Marine Isotope Research Articles

Indian summer monsoon variability during the past ~75 ka based on stable isotope records of sediments from NW India

Here we report continuous and chronologically well-constrained records of stable oxygen (δ18O) and carbon (δ13C) isotope compositions of carbonate nodules (nodular calcretes), and δ13C of sediment organic matters (δ13CSOM) in samples from two (~48 m deep) drill-sediment cores, collected from a paleo-Yamuna channel in the NW Indo-Gangetic Plain in north Haryana. The results were used to reconstruct Indian summer monsoon (ISM) precipitation variability and paleovegetation pattern during the past ~75 ka and present a longer record of ISM variability in the Indo-Gangetic Plain. The δ18O of carbonate nodules (−7.80‰ to −4.04‰, average −6.01‰) shows a good negative covariation with variability in the model-derived intensity of ISM precipitation, indicating it to be a good proxy for ISM variability. We infer intense ISM precipitation during late marine isotope stage (MIS) 5, early and late MIS 3, and early MIS 1 periods, marked by relatively lower δ18O of carbonates. These changes in the ISM intensity are in-phase with the precession-induced changes in the Northern Hemisphere summer insolation. The δ13CSOM (−27.4‰ to −22.3‰, average −25.3‰) indicates C3-dominated vegetation in the Himalayan catchment with a noticeable increase in δ13CSOM during late MIS 4 to early MIS 3, late MIS 3, and early MIS 1 periods, which are characterized by the intense ISM (warm and moist condition). This suggests an increased abundance of C4 plants during the periods of intensified ISM precipitation. The δ13C of carbonate nodules varies from −3.63‰ to 1.56‰ (average −1.55‰). The enrichment in 13C of the carbonates is most likely due to the influence of dissolved inorganic carbon derived from the Himalayan source and/or atmospheric CO2 on the carbonate nodules. Therefore, we suggest that the δ13C of carbonate nodules from the Indo-Gangetic Plain requires a careful evaluation.

Remote and local controls on dissolved oxygen in the Western Tropical Pacific thermocline during the last 700 kyr

The dissolved oxygen level of the low-latitude Pacific thermocline is a sensitive tracer of global ocean circulation, especially at high latitudes. However, its variability covering glacial–interglacial cycles has not been well documented. Based on the thermocline-dwelling foraminiferal population extracted from Calypso Core MD06–3047, we derived a record of the Western Tropical Pacific (WTP) thermocline oxygenation over the last 700 kyr. We found that the glacial thermocline oxygenation gradually enhanced to dome-like peaks during glacial periods, with significant relative abundance of thermocline-dwelling species minimum events. We suggest that the remote physical process of lateral O2 supply (dominated by Southern Ocean (SO) ventilation and Antarctic Intermediate Water advection, with a minor contribution of North Pacific Intermediate Water (NPIW)) and the local biological process of O2 consumption (by organic biological productivity, determined by iron supply and NPIW-driven nutrient supply) may together control the WTP thermocline oxygenation on glacial–interglacial cycles. The surprisingly synchronous co-variation indicates that SO ventilation and Antarctic Intermediate Water advection have the potential to be the primary controlling factors. Furthermore, the consistent and simultaneous dramatic increments in Marine Isotope Stages 13–11 transition and each deglacial period provide robust support for a close coupling between the global (mid-Brunhes) climatic shift scenario of SO ventilation and the WTP thermocline oxygenation.

Experiments with replicas of Early Upper Paleolithic edge-ground stone axes and adzes provide criteria for identifying tool functions

Systematic tree-felling using a polished stone axe and/or adze developed with sedentary lifeways in Holocene environments. However, securely dated Pleistocene edge-ground stone axes/adzes have now been identified from Marine Isotope Stage 3 sites in two distant regions: Australia and Japan. These early ground tools are indicative of full-blown tree-felling, but whether they indeed functioned as woodworking tools remains unclear. We present the results of an experimental study with replicas of Early Upper Paleolithic edge-ground stone axes/adzes from the Japanese archipelago that included a total of 75 replicas used in 15 different use and nonuse experiments. Results indicate that identifications of wood percussive tools must be based on a comprehensive analysis of both macro- and microscopic traces. Overall, the criteria presented in this study allow us to distinguish between edge-ground stone axes/adzes used as tree-felling tools and those used for other tasks.

