurite-malachite deposits, while sulfidic chalcocite-covelline ores, and sometimes chalcopyrite-pyrite depositions, were added to the melt as a flux agent. The admixture of sulfides was carried out as an experiment and was not purposeful. Petrovka metallurgists supplied copper to the workshops of the Middle Tobol region — the sites of Ubagan 1, 2, 3 and Kamyshnoe 1, 2. The centers of the Petrovka Culture of the Southern Trans-Urals were domi-nated by the production of pure copper implements, including the metal smelted from the oxidized ore. To a lesser extent, low-alloyed bronze was used — Cu+Sn, Cu+Sn+As and Cu+As, whose feedstock was supplied by the kin-dred tribes of Central and Eastern Kazakhstan in the form of ingots and finished products along the eastern part of the Trans-Eurasian transport corridor of metal trade — over the Turgay trough and further along the extensive river system of the Tobol River and its tributaries. The highest concentration of tools of alloyed bronzes was recorded in the burial grounds of the Middle Tobol, which can be explained from the point of view of the prestige value of such goods and observance of special ceremonial practices.

Effective Moisture Evolution since the Last Glacial Maximum Revealed by a Loess Record from the Westerlies-Dominated Ili Basin, NW China

Moisture variation is extremely relevant for the stability of ecosystems in Central Asia (CA). Therefore, moisture evolution and its potential driving mechanism over the region are always a hot research topic. Although much effort has been devoted to understanding the processes of moisture evolutions in CA during the Quaternary, particularly the Holocene, the associated underlying mechanisms remain in a state of persistent debate. In this study, the granulometry, clay mineral and chroma properties of a loess section (named ZSP section) in the westerlies-dominated Ili Basin, NW China are investigated. With the accelerator mass spectrometry radiocarbon dating (AMS 14C)-based Bayesian age–depth model, we provide a sensitive record of effective moisture evolution since the last glacial maximum (LGM) in the basin, and the results help enhance understanding of the possible driving mechanisms for westerly climate change. Comparisons of clay mineralogy indices shows that the study area is involved in the Northern Hemisphere dust cycle processes as a dust source, and the content of <2 μm grain size fraction in the ZSP section can thereby be used to reflect the westerlies’ intensity. After deducting the complicated influencing factors for lightness changes throughout the section, the calibrated lightness is adopted to indicate the regional effective moisture. Our findings show that effective moisture is relatively abundant during the LGM and the middle–late Holocene, with dry climate conditions during the last deglaciation and early Holocene. We argue that westerlies’ intensity was the main factor for driving the effective moisture evolution in the Ili Basin since the LGM. Local and source evaporation intensity and effective intra-annual control time of the westerlies over the study area exerted a minor influence on the moisture changes.

Single-grain K-feldspar pIRIR dating of the Shalongka archeological site revealed the relationship between monsoon, overbank flooding, and human occupation during the Holocene on the northeastern Tibetan Plateau

The increased frequency of flooding on the Tibetan Plateau as a result of global warming has affected the lives of millions of people along the river valleys. The relationship between human settlement, climate change, and the frequency of flooding at long time scales is still unclear primarily due to the lack of a robust chronology for flooding deposits. In this study, AMS 14C dating, single-grain quartz OSL dating, and single-grain K-feldspar pIRIR dating using pIR50IR170 and pIR200IR290 signals were applied to the fluvial-paleosol sequence at the archaeology site Shalongka (SLK20) in the upper Yellow River valley on the northeastern Tibetan Plateau, where Paleolithic, Neolithic, and Bronze Age cultural layers were found. Utilizing luminescence characteristics analysis and a comparison of quartz OSL ages, K-feldspar pIRIR ages, and charcoal 14C ages, the reliability of single-grain quartz OSL and K-feldspar pIRIR ages was tested. Our results indicate that single-grain K-feldspar pIRIR170 dating with the minimum age model (MAM) can be used to date Holocene fluvial deposit that have been poorly bleached. Based on the age-depth model, proxy data of the SLK20 grain size and magnetic susceptibility demonstrate that Yellow River overbank flooding increased during the periods 9.9–9.1, ∼8.0, 7.6–6.3 and 5.0-3.4 kyr BP; during the intervals between these periods, Yellow River overbank decreased and paleosols developed. Human occupations, as indicated by the appearance of cultural layers at the SLK20 site during the ∼8.1, ∼7.8, 6.3–5.0 and 3.4–2.0 kyr BP periods, occurred when paleosol developed. The variation in East Asian summer monsoon (EASM) intensities caused a moist and warm mid-Holocene climate at the SLK20 site, which was conducive to human settlement. Flood events caused by EASM precipitation changes during the mid-Holocene significantly influenced human settlement at the SLK20 site. During the middle to late Holocene, as EASM decreased in the region, the improvement of subsistence strategies likely dominated human settlement on the northeastern Tibetan Plateau.

