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A decrease in atmospheric CO2 partial pressure (pCO2) is considered an important prerequisite for the onset and intensification of Northern Hemisphere Glaciation (NHG). However, how the ocean sequestered missing CO2 during the NHG is still uncertain. Changes in surface productivity and deep ventilation in the Southern Ocean (SO) have been proposed to explain the variations in atmospheric pCO2 over the last eight glacial cycles, but it is unclear whether these mechanisms contributed to the decrease in atmospheric pCO2 during the NHG. Using titanium-normalized contents and mass accumulation rates of biogenic opal and total organic carbon from the International Ocean Discovery Program (IODP) Expedition 374 Site U1524A, we reconstruct the productivity in the Ross Sea, Antarctica, from 3.3 Ma to 2.4 Ma. The productivity records exhibit a long-term decreasing trend and several distinct phased evolutionary features. Specifically, the local productivity fluctuated dramatically during 3.3–3.0 Ma, decreased gradually during 3.0–2.6 Ma, and remained relatively constant during 2.6–2.4 Ma. By comparing productivity with its potential influences, we infer that the phased and long-term evolutions of productivity were mainly controlled by changes in deep ocean ventilation. Sea ice expansion might have decreased productivity during 3.3–3.0 Ma by light attenuation. Changes in eolian dust input have little effect on productivity. Further analysis revealed no coupling linkage between productivity and atmospheric pCO2, indicating that the productivity in the SO Antarctic Zone (AZ) was not the main factor controlling the atmospheric CO2 decrease during the NHG. To improve our understanding of the role of SO processes in the NHG, further studies should focus on the potential influences of deep ocean ventilation on atmospheric pCO2 in the AZ, and similar studies should also be extended to the sea area in the Subantarctic Zone. [ABSTRACT FROM AUTHOR]

A decrease in atmospheric CO2 partial pressure (pCO2) is considered an important prerequisite for the onset and intensification of Northern Hemisphere Glaciation (NHG). However, how the ocean sequestered missing CO2 during the NHG is still uncertain. Changes in surface productivity and deep ventilation in the Southern Ocean (SO) have been proposed to explain the variations in atmospheric pCO2 over the last eight glacial cycles, but it is unclear whether these mechanisms contributed to the decrease in atmospheric pCO2 during the NHG. Using titanium-normalized contents and mass accumulation rates of biogenic opal and total organic carbon from the International Ocean Discovery Program (IODP) Expedition 374 Site U1524A, we reconstruct the productivity in the Ross Sea, Antarctica, from 3.3 Ma to 2.4 Ma. The productivity records exhibit a long-term decreasing trend and several distinct phased evolutionary features. Specifically, the local productivity fluctuated dramatically during 3.3–3.0 Ma, decreased gradually during 3.0–2.6 Ma, and remained relatively constant during 2.6–2.4 Ma. By comparing productivity with its potential influences, we infer that the phased and long-term evolutions of productivity were mainly controlled by changes in deep ocean ventilation. Sea ice expansion might have decreased productivity during 3.3–3.0 Ma by light attenuation. Changes in eolian dust input have little effect on productivity. Further analysis revealed no coupling linkage between productivity and atmospheric pCO2, indicating that the productivity in the SO Antarctic Zone (AZ) was not the main factor controlling the atmospheric CO2 decrease during the NHG. To improve our understanding of the role of SO processes in the NHG, further studies should focus on the potential influences of deep ocean ventilation on atmospheric pCO2 in the AZ, and similar studies should also be extended to the sea area in the Subantarctic Zone. [ABSTRACT FROM AUTHOR]

Sharks are virtually absent from coastal Antarctica since the Late Eocene glaciations, but this group exhibited a notable austral diversity during the Cretaceous and Paleogene. Several species have already been described from the Aptian-Eocene successions of the Larsen Basin exposed in the James Ross Island area (northern Antarctic Peninsula) and the predominantly deep-water Hexanchiformes have a record that, although still rare, has been continually increased. Four species of this group are currently known from that basin: Notidanodon pectinatus, Xampylodon dentatus, Rolfodon thompsoni, and Rolfodon tatere. Such records are especially concentrated in the Gamma Member of the Snow Hill Island Formation (or Herbert Sound Member of Santa Marta Formation), on James Ross Island. Here we described four teeth assigned to X. dentatus and one identified as R. tatere from upper Campanian sections of James Ross Island, highlighting the nomenclatural changes that led to the definition of Xampylodon and Rolfodon. Some specimens of X. dentatus presented here are considerably more complete or represent teeth of different positions than most previous records. The material assigned to R. tatere represents the oldest record of this species in the world, extending its time range by more than 10 million years. [ABSTRACT FROM AUTHOR]