The microstratigraphy and depositional environments of Lida Ajer and Ngalau Gupin, two fossil-bearing tropical limestone caves of west Sumatra

Lida Ajer and Ngalau Gupin are karstic caves situated in the Padang Highlands, western Sumatra, Indonesia. Lida Ajer is best known for yielding fossil evidence that places the arrival of Homo sapiens in Southeast Asia during Marine Isotope Stage 4, one of the earliest records for the region. Ngalau Gupin recently produced the first record of hippopotamid Hexaprotodon on the island, representing the only globally extinct taxon in Pleistocene deposits from Sumatra. Microstratigraphic (micromorphological) analyses were applied to unconsolidated fossil-bearing cave sediments from these two sites. We use micromorphology as part of a micro-contextualised taphonomic approach to identify the diagenetic processes affecting fossils and sediments within these caves, through phases of their depositional history. The fossil-bearing sediments in Lida Ajer have been subjected to a suite of natural sedimentation processes ranging from water action to carnivore occupation, which would indicate the fossils underwent significant reworking prior to lithification of the deposit. The results demonstrate that the base of the unconsolidated fossil-bearing sediments in Ngalau Gupin were derived from the interior of the cave, where the matrix was partially phosphatized as a result of guano-driven diagenesis. These observations can be used to test hypotheses about the integrity of incorporated vertebrate remains and to aid in local palaeoenvironmental reconstructions. The methods employed in this research have not previously been applied to cave sediments from sites in the Padang Highlands and provide key new insights into the palaeontological and natural history of the western region of Sumatra.

Multi‐Proxy Evidence for Atlantic Meridional Overturning Circulation (AMOC) Weakening During Deglaciations of the Past 150,000 Years

AbstractDespite decades of research, the cause of deglaciations is not fully understood, leaving a critical gap in our understanding of Earth's climate system. During the most recent deglaciation (Termination I (T I)), abrupt declines in the stable carbon isotope ratio (δ13C) of benthic foraminifera occurred throughout the mid‐depth (1,500–2,500 m) Atlantic. The spatial pattern in δ13C anomalies was likely due to Atlantic Meridional Overturning Circulation (AMOC) weakening and the accumulation of respired carbon, which also yields negative excursions in carbonate ion concentration (). To investigate whether a similar pattern occurred during prior deglaciations, we developed δ13C and records from 1,800 and 2,300 m water depth in the Southwest Atlantic spanning the last 150 ka. The new records reveal negative δ13C and anomalies during Termination II (TII) and the smaller deglaciations of Marine Isotope Stages (MIS) 4/3, 5b/a, and 5d/c, suggesting AMOC weakening is a common feature of deglaciation. The anomalies are more pronounced in the shallower core following MIS 2, 4, and 6 and in the deeper core following MIS 5b and 5d. The depth‐dependent pattern is most likely due to shoaling of Northern Source Water during glacial maxima and deepening during interglacial intervals. Comparison of records from TI and TII suggests similar levels of carbon accumulation in the mid‐depth Atlantic. The Brazil Margin δ13C and results indicate the AMOC plays a key role in the series of events causing deglaciation, regardless of differences in orbital configuration, ice volume, and mean global temperature.