The domestic dog that lived ∼17,000 years ago in the Lower Magdalenian of Erralla site (Basque Country): A radiometric and genetic analysis

Dogs are known to be the first species domesticated by humans, although the geographic and temporal origin of this process is still under debate in different fields of knowledge. In the present study, we examined a humerus from a canid recovered in the Lower Magdalenian level of the site of Erralla (Zestoa, Gipuzkoa, Basque Country, Spain), combining morphology, radiocarbon dating and genetics. Our results confirm the identification of this specimen as Canis lupus familiaris, discarding miss-identification with a dhole (Cuon alpinus) through genetic analyses of cytochrome b gene and mtDNA haplogroup. The direct AMS 14C dating (17,410–17,096 cal. BP) indicated that the Erralla specimen represents one of the earliest domesticated dogs in Europe, in the Lower Cantabrian Magdalenian period. We discuss our results in the light of the debate of the origin of dogs, conducting a critical review of the datings of sites of Eurasia that have provided remains of Paleolithic and Mesolithic dogs, including the so-called “dog-like wolves”.

14C AMS measurement of gas diluted reactor graphite using a Gas Injection System

For the final disposal of reactor graphite a quantitative characterization of its radioactivity is needed. In this work an emphasis is placed on the isotope 14C, an isotope accessible to AMS measurements. Reactor graphite can be highly activated and therefore difficult to measure without the risk of contaminating the AMS setup. Using an Elemental Analyzer (EA), a Gas Injection System (GIS) and the 6 MV AMS system of the Institute for Nuclear Physics, University of Cologne, we automated the measurement process for gaseous, diluted samples. The presented work shows the first steps to verify the possibility of gas dilution and provides a comparison to samples with known concentrations of 14C. In the future, our system will provide a high sample throughput of gas-diluted probes with high activities.

MARINE RESERVOIR EFFECT OF SPERMACETI, A WAX OBTAINED FROM THE HEAD OF THE SPERM WHALE: A FIRST ESTIMATION FROM MUSEUM SPECIMENS

ABSTRACTSpermaceti is a waxy substance found in the head cavities of sperm whales (Physeter macrocephalus and P. catodon). This substance had a variety of commercial applications from the end of the 18th to the beginning of the 20th century, such as candles, soap, cosmetics and other compounds. Spermaceti was also occasionally used as wax for modeling sculptures. In order to date such artworks the marine reservoir effect (MRE) has to be considered. The chemical library of the Muséum national d’Histoire naturelle (Paris, France) contains samples of spermaceti studied by the French chemist M. E. Chevreul (1786–1889) at the beginning of the 19th century. Eight samples of substances preserved in their original containers were 14C dated. According to the whaling practices and the publications of Chevreul, we estimated that the spermaceti samples came from whales caught between 1805 and 1815. AMS 14C dating results are from 550 to 1180 ± 30 BP, R values between 393 and 1023 (± 34) 14C yr and ΔR between –168 and 504 (± 60) 14C yr. The values presented here are the first ever obtained for spermaceti. However, being based on museum specimens, further measurements on crude material would be necessary to refine these results.

Comparing different machine‐learning techniques to date Nile Delta sediments based on portable X‐ray fluorescence data