Understanding the microscopic variability of impurities in glacier ice on a quantitative level has importance for assessing the preservation of paleoclimatic signals and enables the study of macroscopic deformational as well as dielectric ice properties. Two‐dimensional imaging via laser‐ablation‐inductively‐coupled‐plasma‐mass‐spectrometry (LA‐ICP‐MS) can provide key insight into the localization of impurities in the ice. So far, these findings are mostly qualitative and gaining quantitative insights remains challenging. Recent advances in LA‐ICP‐MS high‐resolution imaging now allow ice grains and grain boundaries to be resolved individually. These resolutions require new adequate quantification strategies and, consequently, accurate calibration with matrix‐matched standards. Here, we present three different quantification methods, which provide a high level of homogeneity at the scale of a few tens of microns and are dedicated to imaging applications of ice cores. One of the proposed methods has a second application, offering laboratory experiments to investigate the displacement of impurities by grain growth, with important future potential to study ice‐impurity interactions. Standards were analyzed to enable absolute quantification of impurities in selected ice core samples. Calibrated LA‐ICP‐MS maps indicate similar spatial distributions of impurities in all samples, while impurity levels vary distinctly: Higher concentrations were detected in glacial periods and Greenland, and lower levels in interglacial periods and samples from central Antarctica. These results are consistent with ranges from complementary meltwater analysis. Further comparison with cm‐scale melting techniques calls for a more sophisticated understanding of the ice chemistry across spatial scales, to which calibrated LA‐ICP‐MS maps now contribute quantitatively. Plain Language Summary: Compared to the large amount of information relating to paleoclimate signals reconstructed from cm‐scale impurity measurements on ice cores, knowledge about the spatial variability of impurities at the micro‐scale is extremely sparse—and becomes even more rare once quantitative datasets are concerned. However, there is an increasing demand for quantitative data for assessing the preservation of paleoclimatic signals and for the study of macroscopic deformational as well as dielectric ice properties in ice flow modeling and remote sensing. Two‐dimensional imaging via laser‐ablation‐inductively‐coupled‐plasma‐mass‐spectrometry (LA‐ICP‐MS) has shown great potential in this context, but so far, gaining reliable quantitative results for micro‐scale imaging has not been possible. Here, we present new quantification strategies that finally allow accurate calibration using ice standards. We carefully discuss the pros and cons of each method, apply the calibration to different samples from Greenland and Antarctica, and deliver the first calibrated LA‐ICP‐MS impurity maps at 40 μm resolution. Our results are consistent with bulk measurements performed on melted samples. The calibrated LA‐ICP‐MS maps will be essential for further comparison with bulk meltwater analysis, which may ultimately deliver an improved understanding of paleoclimate signals stored in deep ice. Key Points: This study presents new quantification strategies for two‐dimensional micro‐scale impurity imaging on ice cores with laser‐ablation‐inductively‐coupled‐plasma‐mass‐spectrometry (LA‐ICP‐MS)Calibrated LA‐ICP‐MS maps reveal similar spatial distributions of impurities in all ice core samples, while concentrations vary distinctlyWe developed a method to investigate the displacement of impurities by grain growth and to study ice‐impurity interactions in the laboratory [ABSTRACT FROM AUTHOR]

Only at Cape Surprise, central Transantarctic Mountains, is there exposed stratigraphic evidence for major offset along the range front, which marks a major boundary in Antarctica. Several faults parallel to the range front have been identified in the Devonian to Triassic Gondwana strata in the hinterland. Analysis of the stratigraphy based on field observations and the United States Geological Survey (USGS) aerial photographs, in conjunction with USGS topographic sheets and satellite-derived elevation measurements, suggests an array of faults with varying orientations and displacements. Fault offsets range up to an estimated 850 metres. No additional range-parallel faults have been identified and no clear pattern of faulting is evident in the hinterland of the frontal escarpment. Faulting may date from the time of slow uplift during the Cretaceous as well as the more rapid Cenozoic uplift of the range. Only a few faults in the hinterland can be allied with the fontal fault system. Cenozoic uplift and associated denudation was accompanied by glaciation of Antarctica, which is documented by Sirius Group strata. These deposits, which pre-date today's polar landscape, are older than mid Miocene, and in part may date from the earliest stages of warm-based glaciation in the early Oligocene. [ABSTRACT FROM AUTHOR]