A zooarchaeological perspective on late pleistocene/early holocene human behaviour in the Maloti-Drakensberg region, southern Africa: The view from Ha Makotoko and Ntloana Tšoana rock-shelters, Lesotho

Re-excavation of Ha Makotoko and Ntloana Tšoana rock-shelters in western Lesotho, produced abundant faunal remains (both macro and micro) from people using the Robberg technocomplex during the late Pleistocene (Ha Makotoko and Ntloana Tšoana (15.4–13.4 kcal. BP) and early Holocene (Ntloana Tšoana 11.1–10.2 kcal. BP). This faunal material allows us to identify the subsistence strategies they employed, using the unbiased Simpson's evenness index (1-D′), and Shannon's evenness index to track diet breadth. Detailed analyses of the sites' microfauna indicates that eagle owls and/or small carnivores — not humans — were responsible for introducing them into the deposits. A chi-squared test comparing diet breadth across the sites identifies hunting strategy, focused on size 2 and 3 migratory ungulates (equids, suids, and bovids), supplemented with size 1 and 4 bovids. Comparing the evenness values from Ha Makotoko and Ntloana Tšoana to published data from other Robberg-associated sites in the wider Maloti-Drakensberg region (Sehonghong, Rose Cottage Cave and Tloutle) allows variability in subsistence strategies to be addressed. A chi-squared test comparing ungulate size classes, small mammals and fish with the evenness index reveals two important statistical differences: the warm period occupation (16.5–14.3 kcal. BP) at Rose Cottage Cave presents a narrow diet heavily focused on size 3 ungulates (with a lack of fish). At the other end of the climate spectrum, cold conditions at Sehonghong immediately before the Last Glacial Maximum were associated with a narrow diet focused on intensive fishing, with lower-than-expected numbers of size 3 ungulates. The deposits at Ntloana Tšoana, Ha Makotoko, and Tloutle, along with the Younger Dryas-associated assemblage from Sehonghong, on the other hand, present broad diets. Fish and small mammals make more of a contribution to the expanding diet in the highlands. Our approach demonstrates the flexibility that makers of Robberg tools displayed in adapting to the changing climatic and ecological conditions of this high-elevation region in the interior of southern Africa during Marine Isotope Stage 2 and across the Pleistocene/Holocene transition.

Middle Pleistocene to Holocene estuarine and aeolian deposits at L’Amélie (Médoc peninsula, Southwest France).

The chronostratigraphy of Pleistocene and Holocene coastal deposits in the Médoc Peninsula (southwest France) was revised during preventive archaeology work carried out prior to the restoration of the riprap protecting L'Amélie seaside resort. This study revealed that the Pleistocene deposits were more complex than initially expected. At the base, they comprise subtidal to supratidal estuarine units (“Argiles du Gurp”: laminated silts, green clay, sandy peat with tree stumps) related to the high sea level of Marine Isotopic Stage (MIS) 11 (Holsteinian). These deposits were incised by a fluvial/deltaic channel at the end of the interglacial, then covered by aeolian sands dating back to MIS 10. The whole area is covered unconformably by gravelly sand colluvium. Holocene aeolian deposits fill a small valley cut into the Pleistocene deposits and indicate the arrival of the coastal dune massif in the area during the late Antiquity. An overview of the results obtained in Médoc shows successive bodies of estuarine deposits indicating a gradual northward migration of the Gironde estuary. Only a few high marine levels are recorded (MIS 1, MIS 9, MIS 11, Gelasian, Piacenzian), presumably both because the sea level reached was similar to or higher than the Holocene level and because the deposits were preserved from erosion during the periods of valley incision.

Holocene stable oxygen isotope record from the North Caspian Rybachya core

The first results of 22 δ18Oost measurements on ostracod shells from the Rybachya core in the North Caspian Sea are presented. The stable oxygen isotope record here confirms previous studies of Upper Quaternary and Holocene sediments of the Rybachya core area, where it was suggested that a paleovalley was formed during the Mangyshlak regressive stage and then gradually filled during the Holocene transgressive stage. We recorded three local isotopic stages, each characterized by δ18Oost values. The hydrological variability and sea level changes associated with the transgressive-regressive rhythm of the Caspian Basin and the climatic changes in the Northern Hemisphere led to the δ18Oost changes obtained in this work. Relatively depleted δ18Oost values from sediments filling the paleovalley allowed to interpret the isotope record in terms of freshwater influx. The average δ18O enrichment of ostracod shells is taken as evidence for the isolation of the paleovalley during the Caspian Sea level retreat. However, the higher δ18Oost values obtained for the last (modern) stage of Caspian history are under the strong control of host water salinity, which is higher than during the paleovalley filling episode.

