Accelerator Mass Spectrometry 14C Dating Research Articles

Quantitative reconstruction of precipitation changes in the Mongolian Altai Mountains since 13.7 ka

Holocene climate changes in the Altai Mountains and the surrounding areas are well documented, but the timing of the Holocene precipitation maximum remains controversial. We obtained 17 accelerator mass spectrometry (AMS) 14C dates and 310 fossil pollen assemblages from sediments in Tolbo Lake, which we used to reconstruct the history of vegetation and climate change in the Mongolian Altai Mountains over the past 13,750 years. The results suggest that mean annual precipitation (Pann) was the most significant control on the fossil pollen record at the study site. Based on the fossil pollen record from Tolbo Lake and 469 surface pollen samples within the radius of 1300 km, the reconstructed Pann was lowest during 13.7–11.3 ka (1 ka = 1,000 cal yr BP); relatively low but increasing Pann occurred in the early Holocene (11.3–9.4 ka); and maximum Pann occurred during the middle to late Holocene (after 6.8 ka), possibly because of the high temperatures. A significant climatic and ecological transition occurred in the Altai Mountains at ∼7 ka: steppe and desert steppe vegetation with generally low Pann was present before ∼7 ka, while subsequently there was the expansion of forest vegetation and a marked increase in Pann, possibly in response to the minimum in Northern Hemisphere ice sheets and the increased radiative forcing caused by rising atmospheric greenhouse gases.

Holocene evolution of the Banni Plain at the north‐east margin of the Arabian Sea: Constraints from a ca 50 m long sediment core

AbstractHolocene evolutionary history of the Banni Plain in the Great Rann of the Kachchh Basin is reconstructed from a subsurface sediment core of ca 50 m. Detailed data on textural and lithofacies variations, grain‐size analysis, environmental magnetism and accelerator mass spectrometry 14C dates on seven samples were generated on the sediment core retrieved from the Banni Plain near Berada. A high‐resolution record extending back to 10 ka has been reconstructed from the top ca 40 m of the core section comprising shallow marine sediments. The core is divisible into five depositional units. The basal part is a fluvial depositional unit followed upward by estuarine, sub‐tidal, intertidal and supra‐tidal environments. The sediment accumulation rate is highest in the sub‐tidal to intertidal facies (1.9 cm year−1) and decreases towards the supra‐tidal facies to 0.09 cm year−1. Environmental magnetic analysis, χlf coupled with the S‐ratio, indicates high magnetic mineral concentrations during the Early Holocene, suggesting a wet period accompanied by high monsoon precipitation. This is followed by the onset of semi‐arid conditions in the Great Rann of the Kachchh Basin as indicated by the low values of the χlf and S‐ratios. A westward and northward shift in the shoreline towards the deeper part of the basin is suggested during the Late Holocene, which is coupled with aridity and reduced monsoonal conditions. The change in depositional pattern from the retrogradational deposit of fluvial (Unit 1) to estuarine sediment (Unit 2), progressing to sub‐tidal (Unit 3), is attributed to sea‐level transgression followed by regressive intertidal (Unit 4) to supra‐tidal deposition (Unit 5), culminating in complete withdrawal of the sea, aided by tectonic uplift, during the Late Holocene. The results reveal that the sediment accumulation rates and depositional environments changed over time in response to changes in sea level from minima to maxima and then eventually to the present level.

Late Pleistocene boreal molluscs in the Gulf of Cadiz: Past and current oceanographic implications