Recently, a record of large, mostly unknown volcanic eruptions occurring during the younger half of the last glacial period (12–60 ka) has been compiled from ice-core records. In both Greenland and Antarctica these eruptions led to significant deposition of sulfate aerosols, which were likely transported in the stratosphere, thereby inducing a climate response. Here we report the first attempt to identify the climatic impact of volcanic eruptions in the last glacial period from ice cores. Average negative anomalies in high-resolution Greenland and Antarctic oxygen isotope records suggest a multi-annual volcanic cooling. Due to internal climate variability, glaciological noise, and uncertainties in the eruption age, the high-frequency noise level often exceeds the cooling induced by individual eruptions. Thus, cooling estimates for individual eruptions cannot be determined reliably. The average isotopic anomaly at the time of deposition also remains uncertain, since the signal degrades over time as a result of layer thinning and diffusion, which act to lower the resolution of both the oxygen isotope and sulfur records. Regardless of these quantitative uncertainties, there is a clear relationship of the magnitude of isotopic anomaly and sulfur deposition. Further, the isotopic signal during the cold stadial periods is larger in Greenland and smaller in Antarctica than during the milder interstadial periods for eruptions of equal sulfur deposition magnitude. In contrast, the largest reductions in snow accumulation associated with the eruptions occur during the interstadial periods. This may be the result of a state-dependent climate sensitivity, but we cannot rule out the possibility that changes in the sensitivity of the isotope thermometer or in the radiative forcing of eruptions of a given sulfur ejection may play a role as well. [ABSTRACT FROM AUTHOR]

The stability of contemporary ice shelves is under threat due to global warming, and the geological records in the Ross Sea offer such an opportunity to test the linkage between them. However, the absence of calcareous microfossils in the sediments of the Ross Sea results in uncertainties in establishing a precise chronology for studies. Hence, three sediment cores were collected and studied in terms of radiocarbon dating, magnetic susceptibility, and sediment grain size to reconstruct the environmental processes in the Ross Sea since the last glacial period. The main results are as follows: (1) two grain-size components were identified for the studied cores, which can be correlated to ice-shelf and sea-ice transport, respectively; (2) due to old-carbon contamination and an inconsistent carbon reservoir, the radiocarbon dates were generally underestimated, and as an alternative, changes in magnetic susceptibility of the studied cores can be tuned to the ice-core records to establish a reliable age–depth model and; (3) integrating sediment grain-size changes and comparisons with other paleoenvironmental proxies in the Antarctic, a process from a sub-ice sheet in the last glacial period to a sub-ice shelf in the glacial maximum, and, finally, to a glaciomarine state since the last deglacial period was identified in the western Ross Sea. Integrating these findings, the warming processes in the Antarctic were highlighted in the retreat processes of the Ross Ice Shelf in the past. [ABSTRACT FROM AUTHOR]

Buried mounds have been identified on seismic reflection profiles in the southern Roosevelt sub-basin of the eastern Ross Sea, Antarctica. Since they have never been sampled, the composition of these mounds can only be inferred from their acoustic character. Previous studies have hypothesised that they are buried glacial moraines deposited by ice grounding near the paleo-continental shelf edge, suggesting the beginning of the growth of the West Antarctic Ice Sheet (WAIS) as early as the late Oligocene. This hypothesis conflicts with earlier evidence of the WAIS advance over the central-eastern Ross Sea. An alternative explanation for the origin of the mounds, as mud volcanoes, is formulated here on the basis of seismic reflection profile reprocessing and comparison with other, better studied, mound provinces in the Ross Sea. Shallow drilling is required to verify, which hypothesis is correct, and this has implications for various WAIS scenarios, ice volumes, and thermal rheological modelling. [ABSTRACT FROM AUTHOR]