Paleoclimatic analysis of Quaternary sediments associated with the floodplain depositsof a tropical estuary along the southwestern coast of India

The coastal regions of southwest India which falls in the tropical regime, have witnessed many transgression-regression events and climatic extremes in the Quaternary Period. A core, 15 m long, was recovered from the floodplains associated with a typical backwater body (lake) in the southwestern coast of India. The granulometric analysis proved dominance of sand and silt fractions and extremely high energy conditions over the entire core. The TOC/TN ratio indicated a domination of the C4-type over the C3-type plants in the lower half of the core, suggesting a warm climate. The C3-type plants prevail in the upper part of the core, thus reflecting cool and wet environments. Extremely low values of TOC/TN ratio (0.33% to 10%) of the core indicate short periods of very high rainfall events and the rapid influx of nutrients to the basin and the eutrophication of the basin. The presence of slightly brackish, brackish/marine and marine benthic foraminifers at 12.5–9 m depth indicates episodes of transgression and regression. The derived AMS radiocarbon dates suggest the Marine Isotope Stage 3 for the lower part of the core.

Biomarker Evidence for an MIS M2 Glacial‐Pluvial in the Mojave Desert Before Warming and Drying in the Late Pliocene

AbstractAncient lake deposits in the Mojave Desert indicate that the water cycle in this currently dry place was radically different under past climates. Here we revisit a 700 m core drilled 55 years ago from Searles Valley, California, that recovered evidence for a lacustrine phase during the late Pliocene. We update the paleomagnetic age model and extract new biomarker evidence for climatic conditions from lacustrine deposits (3.373–2.706 Ma). The MBT′5Me temperature proxy detects present‐day conditions (21 ± 3°C, n = 2) initially, followed by warmer‐than‐present conditions (25 ± 3°C, n = 17) starting at 3.268 and ending at 2.734 Ma. Bacterial and archeal biomarkers reveal lake salinity increased after 3.268 Ma likely reflecting increased evaporation in response to higher temperatures. The δ13C values of plant waxes (−30.7 ± 1.4‰, n = 28) are consistent with local C3 taxa, likely expanded conifer woodlands during the pluvial with less C4 than the Pleistocene. δD values (−174 ± 5‰, n = 25) of plant waxes indicate precipitation δD values (−89 ± 5‰, n = 25) in the late Pliocene are within the same range as the late Pleistocene precipitation δD. Microbial biomarkers identify a deep, freshwater lake and a cooling that corresponds to the onset of major Northern Hemisphere glaciation at marine isotope stage marine isotope stages M2 (3.3 Ma). A more saline lake persisted for ∼0.6 Ma across the subsequent warmth of the late Pliocene (3.268–2.734 Ma) before the lake desiccated at the Pleistocene intensification of Northern Hemisphere Glaciation.

New insights on the latest Messinian-to-Piacenzian stratigraphic series from the Dahra Massif (Lower Chelif Basin, Algeria): Lago Mare, reflooding and bio-events