Remains of molluscs were collected from the seafloor on the north-eastern margin of the Gulf of Cadiz, between 300 and 1000 m water depth, using different sampling methods (e.g. dredging, trawling and box-coring), during several deep-sea expeditions. Samples contained a suite of species which nowadays mostly occur northwards of the English Channel, together with other widespread species. Species now locally extinct in the Gulf of Cadiz and restricted to northern latitudes, which unequivocally indicate a faunal shift, include the gastropods Buccinum undatum, Colus gracilis, Liomesus ovum and Neptunea antiqua, the bivalves Arctica islandica, Chlamys islandica, Modiolus modiolus, Mya truncata and Nuculana pernula and the scaphopod Antalis entalis. These species represent “Boreal Guests” of marked palaeoclimatic significance, some of which are reported for the first time in the Gulf of Cadiz. The boreal species collected were mostly large (>5 cm) whereas smaller boreal species were extremely scarce, probably winnowed away by strong bottom currents. The pteropod Limacina retroversa, at present restricted to water masses northwards of the Iberian Peninsula but widespread in Mediterranean sediments of the last glaciation, was also recorded. Accelerator mass spectrometry (AMS) 14C dates obtained from nine specimens of molluscs ranged between 26.1 and 14.6 kyr B.P., thus confirming their attribution to a last glacial assemblage. The abundance of these molluscan remains in the present Mediterranean Outflow Water pathway could be explained if this outflow was reduced in intensity or more likely shifted to a deeper level, leaving the upper slope in contact with suitable Atlantic intermediate waters. The findings of Boreal Guests in the Gulf of Cadiz document the continuity of the faunal shift which is well-known in the Mediterranean basin. Species still living in the Gulf of Cadiz and the Alboran Sea nevertheless account for 84.6% of specimens among the larger species.

Non-climate environmental factors matter to Holocene dynamics of soil organic carbon and nitrogen in an alpine permafrost wetland, Qinghai‒Tibet Plateau

Studies on the responses of soil organic carbon (SOC) and nitrogen dynamics to Holocene climate and environment in permafrost peatlands and/or wetlands might serve as analogues for future scenarios, and they can help predict the fate of the frozen SOC and nitrogen under a warming climate. To date, little is known about these issues on the Qinghai‒Tibet Plateau (QTP). Here, we investigated the accumulations of SOC and nitrogen in a permafrost wetland on the northeastern QTP, and analyzed their links with Holocene climatic and environmental changes. In order to do so, we studied grain size, soil organic matter, SOC, and nitrogen contents, bulk density, geochemical parameters, and the accelerator mass spectrometry (AMS) 14C dating of the 216-cm-deep wetland profile. SOC and nitrogen contents revealed a general uptrend over last 7300 years. SOC stocks for depths of 0–100 and 0–200 cm were 50.1 and 79.0 kgC m−2, respectively, and nitrogen stocks for the same depths were 4.3 and 6.6 kgN m−2, respectively. Overall, a cooling and drying trend for regional climate over last 7300 years was inferred from the declining chemical weathering and humidity index. Meanwhile, SOC and nitrogen accumulated rapidly in 1110–720 BP, while apparent accumulation rates of SOC and nitrogen were much lower during the other periods of the last 7300 years. Consequently, we proposed a probable conceptual framework for the concordant development of syngenetic permafrost and SOC and nitrogen accumulations in alpine permafrost wetlands. This indicates that, apart from controls of climate, non-climate environmental factors, such as dust deposition and site hydrology, matter to SOC and nitrogen accumulations in permafrost wetlands. We emphasized that environmental changes driven by climate change have important impacts on SOC and nitrogen accumulations in alpine permafrost wetlands. This study could provide data support for regional and global estimates of SOC and nitrogen pools and for global models on carbon‒climate interactions that take into account of alpine permafrost wetlands on the northeastern QTP at mid-latitudes.

Holocene Paleoenvironmental Implications of Diatom, Non-Pollen Palynomorph, and Organic Carbon Records from the Kandalaksha Bay of the White Sea (European Arctic)

Variations in sea surface conditions and sea level through the Holocene in the Kandalaksha Bay, the White Sea, were reconstructed based on the study of core sediments from the outer Kandalaksha Bay, using the modern analog technique applied to dinocysts in addition to diatoms, TOC, δ13Corg, CaCO3, and grain size data. The chronostratigraphy of the core sediments was defined from accelerator mass spectrometry 14C dates on mollusk shells. The results indicated an increase in water depth in the outer Kandalaksha Bay and in the central Dvina Bay until the late Holocene. From about 9.5 to 7.5 cal kyr BP, the data suggested a general trend of increasing sea surface temperatures (up to 14 °C), at least in areas with inflow of Atlantic waters. The last 2.5 kyr were characterized by increased freshwater runoff to the White Sea.