Orbital precession has been linked to glacial cycles and the atmospheric carbon dioxide (CO2) concentration, yet the direct impact of precession on the carbon cycle is not well understood. We analyze output from an Earth system model configured under different orbital parameters to isolate the impact of precession on air‐sea CO2 flux in the Southern Ocean—a component of the global carbon cycle that is thought to play a key role on past atmospheric CO2 variations. Here, we demonstrate that periods of high precession are coincident with anomalous CO2 outgassing from the Southern Ocean. Under high precession, we find a poleward shift in the southern westerly winds, enhanced Southern Ocean meridional overturning, and an increase in the surface ocean partial pressure of CO2 along the core of the Antarctic Circumpolar Current. These results suggest that orbital precession may have played an important role in driving changes in atmospheric CO2. Plain Language Summary: Over the past one million years, Earth has experienced several glacial and interglacial periods. As a glacial period is ending, carbon in the atmosphere can rise by up to 50%. The cause for this change is currently unknown, but most theories suggest that this carbon is released from the deep ocean into the atmosphere. The Southern Ocean surrounding Antarctica is the location of a lot of carbon outgassing from the deep ocean into the atmosphere, so it could be responsible for some of this change in atmospheric carbon. One of Earth's orbital cycles, precession, has been shown to change circulation in the Southern Ocean, that can affect how much carbon is carried from the deep ocean to the surface and released into the atmosphere. This paper uses simulations of a climate model to show that high precession corresponds to a 20% increase in the release of carbon from the Southern Ocean into the atmosphere. These findings suggest that precession could have affected changes in past atmospheric carbon concentrations. Key Points: Increased insolation during austral summer due to orbital precession shifts the southern westerlies polewardPoleward shifted westerlies enhance CO2 outgassing due to increased turbulent exchange and vertical transport of carbon‐rich watersEnhanced transport of carbon‐rich waters is driven by a deepening of the overturning circulation in response to poleward shifted winds [ABSTRACT FROM AUTHOR]

The East Antarctic Ice Sheet (EAIS) has its origins ca. 34 million years ago. Since then, the impact of climate change and past fluctuations in the EAIS margin has been reflected in periods of extensive vs. restricted ice cover and the modification of much of the Antarctic landscape. Resolving processes of landscape evolution is therefore critical for establishing ice sheet history, but it is rare to find unmodified landscapes that record past ice conditions. Here, we discover an extensive relic pre-glacial landscape preserved beneath the central EAIS despite millions of years of ice cover. The landscape was formed by rivers prior to ice sheet build-up but later modified by local glaciation before being dissected by outlet glaciers at the margin of a restricted ice sheet. Preservation of the relic surfaces indicates an absence of significant warm-based ice throughout their history, suggesting any transitions between restricted and expanded ice were rapid. Using satellite and survey data, an ancient river landscape 300 km wide has been discovered buried and preserved beneath the ice in East Antarctica. It has likely survived largely intact for up to 34 million years since before ice sheet growth. [ABSTRACT FROM AUTHOR]

The continuous ice core record extends 800,000 years into the past, covering the period of 100,000-year glacial cycles, but not the transition from 40,000-year glacial cycles (the Mid-Pleistocene Transition, 1.2–0.7 million years ago). A primary goal of the International Partnership in Ice Core Sciences is therefore to retrieve a 1.5-million-year-old continuous ice core, increasing our understanding of this major change in the climate system and thus of fundamental climate forcings and feedbacks. However, complex glacial processes, limited bedrock data, and surprisingly young basal ice in previous cores necessitate careful reconnaissance studies before extracting a full core. Ice borehole optical logging reflects the ice dust content and may be used to date ice quickly and inexpensively if a reference record is known. Here we explore the relationship between ice dust records and well-dated marine dust records from sediment cores in the southern Atlantic and Pacific Oceans, which lie along paths of dust sources to Antarctica. We evaluate how representative these records are of Antarctic dust both through the existing ice core record and during the older target age range, suggesting that a newly published 1.5 million year record from site U1537 near South America is likely the most robust predictor of the Oldest Ice dust signal. We then assess procedures for rapid dating of potential Oldest Ice sites, noting that the ability to detect dating errors is an essential feature. We emphasize that ongoing efforts to identify, recover, date, and interpret an Oldest Ice core should use care to avoid unfounded assumptions about the 40 kyr world based on the 100 kyr world. [ABSTRACT FROM AUTHOR]