AbstractGeomorphology generally aims to describe and investigate the processes that lead to the formation of landscapes, while geochronology is needed to detect their timing and duration. Due to restrictions on exporting geological samples from Egypt, modern geoscientific studies in the Nile Delta lack the possibility of dating the investigated sediments and geological features by standard techniques such as OSL or AMS 14C; therefore, this study aims to validate a new approach using machine‐learning algorithms on portable X‐ray fluorescence (pXRF) data. Archaeologically dated sediments from the archaeological excavations of Buto (Tell el‐Fara'in; on‐site) that pXRF analyses have geochemically characterized serve as training data for running and comparing Neural Nets, Random Forests, and single‐decision trees. The established pXRF fingerprints are transferred via machine‐learning algorithms to set up a chronology for undated sediments from sediment cores (i.e., the test data) of the nearby surroundings (off‐site). Neural Nets and Random Forests work fine in dating sediments and deliver the best classification results compared with single‐decision trees, which struggle with outliers and tend to overfit the training data. Furthermore, Random Forests can be modeled faster and are easier to understand than the complex, less transparent Neural Nets. Therefore, Random Forests provide the best algorithm for studies like this. Furthermore, river features east of Kom el‐Gir are dated to pre‐Ptolemaic times (before 332 B.C.) when Kom el‐Gir had possibly not yet been settled. The research in this paper shows the success of close interactions from various scientific disciplines (Geoinformatics, Physical Geography, Archaeology, Ancient History) to decipher landscape evolution in the long‐term‐settled Nile Delta's environs using machine learning. With the approach's design and the possibility of integrating many other geographical/sedimentological methods, this study demonstrates the potential of the methodological approach to be applied in other geoscientific fields.

Holocene vegetation and climate reconstructions from pollen records in the Mu Us Sandy Land, China

Knowledge of changes in vegetation and climate during the Holocene is important for improved assessments of future climate change and for mitigating climate warming. Owing to the relative difficulty in obtaining high-resolution sedimentary records and identifying pollen, few paleovegetation reconstructions are available from the Mu Us Sandy Land, China. This study analyzes a naturally-exposed fluvio-lacustrine section in the hinterland of the Mu Us Sandy Land. Based on a chronological framework constructed by AMS 14C, a pollen-based random forest model was used to quantitatively reconstruct changes in Holocene climate and normalized difference vegetation index (NDVI) changes. The relationships between NDVI, pollen and precipitation, as well as pollen assemblage characteristics were combined to reconstruct the evolution of the Holocene vegetation in the Mu Us Sandy Land. Our results show that the climate was cold and humid, and the dominant vegetation type was Ephedra shrub-encroached steppe between 11.2 and 8.3 ka BP; the climate reached an optimum, and vegetation evolved into Artemisia–Taraxacum-type–Thalictrum steppe from 8.3 to 2.6 ka BP; and finally, the climate gradually deteriorated and vegetation became an Artemisia–Chenopodiaceae steppe after 2.6 ka BP. In comparisons with other climate records, we found that the Mu Us Sandy Land climate optimum occurred synchronously at 8.3–2.6 ka BP, and the pattern of climate change is closely consistent with the East Asian summer monsoon. We suggest that millennial-scale Holocene climatic change in this region was mainly driven by the influences of high-latitude ice volume and summer solar radiation on the East Asian summer monsoon.

The Vaza-Barris River: A late Quaternary decoupled accumulation-erosion model for rivers of the NE Brazil Atlantic passive margin

Limited insight is available regarding the links between the upstream-downstream fluvial response to climate changes and alluvial-coastal base-level factors in the passive Atlantic margin of tropical South America. This work attempts to characterize the last glacial-interglacial fluvial response of a typical semi-arid Brazilian Northeast River that drains Central-East Brazil's highlands. We integrate the full extension of the Vaza-Barris River alluvial plain record with the alluvial-coastal plain subsurface record. We used digital elevation models, satellite imagery, cores drill description, high-resolution seismic data, optical luminescence, and AMS 14C dating of alluvial terraces Five terrace levels, in the upstream provinces, and three terrace levels in the Coastal-alluvial province were identified. In the continental margin adjacent to the Vaza-Barris river-mouth, incised-valleys in the coastal shelf. Morphosedimentary proxies indicate that periods of aggradation and incision alternated during the late Quaternary due to different inland and eustatic dominant factors. We also estimate that the estuary stored a sediment fill of approximately ∼55 m since the late Pleistocene,. Thus, climate change and sea-level variations differentially controlled the fluvial response and the morphology of the adjacent continental margin along the fluvial system. The decoupled accumulation/erosion upstream-downstream patterns can be used as a model to be tested in fluvial systems of the passive margin of the Brazilian Northeast.