Sedimental pollen records in the northern South China Sea and their paleoenvironmental significance

Studies on the reconstruction of long-term climatic and vegetation dynamics around the northern South China Sea (SCS) are limited. Therefore, this study was conducted to get a clear understanding of the paleoenvironmental significance around the Taiwan Strait in northern SCS. The chronology was based on the accelerator mass spectrometry (AMS) 14C dates of mixed planktonic foraminifera, then we compared and cross-validated the age–depth model based on the grain-size analysis and foraminifera data. Palynomorph data, including percentages and concentrations based on marine sediment cores (WQZK1, WQZK2, and WQZK3), were used to reconstruct the history of vegetation and climate changes and identify the provenance and transport mechanisms of pollen and spores. The findings indicated that fern spores dominated the interglacial period, suggesting intense summer monsoons during warm periods in marine isotope stages (MIS) 5–MIS 1. During MIS 5a, tropical and subtropical conifers with temperate components dominated, indicating the climate was comparatively warm at an increasing sea level. The lowest sea level subtly proved cooler and wetter climate, subsequently affecting a drastic increase of Pinus during MIS 4. Tropical and subtropical conifers dominated during the MIS 3, and the sea level increased comparatively to MIS 4, indicating warmer climate conditions. Pinus pollen and fern spores dominated MIS 1, implying that the paleoenvironment was comparable to the present day. Therefore, this study supports previous studies on the northern SCS region and suggests that a combination of pollen with other proxies provides a better understanding of vegetation and climatic dynamics in the past.

Bioturbation supplying young carbon into West Antarctic continental margin sediment

Accelerator Mass Spectrometry (AMS) 14C dating is a widely applied method for establishing high-precision chronologies used to underpin late Quaternary paleoclimatic studies. Feedbacks associated with Antarctic Ice Sheets (AIS) and Southern Ocean variance are thought to have played a critical role in regulating past global climate changes since the Last Glacial Maximum. However, determining the exact role of the AIS and Southern Ocean in these changes has proven difficult because of the sparse occurrence of biogenic carbonate suitable for AMS 14C dating in Antarctica. Consequently, AMS 14C dating is often measured on acid insoluble organic matter (AIOM) from bulk sediment samples, which are often biased towards ages that are older than the depositional age, due to pervasive reworking of old carbon. In this scenario, ages can still potentially provide maximum deposition ages, but such interpretations need to be assessed carefully. Here, we document AIOM and foraminifer AMS 14C dates at the same depth intervals from Antarctic continental margin cores, and we find AIOM AMS 14C dates can range between 2000 and 16,000 years younger than those of foraminifera samples. The younger AIOM 14C dates were found in bioturbated sedimentary facies, which often have extremely low sedimentation rates in Antarctica. In cores with low sedimentation rates, the down sediment contribution of organic carbon from macro-benthos can be quite significant in the sediment column with low organic carbon concentration. After considering possibilities of contamination, foraminifer reworking, and remineralization of secondary carbonate to explain this offset, we conclude that bioturbation plays an important role in the Antarctic carbon cycle as a young carbon supplier to depth into the sediment column. This has clear implications for using condensed sedimentary sections to date post-LGM records in Antarctica. These bioturbation processes also have implications for novel radiocarbon dating methods that have recently been developed to overcome sediment reworking processes and more accurately constrain timing of past AIS retreat, including ramped pyrolysis and compound specific isotopes methods.