The Eocene-Oligocene transition (ca 40–33 Ma) marks a transformation from an ice-free to an ice-house climate mode that is well recorded by oxygen stable isotopes and sea surface temperature proxies. Opening of the Southern Ocean gateways and decline in atmospheric carbon dioxide have been hypothesised as possible triggers of the major climate shift during the Cenozoic. However, identifying the driving mechanisms remains controversial and depends on a better understanding of how the different environmental changes correlate. In this study, we investigate the spatio-temporal variation in export productivity using biogenic Ba (bio-Ba) from different Ocean Drilling Program (ODP) Sites in the Southern Ocean, focusing on possible mechanisms that controlled them as well as the correlation of export productivity changes to changes in the global carbon cycle. We document two significant SO region high export productivity late-Eocene events (ca. 37 and 33.5 Ma) correlated to pronounced changes in global atmospheric p CO2. We propose that paleoceanographic changes that followed Southern Ocean gateway openings, along with more variable increases in circulation driven by episodic expansion and decline of the Antarctic ice sheet, drove enhanced SO export production in the late Eocene through basal Oligocene. These factors may have driven the episodic reduction of atmospheric carbon dioxide and contributed to Antarctic glaciation during the Eocene-Oligocene transition. [ABSTRACT FROM AUTHOR]

Climate during the last glacial period was marked by abrupt instability on millennial timescales that included large swings of temperature in and around Greenland (Daansgard–Oeschger events) and smaller, more gradual changes in Antarctica (AIM events). Less is known about the existence and nature of similar variability during older glacial periods, especially during the early Pleistocene when glacial cycles were dominantly occurring at 41 kyr intervals compared to the much longer and deeper glaciations of the more recent period. Here, we report a continuous millennially resolved record of stable isotopes of planktic and benthic foraminifera at IODP Site U1385 (the "Shackleton Site") from the southwestern Iberian margin for the last 1.5 million years, which includes the Middle Pleistocene Transition (MPT). Our results demonstrate that millennial climate variability (MCV) was a persistent feature of glacial climate, both before and after the MPT. Prior to 1.2 Ma in the early Pleistocene, the amplitude of MCV was modulated by the 41 kyr obliquity cycle and increased when axial tilt dropped below 23.5 ∘ and benthic δ18O exceeded ∼3.8 ‰ (corrected to Uvigerina), indicating a threshold response to orbital forcing. Afterwards, MCV became focused mainly on the transitions into and out of glacial states (i.e. inceptions and terminations) and during times of intermediate ice volume. After 1.2 Ma, obliquity continued to play a role in modulating the amplitude of MCV, especially during times of glacial inceptions, which are always associated with declining obliquity. A non-linear role for obliquity is also indicated by the appearance of multiples (82, 123 kyr) and combination tones (28 kyr) of the 41 kyr cycle. Near the end of the MPT (∼0.65 Ma), obliquity modulation of MCV amplitude wanes as quasi-periodic 100 kyr and precession power increase, coinciding with the growth of oversized ice sheets on North America and the appearance of Heinrich layers in North Atlantic sediments. Whereas the planktic δ18O of Site U1385 shows a strong resemblance to Greenland temperature and atmospheric methane (i.e. Northern Hemisphere climate), millennial changes in benthic δ18O closely follow the temperature history of Antarctica for the past 800 kyr. The phasing of millennial planktic and benthic δ18O variation is similar to that observed for MIS 3 throughout much of the record, which has been suggested to mimic the signature of the bipolar seesaw – i.e. an interhemispheric asymmetry between the timing of cooling in Antarctica and warming in Greenland. The Iberian margin isotopic record suggests that bipolar asymmetry was a robust feature of interhemispheric glacial climate variations for at least the past 1.5 Ma despite changing glacial boundary conditions. A strong correlation exists between millennial increases in planktic δ18O (cooling) and decreases in benthic δ13C , indicating that millennial variations in North Atlantic surface temperature are mirrored by changes in deep-water circulation and remineralization of carbon in the abyssal ocean. We find strong evidence that climate variability on millennial and orbital scales is coupled across different timescales and interacts in both directions, which may be important for linking internal climate dynamics and external astronomical forcing. [ABSTRACT FROM AUTHOR]