Sedimentary records and chronology of the late Pleistocene overbank flooding in the Yellow River source area, NE Tibetan Plateau

Paleohydrological investigations were carried out in the Yellow River source area on the northeast (NE) Tibetan Plateau. During our fieldwork investigations, two units of overbank flood deposits (OFD) were found in the Maqu-Kesheng reach. These OFD units were studied using a multi-index approach, including magnetic susceptibility, hygroscopic water, grain size distribution and micro-morphological features. It can be inferred that they have recorded two episodes of overbank flooding of the Yellow River. Using the optically stimulated luminescence (OSL) and AMS14C dating techniques, the first episode was dated to 34,680 ± 1880-29000 ± 1790 a and correlated with the late Marine Isotope Stage 3a (MIS 3a) with a warm and wet climate. The second episode occurred at 16,500 ± 1,250-14000 ± 1,280 a, which is coincided with the Bølling-Allerød warm stage during the last deglaciation, a period of coexisting global warming and rapidly shrinking ice sheets. At these two periods, the water was mainly derived from the accelerated melting of mountain glaciers surrounding the basin and/or the large-scale precipitation, which led to the overbank flooding events. At the same time, the related overbank flood deposits were interbedded within glacial outwash/flashflood deposits in the valley bottom of the Yellow River, which intensified the valley aggradation. These results are of great significance in enriching the paleoflood records in the Yellow River source area, recognizing the effect of river system on the development of valley landform, as well as understanding the hydro-climatic response of the Tibetan Plateau to global climate warming occurring presently.

The alteration from agricultural to nomadic regimes resulted in human livelihood transformation in North-Central China during the 12th century: The archaeobotanical evidence.

Human livelihoods provided a crucial economic foundation for social development in ancient times and were influenced by various factors including environmental change, agricultural origin and intensification, as well as long-distance exchange and culinary tradition. The effect of geopolitical change on human subsistence, especially the shifts between agricultural and nomadic regimes, has not been well understood due to the absence of detailed historical records and archaeological evidence. During the 12th century, the control of the Zhengding area in Hebei Province of north-central China changed from the Northern Song (960–1127 CE) to the Jurchen Jin Dynasty (Jin Dynasty; 1115–1234 CE). Recent excavation of the Zhengding Kaiyuan Temple South (ZKS) site in the area provides a rare opportunity to study human livelihood transformation in relation to geopolitical change. In total, 21,588 charred crop caryopses including foxtail millet, wheat, broomcorn millet, hulled barley, and rice, and other carbonized remains including 55.15 g of boiled foxtail millet and 353.5 g of foxtail millet caryopses were identified, and nine AMS 14C dates of crop remains were obtained from the Northern Song and Jin layers at the ZKS site. This revealed that the dominant plant subsistence transformed from wheat to foxtail millet during the change from the Northern Song to the Jin Dynasties in Zhengding area. By comparing with historical documents and paleoclimate records, we propose that this abnormal shift of primary staple food from the relatively high-yield wheat to low-yield foxtail millet was induced by the traditional dietary preference for foxtail millet in the nomadic Jin society. The Jin government levied foxtail millet as taxation and promoted massive immigration from northeastern China to north-central China to consolidate their rule, which resulted in the adoption of foxtail millet as the most important crop in Zhengding area. The advantage for the cultivation of this frost-sensitive crop in north-central China over northeast China was probably enhanced by notable cold events during the 12th century, while the primary influencing factor for the transformation of human livelihoods in north-central China during that period was geopolitics rather than climate change.

Novel use of unique minerals to reveal an intensified methane seep during the last glacial period in the South China Sea

Globally, research aiming to reveal the unique biogeochemical processes and gas hydrate potential in methane seep areas is well established. Furthermore, methane seeps discovered in the South China Sea (SCS) have been widely studied and have achieved significant results. Herein, by systematically analyzing sedimentary samples from the Shenhu area, SCS, we discovered a methane seep that was once active during the last glacial period, particularly the Last Glacial Maximum (LGM) period, and fixed at the seafloor for ∼10 ka. This discovery was achieved by integrating the features of the glauconite within the foraminifera chamber, different morphologies of pyrites, and unique framboid goethites (pyrite pseudomorphs). In addition, this study accounted for the high chromium-reducible sulfur content and extremely negative δ34S values (from −50.78 to −46.92%) between 121 and 231 cmbsf, the Mo content and its correlation with total sulfur (TS) and total organic carbon (TOC), the TS/TOC ratios of sediments, the results of AMS 14C dating, and the results of planktonic foraminifera analysis in the case of carbon and oxygen isotopes. Glauconite, which is usually considered a product associated with transgressive deposits and condensed sections, is widely found in warm climatic intervals. However, these intervals are generally associated with methane emission events. Thus, our results demonstrate another mechanism for the formation of glauconite in methane seeps during the LGM. Furthermore, the existence of framboid goethites implies that this methane seep has been subsiding since the end of the LGM and that few pyrites that formed previously were reoxidized. Notably, this study is the first to report a systematic investigation of methane seep activity during the last glacial period by the indication of authigenic minerals, such as glauconite and framboid goethite, in the SCS. Overall, our results show a direct relationship between methane seep activity and climatic variation.