Contourite systems around the northern exit from the Vema Channel

Several drifts of different types and sizes are identified near the northern exit of the Vema Channel, within the projects Neogene-Quaternary contourites of the Central and South Atlantic and Lateral sedimentation in the deep ocean (on the examples from the Central and South-Western Atlantic). Herein, we discuss new results of a multidisciplinary study of sixteen sediment cores and high-resolution sub-bottom (seismoacoustic) profiles, to address the impact of Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW) passing through the Vema gateway on contourite accumulation and erosion. To the west of the northern exit from the Vema Channel, an anticyclonic gyre of LCDW is instrumental in the development of contourite drifts and sediment waves. The contourite origin of generally silty terrigenous sediments in the Santa Catarina Plateau – São Paulo Plateau area is ascertained by both morpho-seismic and sedimentary characteristics. Sedimentary features include: a lack of primary sedimentary structures and pervasive bioturbation; sharp erosional contacts, local hiatuses and stiff mud horizons; some sandy/silty layers and indistinct bedding; mostly fine grain-size, very poor sorting and distinctive bi-gradational sequences; a high degree of correlation between the content of sortable silt (SS) in the total < 63 μm size fraction and SS mean sizes in all eight cores studied. Biostratigraphy, oxygen isotope records and ten new accelerator mass-spectrometry (AMS) 14C dates reveal the mid to late Quaternary age of this mainly terrigenous contourite depositional system (CDS).By contrast, the dominantly calcareous Ioffe Drift, overlying the Florianopolis Fracture Zone (FFZ) ridge to the northeast of the Vema Channel, is far from any source of terrigenous material, and accumulated in an area of low biological productivity. The overall asymmetric geometry, mainly lenticular, upward-convex seismic units separated by erosional unconformities, reflection truncation, small-scale moats dissecting the drift surface collectively indicate its contourite origin. The interpretation of the drift as the CDS is supported by sediment characteristics including common hiatuses corresponding in some cases to erosional contacts, pervasive bioturbation, generally poor sediment sorting, and more or less well-developed bi-gradational sequences. The erosion and deposition in the drift area are mostly controlled by the main LCDW branch following northeastward along the FFZ. Extensive erosion by bottom currents has created numerous hiatuses and markedly reduced the thickness of drift's sediments. The stratigraphic record from the Ioffe Drift sediment cores reveals an Upper Pliocene – Quaternary succession. The results of detailed analyses of six cores from the Ioffe Drift area, compared with two cores and the upper part of DSDP Site 516 from the Rio Grande Rise, notably the use of a SS analogue, provide new information on calcareous biogenic contourites deposited in the pelagic realm of the South Atlantic.

Late Holocene hydroclimatic changes inferred from a karst peat archive in the western Guizhou Plateau, SW China

The paleoenvironmental implications of Ca-related indices of peat from karst regions are poorly understood. In this study, we analyze a 450-cm peat core drilled from a sub-alpine karst mountain in the western Guizhou Plateau, SW China. This core is analyzed for carbonate contents and loss on ignition (LOI). High-resolution X-ray fluorescence (XRF) core scanning was also performed to see the variation of chemical compositions. Based on these measurements and 12 accelerator mass spectrometry (AMS)14C dates, we reconstructed the history of hydroclimatic shifts in SW China and explored the significance of Ca-related indices. The reconstructed hydroclimatic conditions were consistent with the stalagmite, lacustrine sediment, and peat records from the regions controlled by the Indian monsoon. Abrupt decreases in precipitation and temperature were clearly shown during the 4.2 ka and Little Ice Age (LIA) cold events. High carbonate contents in the Yejiping peat during the Medieval Warm Period (MWP) were linked to a warm and humid climate. Additionally, wavelet analysis shows that variations in Ca content have 500, 125, 103, 80, 58, 43, 20, and 12-a quasi-periods, which correspond to the Gleissberg, Pacific Decadal Oscillation (PDO), and Schwabe cycles. Our results highlight the importance of Ca-related indices in peat deposits from karst depressions and provide a detailed description of the MWP and the LIA.

The Holocene paleoenvironmental history of Western Caucasus (Russia) reconstructed by multi-proxy analysis of the continuous sediment sequence from Lake Khuko