Geological investigations carried out on the Dahra Massif have revealed sedimentary changes and bioevents characterizing the post-gypsum detrital sediments (from Messinian to Piacenzian), which are followed by the Trubi equivalent Pliocene marls or white marly limestones. Structured into two superimposed steps, the late Messinian deposits yielded two successive ostracod assemblages. They indicate a brackish environment for the lower and a fairly open shallow brackish environment for the second. Based on their ostracod content, assemblage 1 (Cyprideis, Loxoconcha muelleri) corresponds to the Lago Mare biofacies 1 of the Apennine foredeep, which is correlated with the Lago Mare 1 episode dated between 5.64 and 5.60 Ma. Assemblage 2 (Loxocorniculina djafarovi) is referred to the Lago Mare biofacies 2 described in the same region. It is correlated with the Lago Mare 3 episode, dated between 5.46 and 5.33 Ma. Moreover, the stratigraphic succession is marked by a major discontinuity indicated by a hardground, separating step 1 from step 2 and corresponding to the ostracod assemblages 1 and 2, respectively. This discontinuity is considered here to be equivalent to the Messinian Erosional Surface, already evidenced in the region and widely known around the Mediterranean Basin. These late Messinian deposits and their ostracod assemblage 2, notably the detrital sedimentation with Ceratolithus acutus, Globorotalia margaritae, Reticulofenestra cisnerosii document a marine incursion into the Lower Chelif Basin, corresponding to the latest Messinian marine reflooding of the Mediterranean Basin, that happened before the earliest Zanclean R. cisnerosii occurrence. Finally, the bioevents evidenced in the Dahra Massif, reinforce the evidence of the late Messinian Lago Mare 3 episode, and support the ante-Zanclean age of the marine reflooding of the Mediterranean. The overlying deposits are marked by coral constructions (cf. Cladocora cf. caespitosa, Dendrophyllia sp) never described before and covering the entire early Zanclean, testifying the existence, at that time, of warm enough conditions, which may correspond to the marine isotopic stage TG5.

Evaluation of geomagnetic relative palaeointensity as a chronostratigraphic tool in the Southern Ocean: Refined Plio-/Pleistocene chronology of IODP Site U1533 (Amundsen Sea, West Antarctica)

International Ocean Discovery Program (IODP) Expedition 379 to the Amundsen Sea margin of West Antarctica recovered drill cores at two sites spanning the Latest Miocene–Holocene interval with the aim of reconstructing past West Antarctic Ice Sheet dynamics. The recovered Plio-/Pleistocene sediment sequences offer an opportunity to apply and test different dating approaches in an Antarctic deep-sea drift setting, where the records are nearly continuous and unaffected by scouring of icebergs or grounded ice. Here, through palaeomagnetic analysis of continuous u-channel samples and application of X-ray fluorescence (XRF) scanning, we revise the IODP Exp. 379 Site U1533 age model for the uppermost Pliocene and Pleistocene composite interval (0.0–2.9 Ma). We first refine the magnetostratigraphic age model with high-resolution u-channel analysis and interpreted directional data. Consistent with shipboard results, all major geomagnetic polarity chrons and subchrons are identified in the Pleistocene section. The new high-resolution u-channel dataset also allows us to identify a geomagnetic polarity excursion at ∼884 ka (interpreted as the Kamikatsura excursion) and another excursion at ∼2734 ka with confidence (potentially the Porcupine excursion). Based on the improved polarity stratigraphy, we then develop two new highly resolved age models for Site U1533 using: (i) barium enrichment cycles identified in XRF scanning data, and (ii) geomagnetic relative palaeointensity (RPI). In our first age model, we correlate cyclic variations in sedimentary barium enrichment, inferred to represent changes in export productivity, to glacial‒interglacial cycles of the Lisiecki and Raymo (2005) benthic foraminiferal oxygen isotope (δ18O) stack (LR04). Nearly all Pleistocene Marine Isotope Stages (MIS) are interpreted to be present in the barium enrichment record of Site U1533, assuming simultaneous changes in Antarctic sea-ice extent/local export productivity and global oxygen isotope stratigraphy. We then construct the second, independent age model using the Plio-/Pleistocene RPI record developed for Site U1533, which represents the longest (nearly) continuous RPI record currently available for the Antarctic margin. Comparison of the two, independently derived age models shows a variable offset, on average ± 12 kyr, with the RPI-based ages consistently older than the barium-based ages in the interval from 1.9 to 2.9 Ma and then consistently younger from 0.0 to 1.9 Ma. We interpret these offsets to result from a combination of lock-in depth effects in the younger interval (due to the relatively low sedimentation rates at this site, ∼2 cm/kyr), temporal offsets between global δ18O changes in the deep ocean and productivity response on the Antarctic margin, and/or systematic miscorrelation in the construction of the two age models. Finally, we construct a hybrid age model for the Pleistocene section of Site U1533 by combining a mixture of RPI- and barium-based age tie points that are deemed to be robust. The Site U1533 RPI record is then used, together with other Southern Ocean RPI records, to construct an Antarctic RPI stack (designated as ‘ANT-1600’) for the interval 0.0–1.6 Ma. Although sedimentation rates at two-thirds of the sites selected for the stack are lower than 10 cm/kyr, the new ANT-1600 stack is strongly coherent with the SINT-2000 RPI stack (Valet et al., 2005) on time scales of ∼20–200 kyr, allowing for its use as a regional RPI reference curve in future studies. Overall, we demonstrate that RPI at Antarctic margin/Southern Ocean sites provides a viable and valuable independent dating method for application to Plio-/Pleistocene Antarctic sediments.