Sedimentary records of mid-Holocene extreme storm events on the north bank of Hangzhou Bay, East China

Reconstructing the long-term history of tropical cyclones is key to understanding their driving mechanisms and to enable better predictions of future extreme storm events. However, the available history of typhoons, based on sedimentary records in the northwest Pacific basin, remains very limited. In this study, we conducted multi-proxy analyses of sedimentary profiles collected from a chenier ridge on the north bank of Hangzhou Bay, East China. We applied evidences from the lithology, grain size, and marine micro-fossils on sediments in these profiles, dated using OSL and AMS 14C, to reveal the mid-Holocene sedimentary environmental evolution and obtain records of extreme storm events. The lithology and foraminiferal assemblages indicate an aggradational succession from intertidal to supratidal flats incorporating two layers of storm deposits preserved in the chenier ridge. The lower layer of storm deposits was formed in the intertidal flats at ca. 6.0 cal. kyr BP, while the upper layer was formed in the supratidal flats at ca. 5.2–4.9 cal. kyr BP. The storm deposits are characterized by coarsened grain size and the prevalence of allochthonous foraminiferal species, including E. advenum, A. annectens, and A. compressiuscula which occur in the inner and middle shelf of East China Sea. The extreme storm events at ca. 6.0 and 5.2–4.9 cal. kyr BP recorded at the chenier ridge have also been described at different sites on the southeast coast of Hangzhou Bay. Together with previously reported storm deposits at ca. 4.5 cal. kyr BP, we suggest that these mid-Holocene extreme typhoon events on the East China coast resulted from global climate changes driven by solar irradiance.

Environmental reconstruction and formation processes in a large Mesolithic lithic scatter at Nethermills of Crathes, Aberdeenshire, Scotland

The rich resources of river valleys provided a focus for much Mesolithic hunter-gatherer-fisher activities across Europe. In Scotland there is one notable concentration of lithic evidence for this, at several locations along the River Dee in Aberdeenshire, but the environmental context of these sites has, to date, been poorly understood. Here we present evidence from excavation, repeated field-walking, flint typology, geomorphological mapping, sedimentology, pollen analysis, AMS 14C dating, OSL profiling and dating to understand the postglacial evolution of the terrace surface at the largest concentration of lithics along the River Dee, at Nethermills of Crathes. The aim was to understand in detail the environment and landscape dynamics of the site, to define whether occupation was on the active valley floor or on a terrace above the river, and whether fluvial processes had a role in site formation processes. We conclude that occupation was on a dry wooded surface, the active channel having incised below this, though to an unknown depth, and that although major floods have swept the terrace surface, the present distribution of lithics is probably largely the original distribution.

Paleochannel of the Yellow River within the Zoige Basin and its environmental significance on the NE Tibetan Plateau

Paleochannel sedimentary sequences can provide abundant information on regional environmental changes. A typical paleochannel (paleo-oxbow lake type) section of the Yellow River was identified within the Zoige Basin on the NE Tibetan Plateau. A multi-index approach was used to accurately identify sediments of different genetic types, such as riverbed deposits of the Yellow River, paleo-oxbow lake deposits, and overbank flood deposits (OFD) in the section. Based on optically stimulated luminescence (OSL) and AMS 14C dates, we examined the environmental evolution recorded by the section. The results show that: (1) The section is a record of environmental change since 4.17 ± 0.49 ka. During 4.17 ± 0.49 to 3.24 ± 0.26 ka, the ancient Yellow River occupied the channel. At 3.24 ± 0.26 ka, the paleochannel experienced a neck cutoff, and the fluvial environment began to change into the oxbow lake environment. After 2.45 ± 0.11 ka, the paleo-oxbow lake gradually disappeared. Subalpine meadow soil has developed at this site since 1.31 ± 0.05 ka. (2) Paleoenvironmental proxies indicate that the Zoige Basin was warmer and wetter before ~3.00 ka, and became drier and colder after ~3.00 ka, which may be mainly related to the weakening of the East Asian summer monsoon (EASM) and the strengthening of the Westerlies. (3) Two episodes of extreme overbank flooding occurred at 2.96 ± 0.24 to 2.87 ± 0.27 ka and 1.84 ± 0.20 to 1.70 ± 0.16 ka, correlated with climate shift period from the mid-Holocene climatic optimum to the late Holocene and the Dark Age Cold Period (DACP), respectively. Due to the relatively cold and dry climate in these periods, glaciers generally advanced on the Tibetan Plateau, and the contribution of snow and ice meltwater weakened. Therefore, the strong rainfall caused by the abnormal atmospheric circulation may be the main cause of these extreme overbank flooding.