This paper presents new multi-proxy records of the Holocene environmental and climatic changes in the Western Caucasus revealed from a continuous sediment sequence from mountainous Lake Khuko (Caucasus State Natural Biospheric Reserve, 1744 m a.s.l.). Palaeoecological analyses of a sediment core for grain size, magnetic susceptibility, loss on ignition, and pollen allowed us to determine five principal climatic phases with several subphases since 10.5 ka BP. The age model is based on seven accelerator mass spectrometry 14C dates, supplemented by 210Pb data for the uppermost part of the sediment core. Warm periods (10.5–6.7, 6.7–5.5, 3.5–2.4, 0.8–0.5 ka BP) were characterized by high biological productivity in the lake as indicated by high organic matter content and expansion of forests, typical of modern low and middle mountain zones, as indicated by the increase in abundance of Quercus, Ulmus, Corylus, and Tilia in the pollen assemblages. Cold periods (5.5–3.5, 2.4–0.8, and 0.5 ka BP–present) are marked by a consistent decrease in organic matter content in lake deposits and possibly higher intensity of the catchment erosion. The changes in pollen assemblages (for instance peaks of Abies, Picea, and Pinus) suggested a potential elevational decline in the boundaries of vegetation belts and expansion of high-altitude woodlands. Abrupt changes in the lake ecosystem were identified between 4.2 and 3.5 ka cal BP marked by a short-term variation in sediment regime shown by variation in organic matter content, magnetic susceptibility values, and sediment grain size. This was probably caused by climatic fluctuations in the Western Caucasus region as a result of complex shifts in the ocean-atmosphere system during the 4.2 ka event. Overall, the first Holocene multi-proxy continuous lake sediment record provides new insights into the climate history in the Western Caucasus.

Landscape evolution in the Liangzhu area since the early Holocene: A comprehensive sedimentological approach

The Liangzhu culture (5300– 4300 cal yr BP) is considered to be the testification of the five thousand year history of Chinese civilization, and has thus attracted a great deal of attention from the archaeological community. However, the rise and fall of the Liangzhu culture, especially the cause of its vanishing, is still a topic of intense debate. Since the Liangzhu Ancient City area is a low-lying littoral region with a dense network of waterways, the landscape evolution would have had great impact on human-environment interactions. In this study, we will reconstruct the evolutionary history of the landscape by using sedimentological approach. Five sediment cores, together with trenches exposed in the archaeological sites were investigated. The chronology of the sediments was established by using twelve accelerator mass spectrometry (AMS) 14C dates. Sedimentary proxies, including calcium content, grain size, diatoms, and dinoflagellates are used for paleoenvironmental reconstruction. The results showed that: (1) from the last deglaciation to the early Holocene (before ca. 9400 cal yr BP), the Liangzhu area was widely exposed, and the cores contain coarse sand, gravel, and hard clay layers; (2) during the early to middle Holocene (ca. 9400 – 7600 cal yr BP), the area was rapidly submerged by a westward marine transgression, and the subsequent marine regression moved eastward from the Liangzhu area at approximately 7900 – 7600 cal yr BP when the rate of sediment supply exceeded the rate of relative sea level (RSL) rise; (3) during the middle to late Holocene (after ca. 7600 cal yr BP), the deposits mainly originated from overbank flooding or from storm surge events rather than from direct RSL rise from ca. 7600 – 6600 cal yr BP. The Liangzhu Ancient City area remained a swamp and an area of salinization until ca. 5100 cal yr BP.

The diatom response to Postglacial environments in the White Sea, the European Arctic

The White Sea is a small semi-enclosed Arctic sea influenced by Atlantic waters. It was completely covered by the Scandinavian Ice Sheet in the Late Pleistocene and plays a key role in the reconstruction of the degradation of the Scandinavian Ice Sheet and Atlantic Water advection into the Arctic Ocean. We examined the inflow of Atlantic water into the White Sea Basin as the leading feature of postglacial sedimentation processes. Palaeoreconstructions were conducted through detailed studies of diatom assemblages in two sediment cores from the central area (PS-6042) and outer part (PS-6050) of Dvina Bay. Stratigraphic division of the core sediments was performed on the basis of palynostratigraphy and accelerator mass spectrometry 14C dates. The composition of diatom assemblages in postglacial sediments from Dvina Bay indicate a change in the environment from a freshwater sea bay to fully marine conditions over the past 12 cal kyr. Based on the obtained results, we established that the Atlantic water started to flow into the central Dvina Bay in the first half of the Preboreal (11.7–11.3 cal ka BP), and the greatest increase in water surface temperatures in central Dvina Bay occurred during the period from the end of the Atlantic to the first half of the Subboreal. We confirmed these conclusions through comparison with previously obtained results of aquatic palynomorphs, pollen and spores, grain size analysis, and measurements of total organic carbon and biogenic silica contents, as well as through correlation with published palaeoreconstructions of the White Sea and the Arctic Ocean.