Analyzing blank cutting edge efficiency associated with the adoption of microblade technology: A case study from Tolbor-17, Mongolia.

The phenomenon of lithic miniaturization during the Late Pleistocene at times coincided with increased artifact standardization and cutting edge efficiency-likely reflecting the use of small, sharp artifacts as interchangeable inserts for composite cutting tools and hunting weapons. During Marine Isotope Stage 2, Upper Paleolithic toolmakers in northern East Asia specifically used pressure techniques to make small, highly standardized lithic artifacts called microblades. However, little is currently known about how microblades affected the cutting edge efficiency of the toolkits they were a part of. We applied three methods of analyzing cutting edge efficiency to two Upper Paleolithic assemblages recently excavated from Tolbor-17, Mongolia, that document the periods before and after the introduction of microblade technology to the Tolbor Valley. A model incorporating allometric relationships between blank cutting edge length and mass suggests no difference in efficiency between the two periods, while two more conventional approaches both indicate a significant increase. The potential for improved cutting edge efficiency is only observed when the microblade sample is artificially inflated via simulation. Our results highlight challenges related to detecting and interpreting archaeological differences in cutting edge efficiency at the assemblage level.

Brazil Margin Stable Isotope Profiles for the Last Glacial Cycle: Implications for Watermass Geometry and Oceanic Carbon Storage

AbstractVertical profiles of benthic foraminiferal oxygen and carbon isotopes (δ18O and δ13C) imply the volume of southern source water (SSW) in the Atlantic basin expanded during the Last Glacial Maximum. Shoaling of the boundary between SSW and northern source water (NSW) may reduce mixing between the two watermasses, thereby isolating SSW and enhancing its ability to store carbon during glacial intervals. Here we test this hypothesis using profiles of δ18O and δ13C from the Brazil Margin spanning the last glacial cycle (0–150 ka). Shoaling of the SSW‐NSW boundary occurred during Marine Isotope Stage (MIS) 2, 4, and 6, consistent with expansion of SSW and greater carbon sequestration in the abyss. But the watermass boundary also shoaled during MIS 5e, when atmospheric CO2 levels were comparable to MIS 1. Additionally, we find there was little change in watermass structure across the MIS 5e‐d transition, the first major decline in CO2 of the last glacial cycle. Thus, the overall pattern in glacial‐interglacial geometry is inconsistent with watermass mixing acting as a primary control on atmospheric pCO2. We also find that δ13C values for MIS 5e are systematically lower than MIS 1, with the largest difference (∼1‰) occurring in the upper water column. Low δ13C during MIS 5e was most likely due to a long‐term imbalance in weathering and deposition of calcium carbonate or input of 13C‐depleted carbon from a reservoir external to the ocean‐atmosphere system.