Knowledge of microparticle geometry is essential for accurate calculation of ice core volume-related dust metrics (mass, flux, and particle size distributions) and subsequent paleoclimate interpretations, yet particle shape data remain sparse in Antarctica. Here we present 41 discrete particle shape measurements, volume calculations, and calibrated continuous particle time series spanning 50–16 ka from the South Pole Ice Core (SPC14) to assess particle shape characteristics and variability. We used FlowCAM, a dynamic particle imaging instrument, to measure aspect ratios (width divided by length) of microparticles. We then compared those results to Coulter counter measurements on the same set of samples as well as high-resolution laser-based (Abakus) data collected from SPC14 during continuous flow analysis. The 41 discrete samples were collected during three periods of millennial-scale climate variability: Heinrich Stadial 1 (18–16 ka , n=6 ; ∼250 years per sample), the Last Glacial Maximum (LGM) (27–18 ka , n=19 ; ∼460 years per sample), and during both Heinrich Stadial 4 (42–36 ka , n=8 ; ∼620 years per sample) and Heinrich Stadial 5 (50–46 ka , n=8 ; ∼440 years per sample). Using FlowCAM measurements, we calculated different particle size distributions (PSDs) for spherical and ellipsoidal volume estimates. Our calculated volumes were then compared to published Abakus calibration techniques. We found that Abakus-derived PSDs calculated assuming ellipsoidal, rather than spherical, particle shapes provide a more accurate representation of PSDs measured by Coulter counter, reducing Abakus to Coulter counter flux and mass ratios from 1.82 (spherical assumption) to 0.79 and 1.20 (ellipsoidal assumptions; 1 being a perfect match). Coarser particles (>5.0 µm diameter) show greater variation in measured aspect ratios than finer particles (<5.0 µm). While fine particle volumes can be accurately estimated using the spherical assumption, applying the same assumption to coarse particles has a large effect on inferred particle volumes. Temporally, coarse and fine particle aspect ratios do not significantly change within or among the three time periods (p value >0.05), suggesting that long-range transport of dust is likely dominated by clay minerals and other elongated minerals. [ABSTRACT FROM AUTHOR]

The timing of the first appearance of animals is of crucial importance for understanding the evolution of life on Earth. Although the fossil record places the earliest metazoans at 572–602 Ma, molecular clock studies suggest a far earlier origination, as far back as ~850 Ma. The difference in these dates would place the rise of animal life into a time period punctuated by multiple colossal, potentially global, glacial events. Although the two schools of thought debate the limitations of each other's methods, little time has been dedicated to how animal life might have survived if it did arise before or during these global glacial periods. The history of recent polar biota shows that organisms have found ways of persisting on and around the ice of the Antarctic continent throughout the Last Glacial Maximum (33–14 Ka), with some endemic species present before the breakup of Gondwana (180–23 Ma). Here we discuss the survival strategies and habitats of modern polar marine organisms in environments analogous to those that could have existed during Neoproterozoic glaciations. We discuss how, despite the apparent harshness of many ice covered, sub‐zero, Antarctic marine habitats, animal life thrives on, in and under the ice. Ice dominated systems and processes make some local environments more habitable through water circulation, oxygenation, terrigenous nutrient input and novel habitats. We consider how the physical conditions of Neoproterozoic glaciations would likely have dramatically impacted conditions for potential life in the shallows and erased any possible fossil evidence from the continental shelves. The recent glacial cycle has driven the evolution of Antarctica's unique fauna by acting as a "diversity pump," and the same could be true for the late Proterozoic and the evolution of animal life on Earth, and the existence of life elsewhere in the universe on icy worlds or moons. [ABSTRACT FROM AUTHOR]