Holocene sedimentary evolution and hypoxia development in the subaqueous Yangtze (Changjiang) Delta, China

This study investigates Holocene sedimentary evolution and hypoxia development using borehole cores CJK06 and CJK09, in combination with other published core data. Based on lithology and microfossil (benthic foraminifera) characteristics, seven types of sedimentary facies were identified from the base upward: river, tidal flat, tide-influenced river, transgressive lag, estuary, inner-shelf, and prodelta. Isochronous correlation among the cores was established relying on accelerator mass spectrometry 14C dates. Facies succession indicates that a weak progradation occurred in coastal environments (12–10 ka BP) due to the Younger Dryas-induced deceleration of sea-level rise; rapid deposition locally occurred in the southern marginal area of tide-dominated estuary environments (10–8 ka BP), likely due to the junction of the Yangtze and Qiantangjiang River currents; and marine current-induced fluid mudflows prevailed in the shallow marine environments (8–1 ka BP), with the cooling climates of 5–1 ka BP. Furthermore, prodelta and shallow marine environments co-occurred with an uneven progradation of the delta within the last 1 ka, while deposition occurred just inside the more southern, delta-influenced area. The occurrence of euryhaline benthic foraminifera suggests that an enhanced freshwater discharge of the mid-Holocene (8–5 ka BP) was followed by a sharp decline in the late Holocene (5–1 ka BP) with climate change. The occurrence of cold-water benthic foraminifera indicates a severe cold-water condition during the mid-Holocene due to the intrusion of upwelling currents triggered by the propelling force of warm currents and summer monsoon winds. In addition, the occurrence of low-oxygen foraminiferal assemblages reveals that hypoxia has developed since 10 ka BP in stages consistent with the sedimentary evolution: localized hypoxia formation coincident with the southern depocenter during the early Holocene (10–8 ka BP); severe hypoxia with enhanced freshwater discharge and upwelling current intrusion during the mid-Holocene; and weakened hypoxia of the late Holocene, mainly due to the sharp decline in freshwater discharge. Within 1 ka BP, freshwater discharge from the approaching river mouth and increased nutrient inputs from enhanced human activities on land have contributed to the prevalence of hypoxia, especially in the southern deltaic area. Overall, it was revealed that the freshwater discharge modulated with climate variations and delta progradation plays a primary role in controlling the sedimentary evolution and hypoxia development during the mid-late Holocene.

Winter-to-summer seasonal migration of microlithic human activities on the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau (QTP) has become a valuable site for investigation of adaptive regimes of prehistoric humans to extreme environments. At present most studies have focused solely on a single site. Using a more integrated approach that covers the complete scope of the plateau is needed to better understand the expansion logic of prehistoric humans moving towards the plateau. Here, we conducted accelerator mass spectrometry 14C dating of two microlithic sites. Canxiongashuo (CXGS) and Shalongka (SLK), which are located at the inner and marginal areas of the QTP, respectively. By using geographic information system, literature, and natural environmental factors, we constructed a model for the relationship between traveling distance and time, and we also used these factors to construct a plateau environmental index. The results indicated that the ages of the CXGS and SLK sites are 8.4–7.5 cal. ka BP and 8.4–6.2 cal. ka BP, respectively. Combining the archaeological evidence and literature, hunter-gatherers may have seasonal migration activities at low altitude in winter and high altitude in summer in order to make full use of natural resources. Our model of relationship between traveling distance and time shows that hunter-gatherers in CXGS site was active on the plateau all year-round at approximately 8.3 cal. ka BP. According to EI and archaeological remains, we propose that SLK site was a winter camp of prehistoric hunter-gatherers. Taken together, we determined 8.4–6.0 cal. ka BP as a transitional period from the Paleolithic to Neolithic Ages, and winter camps of hunter-gatherers evolved into settlements in the Neolithic Age.