The Middle to Late Holocene in the Agro Pontino and the Fondi basin (Lazio, Italy): A palaeogeographical overview

The Agro Pontino, a vast plain located south of Rome (southern Lazio, Italy), has served as a valuable resource for central Italian palaeogeographical, vegetational and archaeological studies for decades. This paper reviews the regional development of the Agro Pontino and adjacent Fondi basin from the Würmian (Marine Isotope Stages 2–5d) until the end of the protohistoric, with an emphasis on the period around the Early Bronze Age (EBA) date of the Avellino eruption. Following postglacial relative sea level rise, a dissected Pleistocene landscape drowned and was filled with lagoonal, fluvial, alluvial, lacustrine and marsh deposits. In the Agro Pontino, two lakes emerged divided by an alluvial fan. The unique regionally preserved stack of Middle to Late Holocene sediments, including multiple macroscopically visible tephra layers within a depositional environment, allowed for a detailed regional palaeogeographical, tephrochronological and vegetational reconstruction. This study presents the latest palaeogeographical findings from the Agro Pontino and the Fondi basin for the Middle Holocene and the EBA, for which tephra identification and dating forms the solid basis. It contributes to the reconstruction of the Pontine plain and the Fondi basin during this period and furthers our palaeoenvironmental knowledge of the conditions for human subsistence in this region during the later phase of the EBA, around the time of the Avellino eruption (c. 1900 calBC).

Millennial-scale changes in the environment, ice conditions, and deep-water ventilation at the Detroit–Tenji Seamounts, Northwest Pacific, over the last 43 kyr

The Western Subarctic Gyre (WSG) in the North Pacific represents the termination of the Atlantic Meridional Overturning Circulation (AMOC). It has been strongly influenced by periodic glaciations of adjacent landmasses, orbital- and millennial-scale variability of its environment, and ventilation, which, to date, have been poorly studied. In this study, we investigated sediment core LV76-21 recovered from the Detroit Seamount using several productivity and lithological proxies, δ18O records of planktic and benthic foraminifera (δ18Opf and δ18Obf), AMS 14C data. We also used the published results from three well-dated cores from the Detroit and Tenji Seamounts. Comparison of the δ18Opf and δ18Obf records allowed us to establish iceberg discharge events 1 and 1’ at 39–36.8 and 42–40 ka, respectively, in the WSG over the last 43 kyr. This was accompanied by considerable lightning of δ18Opf relative to the coeval δ18Obf values. The lithological results have also shown variable sea-ice influence on the regional environment during Marine Isotope Stage 3 and particularly 2, with sea ice extensions at 28.5–25.5 ka and 17.6–16.6 ka, and its significant loss since the Bølling–Allerød warming. We used high resolution δ18Obf records from studied cores as a subtle proxy of contribution of North Atlantic Deep Water (NADW) to Lower Circumpolar Deep Water (LCDW), which originating from around Antarctica and have slightly different δ18Obf values, in order to reconstruction of its spatial variability in the context of regional deep-water ventilation. The contribution of NADW to LCDW in the ventilation of the western flank of Detroit Seamount significantly increased during the interglacial and long-lasting Dansgaard–Oeschger interstadials, which was synchronous with the AMOC intensification. Over the last 43 kyr, the deep water of its eastern flank has been constantly ventilated by the LCDW with low contribution of NADW.

Environmental Changes in the Eastern Arctic during Marine Isotope Stages 80 and 81

Palynological analysis of a 317-m-long sediment core obtained from Lake El'gygytgyn (67° 30' N, 172° 05' E) located in the Eastern Arctic documents the changes in vegetation between 2.103 and 2.146 Ma. This interval encompasses marine isotope stages (MIS) 80 and 81 and includes the Reunion paleomagnetic event, an important chronological event within MIS 81. Seven pollen zones depict the varying plant communities associated with interglacial, interstadial, and glacial intervals. The warmest climatic conditions occurred during MIS 81 (pollen zone E2) when coniferous forests dominated the landscape. These forests also included moderately thermophilous broadleaf trees and shrubs. The interstade (MIS 81, pollen zone E3) is characterized by open larch forests and forest-tundra. During the period of deepest climatic cooling, which occurred at the end of MIS 80 (pollen zone E7), larch forest-tundra and shrub tundra were present across the region. The palynological analysis of sediments from Lake El'gygytgyn illustrates the varying responses of vegetation to a wide range of climatic conditions and suggests that modern Arctic communities may disappear in the future as a result of global warming.