Chronology of Last Glacial Maximum sediments in the coast of Fujian, South China

The coast in South China is an important area for the coupling of terrestrial, marine, and atmospheric processes. Widespread loose sediments in the area likely recorded regional climatic and geomorphic processes since the Late Pleistocene, and these that can be deciphered through geochronology. In the present study, eighteen samples prepared from the FN1 core retrieved from the Funing Bay in the coast of Fujian were used for OSL dating. The single-aliquot regenerative-dose (SAR) approach was employed for dating using three grain-size fractions of quartz, while coarse-grained K-feldspars were used for post-infrared infrared stimulated luminescence (pIRIR) dating of the core. Seven samples were also dated using the AMS 14C dating technique to establish the reliable chronology. The results reveal the following: 1) Minerals and grain size variations directly affect the accuracy of the luminescence dating. The present study demonstrates that cross-validation of the OSL dating data is an effective way to enhance their reliability. 2) Dating results from the three grain-size fractions of quartz in the upper section of the core are consistent within the error range, and these agree with ages from the AMS 14C method for the corresponding horizon. However, the OSL ages based on the three grain-size fractions of quartz and the coarse-grain K-feldspar differed for the lower section of the core (10.6–14.7 m). 3) Samples produced ages ranging from 25.4 to 0.8 ka based on the OSL dating method. According to a chronological framework starting from the Last Glacial Maximum and a palaeoenvironmental index, the sedimentation rate is partitioned into three main periods. Sedimentation rates during the periods between 25 and 21 ka and < 7 ka are higher than those for the period between 21 and 7 ka. These results suggest that the sedimentation rate was probably linked to the regional transgression events.

Moisture conditions during the Younger Dryas and 4.2 ka event as revealed from a subalpine peat record in the Luoxiao Mountains, southern China

A 150 cm long peat core was collected from a subalpine peatland (above sea level 1790 m) in Luoxiao Mountains，Hunan Province, China. Based on the analysis of AMS 14C dating, loss on ignition, total carbon, total nitrogen, grain size, humification, and pollen data, the environment change was reconstructed focusing on the intervals of the Younger Dryas (YD) event, the 4.2 ka event, and modern time. The pollen record indicates that deciduous broad-leaved trees occupied most parts of the study region and subtropical trees also grew at the lower elevation areas during the deglaciation. The percentages of Quercus (D) reached the highest during the YD, suggesting lowered temperatures than that of the pre-YD. Comparing with modern pollen assemblages, the relative abundance of Tsuga was lower during the 4.2 ka event, suggesting that the temperature were lower than that of the present. Regional comparisons of multiple proxy data in eastern China revealed that the climate was wet in northern China during the YD, which was probably related to the weakening evaporation effect and the strengthening Okhotsk High under low-temperature conditions. During the YD, the climate in the area dominated by the Indian monsoon was relatively dry in the southern part of eastern China. Meanwhile, in the East Asian monsoon-affected region, the climate was relatively wet during the YD in the southern part of eastern China, which was related to the weakening of the East Asian monsoon, El Niño conditions, and the West Pacific Subtropical High.