CHRONOLOGY OF THE ARCHAEOLOGICAL SITE OF PLAYA DEL MANGO, RIO CAUTO, GRANMA, CUBA

ABSTRACTFewer than 200 radiocarbon (14C) dates with secure contextual information are available for Cuba, making it challenging to reconstruct Caribbean indigenous population dynamics, their identities and interactions. In this paper, we discussed 21 accelerator mass spectrometry (AMS) 14C dates from two mounds (M1 and M2) at the Playa del Mango site (Granma province, Cuba), traditionally associated with the Banwaroid stone tool tradition. The ΔR calculated for the site was –132.0 ± 176 and –164.0 ± 68. The chronology of burials from the peripheral area of M2 suggested that the cemetery was continuously used from at least cal BC 116–AD 241 (2 σ). The domestic area of M2 was used at minimum between cal BC 55–AD 435 (2 σ), which encompasses the use of the funerary areas. An isolated human tooth from M1 [cal AD 125–435 (2 σ)] suggested that this funerary area is later than the one at the periphery of M2, and possibly contemporaneous with the later formation of the M2 shell midden. The archaeological assemblage of the “Banwaroid tradition” is widely distributed in Cuba, and mixed with other archaeological traditions, supporting that a complex web of human interactions took place in the Caribbean in precolonial times.

Holocene evolution and Anthropocene destruction of the Krishna Delta on the east coast of India: Delta lobe shifts, human impacts, and sea-level history

The Holocene evolution of the Krishna Delta was inferred using landform characteristics and 11 sediment cores with 59 Accelerator Mass Spectrometry 14C dates. The landform assemblages in a 5880 km2 area of the Krishna Delta indicate an upper (landward) river-built fluvial plain and a lower (seaward) marine-built beach-ridge plain. Holocene sediment unconformably overlying a Pleistocene basement consists of 11 sedimentary facies, mainly shallowing-upward and deltaic succession. Sea level indicators such as the basal mangrove peat layers above the Pleistocene basement and the foreshore sediments indicate that the sea level rose from −9 m to −3 m during 8.3–6.3 cal ky BP, and stabilised at the present level around 5 cal ky BP. The 3539 km2 area of the Krishna Delta beach-ridge plain developed in five major stages during the last 6 cal ky, with distinct lateral and seaward migration of delta lobes (depocentre shifts). Delta progradation accelerated in the last 500 years, forming an out-building lobate delta. However, predominant erosion along the sediment-starved coast during the past five decades, due to impoundment of riverine inputs at the burgeoning upstream dams, has pushed the Krishna Delta into a persistent destruction phase.

Paleoclimate and Holocene relative sea-level history of the east coast of India

The Holocene sea-level history of the east coast of India is relatively unexplored. We analysed a 17.37-m-long sediment core from Kolleru Lake, a fresh waterbody located in a deltaic setting along the east coast of India, to reconstruct the climate, environmental, and sea-level history of the region. Sedimentary facies and pollen assemblages, with nine accelerator mass spectrometry 14C dates (two mollusk shells and seven plant samples) from the core revealed Holocene relative sea-level changes, and provide the first insights into the climate of the region from the Last Glacial Maximum (LGM) to present. A layer of anhydrous calcium sulfate at the core bottom, along with a 14C age of 18.4 cal ka BP, combined with the absence of pollen in mottled yellowish clay, indicated a desiccated lake surface, reflecting a dry LGM climate. Palynomorphs in the overlying calcareous-concretion-bearing light brown silty clay showed a change from arid terrestrial herbaceous plants to freshwater taxa, indicating a change from dry to wet climate after the LGM and before 8.0 cal ka BP. Further upward in the core, black, sticky silty clay with abundant mangrove pollen and mollusk shells indicated a marine environment in Kolleru Lake and aggradational sediment stacking related to the middle Holocene sea-level rise from 8.0 to 4.9 cal ka BP. The uppermost sandy/silty clay, with terrestrial/aquatic pollen and a 14C age of 3.7 cal ka BP indicated a freshwater environment during the late Holocene. Our results show that Kolleru Lake, on the east coast of India, changed from a desiccated state during the dry LGM to a brackish lagoon during the middle Holocene, and then to a freshwater lake by the late Holocene, under the influence of climate and relative sea-level changes.