Enhanced Asian hydroclimate instability during early MIS 6.5

Asian summer monsoon (ASM) and regional rainfall responses to external and internal forcings remain actively debated, especially at significant climate transitions. Here we present decadally-resolved stalagmite stable isotope (δ18O and δ13C) and trace element records from central China to reconstruct Asian hydroclimate variability across the Marine Isotope Stage (MIS) 7/6 transition. The results demonstrate that the maximum level of effective precipitation (or precipitation/evaporation, P/E), derived from δ13C and element records, is practically similar between MIS 7.0 and early MIS 6.5, punctuated by a series of centennial-scale moisture-deficit events, in contrast to precessional-scale ASM changes (i.e., δ18O). At millennial scale, the ASM decline is positively correlated to P/E changes, with an exponential relationship between them. It reveals that Earth's boundary conditions could differently modulate ASM and P/E changes at orbital scale, while internal forcings can generate synchronous responses. Moreover, the ASM intensity and P/E conditions exhibit enhanced instability into MIS 6, about 1.5 times in amplitude of MIS 7. These millennial-scale hydroclimate variations are in line with a rise of Northern Hemisphere summer insolation, an El Niño/La Niña transition, the increased seasonality and high-frequency tropical climate variability. Hence, low-latitude hydrological conditions could be susceptible to subtle perturbations in the climate system, providing a precondition for the arrival of MIS 6.

LA QUESTION DE L’EPIGRAVETTIEN ORIENTAL

he designation, under the name of Epigravettian, of all industries in Central and Eastern Europe from the last glacial maximum and up to the end of isotopic stage 2, masks the variety of industries and prevents an understanding of the adaptations of hunter-gatherer societies to climate variations. - For Eastern Europe (Dnieper, Boug and Don basins): Eastern Gravettian, Final Eastern Gravettian, Local Aurignacoid Industries (Muralovkian, Zamiatnine culture and others), Early Epigravettian of the steppe area, gap, Mezinian of the Dnieper Basin, late Epigravettian of the steppe area, - For the northeastern foothills of the Carpathians (Dniester, Prut and Bistrita basins) : Eastern Gravettian, Aurignacoid Industries, gap, Early Epigravettian (Molodovian s.s.), gap, Final Epigravettian, - For Central Europe: Eastern Gravettian, gap, Aurignacoid Industries, gap, Sagvarian, gap, Magdalenian and Late Epigravettian. The typological and technological studies of lithic and bone industries reveal large differences, due to strong changes in human systems during the last glacial maximum. And the mere presence of backed bladelets (which also exist in the Solutrean, Badegoulian and Magdalenian cultures in Western Europe) is not sufficient to cluster these industries under the same name of Epigravettian. So we propose to give different names to these different industries.

Controls on long-term changes in bathyal bivalve biomass: The Pleistocene glacial–interglacial record in the eastern Mediterranean

The biomass of aquatic organisms largely determines the mass and energy flow within an ecosystem, but the long-term impact of environmental change on biomass is not well constrained for a number of clades. Here, we test the hypothesis that bivalve biomass is negatively impacted by warming climate over time. This study is based on a fossil marine bivalve fauna recovered from hemipelagic sediments deposited in the eastern Mediterranean during climate cycles (marine isotope stages (MIS) 22–18; 900–712 kyr B.P.) of the Early–Middle Pleistocene Transition. We reconstruct individual shell biomasses from fossils and discuss the various biotic and abiotic factors that controlled long-term shell biomass patterns across this important interval in the Earth climate system. The results are contrary to the original hypothesis, suggesting that the response to temperature is not universal. Nevertheless, a decrease in median biomass is observed during the MIS 19 warm period and can be possibly attributed to the combined effect of multiple drivers that cooperated at that critical time in the past, including higher temperature and primary productivity, reduced ventilation of the sea floor, biodiversity changes due to geographic range shifts, and considering species- and age-specific thermal tolerances. Generally, bivalve biomass at the community level is determined by relative abundance and shell biomass-frequency distribution. In our study, the relative abundance and median biomass of small species do not increase or decrease, respectively, in warmer periods. However, larger species are negatively affected by warming both in terms of relative abundance and biomass.