Multi‐Centennial Variability of Yangtze Delta Growth Over the Last 2000 Years: Interplay of Climate and People

AbstractReconstruction of sediment accumulation in river deltas over the Holocene provides a basis for understanding the relationship between climate change, human activities and delta growth. However, variations in deposition rates on a centennial‐scale over the last 2000 years remain poorly studied for mega‐deltas. Based on optically stimulated luminescence and AMS 14C ages, we calculated deposited sediment volumes in the Yangtze River Delta (YRD) for 500‐year intervals over the last two millennia for the first time. Our results reveal that the 2.0–1.5 and 0.5–0 ka periods had higher sediment deposition rates than in 1.5–1.0 and 1.0–0.5 ka, with maximum value about two times that of the minimum. A comparison with historical records of flooding and drought events indicates that a wetter climate led to a higher sediment deposition, reflecting the role of fluvial discharge in delta growth. However, the highest sediment deposition (205 ± 29 × 106 m3/a) over the last 500 years is not only related to the wetter conditions of the Little Ice Age, but also linked to dramatic regional population growth. We suggest that human activities have predominated over natural forcing in determining the deltaic growth over the last five centuries. Taking the Medieval Climate Anomaly with the lowest deposition volume as an analog of current climate warming, and considering the decline in sediment loads due to recent damming and soil conservation, the YRD is likely to face an even more severe deficit in sediment supply and higher risk of delta destruction in the coming centuries.

Interannual Variations of D14CTOC and Elemental Contents in the Laminated Sediments of the Santa Barbara Basin During the Past 200 Years

A 51-cm core (SBB-8-2012) from the depo-center of Santa Barbara Basin (SBB), California has been dated by 210Pb dating and varve counting, spanning a depositional history during 1815-2011 CE. A total of 89 AMS 14C measurements on samples from 66 horizons, including animal cartilage, shell and total organic carbon (TOC) in the sediments show apparent 14C ages between 500 and 4000 yr BP. Among these AMS dates, D14C values measured in 78 samples from 62 horizons vary in the range of -64.3‰ to -383.8‰. The 14CTOC ages much older than predicted from our sedimentation model are influenced by the input of terrigenous sediments, changes in ocean circulation, biological input and carbon remineralization. Three strong old 14CTOC excursions at 1964~69, 1884~87 and 1819~21 CE indicate higher old carbon input caused by some unusual events (e.g., oil spill, flood event and earthquake). On multi-decadal timescales, the D14CTOC shifts in three zones were mainly caused by changes in fossil carbon emission from the seafloor, fraction of marine productivity to terrigenous input of organic carbon (OC) and the atmospheric nuclear bomb testing input of 14C into the SBB. On interannual to decadal timescales, variations of D14CTOC correspond to El Niño-Southern Oscillation effects. During the La Niña period, stronger upwelling and northerly California Current bring nutrient-enriched water into SBB and lead to higher productivity hence more marine OC with higher D14CTOC. In addition, reduced terrigenous input of OC with lower D14C under less coastal rainfall during La Niña could further elevate the D14CTOC. Lower scanning XRF (K+Ti)/2 (indicating lower terrigenous input), higher scanning XRF Sr/Ti as well as acid-leachable elements (reflecting higher biogenic components), and higher D14CTOC occur during La Niña. During the El Niño period, the phenomena are opposite. Spectrum analyses of the Southern Oscillation Index (SOI) and the D14CTOC as well as the comparison of SOI and SBB-8-2012 records support our scenarios.

NEW CHRONOLOGY FOR MEGALITHIC BURIALS IN VIDARBHA (CENTRAL INDIA): INSIGHTS INTO CONTEMPORARY HYDRO-CLIMATE AND FOOD HABITS

ABSTRACTMegalithic cultures of central India provide important links between the southern Neolithic-Chalcolithic cultures and the early Historical period (∼500 BC to ∼AD 700) and reveal knowledge of ancient traditions of early inhabitants. Scientific dating of these Megalithic burial sites is a challenging task due to scarcity of dateable material and alterations. Here, we present multiple accelerator mass spectrometry radiocarbon (AMS 14C) dates from equine tooth-enamel and organic food remains recovered from pots from Megalithic burials of the Vidarbha region. Using δ13CTOC and δ15N values of organic food remains recovered from pots, we deduced past-diet (palaeo-vegetation) that indicates C4 type of vegetation and thus arid climate during life-spans of these burials. We also analyzed stable δ13C and δ18O isotopes of equine tooth-enamel to investigate hydro-climatic conditions of Maharashtra (Vidarbha region). A total of 10 AMS 14C dates of tooth enamel provide a time range of AD 250–874 for two Megalithic burials. Two AMS 14C dates of organic food remains recovered from pots corroborated aforementioned time-range. The average δ13C and δ18O of equine tooth-enamel samples were −5.3 ± 2.1‰ and −2.9 ± 0.8‰, respectively, both significantly enriched compared to their modern counterparts (−13.7‰ ± 0.7 and −4.3‰ ± 1.1), indicating intense arid conditions in the past.