Complex response of weathering intensity registered in the Andaman Sea sediments to the Indian Summer Monsoon over the last 40 kyr

Downcore geochemical composition of sediment core retrieved from the central Andaman Sea were measured to help understanding the potential connection between chemical weathering and monsoon climate since the last glacial period. The age model was confirmed based on twelve accelerator mass spectrometry (AMS) 14C dates on planktonic foraminifera Neogloboquedrina dutertrei. Provenance discrimination results distinguished by Rare Earth Elements pattern and Sc/Th-(La/Yb)UCC diagram revealed that terrestrial sediment from the Irrawaddy River are the dominant input in the central Andaman Sea. Chemical weathering indexes, including chemical index of alteration (CIA), weathering index of Parker (WIP), αAlNa, and a stack of these data were reported and the terrestrial input was assessed using Ti/Ca ratios. These indexes showed general synchronicity with the regional monsoon precipitation and temperature record, the chemical weathering intensity and monsoon precipitation/temperature were stronger/higher during MIS 3 and MIS 1 and weaker/lower during MIS 2, indicating existence of a general “climate-driving weathering” pattern on glacial-interglacial time scales. However, certain anomalies occurred during 18–13 cal. kyr BP and 6–3 cal. kyr BP, when the chemical weathering intensity showed higher and lower values, respectively. The chemical weathering intensity enhanced during 18–14 cal. kyr BP, due to increased isolation and markedly increased temperatures, as well as lower erosion production and sediment transfer rate caused by lower precipitation, whereas the opposite conditions prevailed during 14–13 cal. kyr BP. Indeed, for the weak chemical weathering intensity during 6–3 cal. kyr BP, decreased isolation, relatively high terrestrial sediment supply, slightly lower precipitation and markedly lower temperatures were suggested to be the primary reasons, indicating the presence of a “climate-driving weathering” pattern on millennial time scales. Our findings support the hypothesis that the chemical weathering evolution in the north-eastern Indian Ocean was synchronous with both global and regional climate conditions, representing distinct changes controlled by Indian summer monsoon on different time scales.

Late Quaternary Deep-Sea Corals (Anthozoa: Scleractinia) from the Argentine Continental Margin

Fossil deep-sea corals have been collected from dredges and sediment cores from the outer shelf and middle slope at the northern Argentine Continental Margin (37o–38o S). They have been identified as Flabellum ( F. ) thouarsii and Bathelia candida . Both species inhabit nowadays the outer shelf and the upper and middle slope of eastern South American coasts, but they had never been described as fossils. The integration of planktonic foraminiferal assemblages and one accelerator mass spectrometry 14C dating of a fragment of a coral branch belonging to B. candida allowed a precise biostratigraphic and geochronological control, indicating a Late Pleistocene age for the first fossil representatives of this species.

Reconstructing Chemical Weathering Intensity in the Mekong River Basin Since the Last Glacial Maximum

AbstractHigh‐resolution clay mineralogy and major element geochemistry of Core SO18383‐3 collected off the Mekong River mouth in the southern South China Sea have been investigated, aiming to reconstruct sediment provenance and chemical weathering intensity since the last glaciation. The chronology is based on foraminiferal accelerator mass spectrometry 14C dates. Clay mineral analysis suggests that the Mekong River is a major sedimentary source for the studied area. The values of chemical index of alteration (CIA) indicate moderate chemical weathering in the Mekong River basin. Smectite/(illite + chlorite) and smectite/kaolinite ratios coupled with TiO2/K2O ratio reveal the temporal variation in chemical weathering intensity in the Mekong River basin. The lower ratios around the Last Glacial Maximum (29.9–14.7 cal ka BP), the Heinrich Event 1 (~14.8 cal ka BP), the Younger Dryas interval (12.4–11.3 cal ka BP), and middle to late Holocene (7.6–1.1 cal ka BP) indicate weak chemical weathering intensity. In contrast, the higher ratios occurring during the Bølling‐Allerød period (14.7–12.7 cal ka BP) and the period of main deglaciation (14.7–7.6 cal ka BP) indicate stronger chemical weathering in the Mekong River basin. The good correlations between these proxies and the available proxy records of the East Asian summer monsoon intensity suggest that the intensity of chemical weathering in the Mekong River basin over the last 30 ka is significantly controlled by the summer monsoon. This study greatly increases our understanding of the principal forcing factor on continental weathering in the Mekong River basin since the Last Glacial Maximum.