The Eocene‐Oligocene Transition (EOT) at ∼34 Ma marked a climatic shift from greenhouse to icehouse conditions, toward long‐lasting lower global temperatures and a continental ice sheet in the Antarctic. We report on sedimentological and inorganic geochemical results across the EOT at Ocean Drilling Program (ODP) Site 696 in the Weddell Sea, within the Antarctic limb of the Atlantic circulation. The geochemical composition of detrital, authigenic and biogenic marine sediment components, and sortable silt proxies demonstrate the impact of ice growth on high latitude water masses. Sortable silt grain size and Zr/Rb ratios attest to a period of vigorous circulation at ∼36.2–35.8 Ma, coincident with a known warm interval in the Southern Ocean. Across the EOT, detrital provenance suggests that regional ice growth in the western Weddell Sea was stepwise, first expanding in the Antarctic Peninsula, followed by parts of West Antarctica. In conjunction with regional ice growth, high uranium enrichment factors (U EF) in sediments spanning the EOT interval indicate anoxic conditions in the sediment with evidence of carbonate dissolution. Following glacial expansion and sea‐ice formation at ∼33.6 Ma, a return to oxic conditions and carbonate preservation is observed with excess barium and phosphorous indicative of an increase in productivity, and potentially carbon export. Our results highlight the important connections between ice growth and the changing properties of high‐latitude water masses at the EOT with impacts on the global ocean circulation. Plain Language Summary: Here we show how the establishment of a marine ice sheet in Antarctica during a climate transition ca. 34 Ma impacted the oceanography of the Weddell Sea using a paleoclimate archive extracted from a sediment core. The Weddell Sea is an embayment to the south of the Atlantic Ocean where the global ocean circulation interacts with the largest ice shelf of floating land ice in the world. Grain size data and geochemical results on 37 to 32 Myr old sediment provide evidence of an episode of intense ocean circulation preceding ice growth, with slowing currents, high‐latitude ocean stratification and acidification in the Weddell Sea as the ice sheet began to grow. These results show a strong coupling between ice sheet and ocean at high latitude with potential wider implications for the understanding of the climate system. Key Points: Sortable silt and Zr/Rb show vigorous circulation in a warm period ∼36 Ma declining during the Late Eocene onset of Antarctic glaciationMud provenance shows stepwise regional ice expansion with cooling in response to early Oligocene glaciation of West Antarctic terranesTrace element enrichments highlight the impact of Antarctic glaciation on primary productivity, redox and carbonate saturation state [ABSTRACT FROM AUTHOR]

Aim: The historical biogeography of the Antarctic terrestrial flora remains poorly studied and understood. Long‐term in situ persistence of mosses was demonstrated but region‐wide phylogeographical patterns and processes which shaped extant ranges remain largely unknown. Based on a circum‐Antarctic phylogeography, we aim to explore the location of glacial refugia, especially the possibility of their existence in the continent, patterns of possible connections between extant discrete populations, local colonisation routes and barriers to gene flow, hence relative importance of connectivity and isolation. Location: Antarctica, South America, Australia and New Zealand. Taxon: Syntrichia sarconeurum Ochyra & R.H.Zander (Pottiaceae). Methods: We used a range‐wide, taxonomically informed sampling and multilocus sequencing of nuclear and chloroplast DNA regions. The temporal evolutionary framework, spatial genetic structure and regional diversification were assessed using phylogenetic reconstruction (maximum likelihood and Bayesian inference), molecular dating, phylogeographical analyses and reconstruction of ancestral areas. Results: We found a striking genetic structure of the Antarctic Syntrichia sarconeurum populations that deviates from previous reports on mosses. The presence of two allopatric cpDNA haplotypes indicated a long‐term isolation of the continental populations. Nuclear ITS revealed three major lineages with a main genetic break largely consistent with plastid data. Significant phylogeographical structure was further supported by NST/FST comparison, raggedness index and mismatch analyses. Diversification of the Antarctic lineages occurred within the Pleistocene, since about 1.36 Ma. Main Conclusions: The genetic break genetic break revealed in the phylogeographical structure coincides with the Gressit line, a biogeographical separation area between the biota of the Antarctic Peninsula and the main continental Antarctica. It indicates limited connectivity of populations and suggests that S. sarconeurum has survived in multiple refugia both in the peripheral areas of the Antarctic and within the continent over several glacial periods. Differences in genetic diversity observed between these areas may hypothetically reflect asymmetric changes in reproductive mode in the past. [ABSTRACT FROM AUTHOR]

The Larsemann Hills, near Prydz Bay is a key region to understand past glacial dynamics in East Antarctica. However, multi-proxy dating constraints for this area indicate an uncertain chronology for deglaciation history during the Last Glacial Period (LGP). In this paper, we report two 26Al exposure ages and eighteen 10Be exposure ages for bedrock samples to better understand past glacial histories. The minimum exposure ages range from 82.84 ± 4.67 ka to 15.1 ± 1.95 ka corresponding to Marine Isotope Stages (MIS) 5–2, and fourteen of these samples date from before the global Last Glacial Maximum (c. 19–26.5 ka). Analysis of 10Be and 26Al concentrations implies a complex deglaciation history, and surface lowering of bedrock may have caused systematic age underestimation. Further comparisons between two adjacent regions in the Mirror Peninsula reveal two major deglaciations involving the Lambert Glacier / Amery Ice Shelf System dated at 61.78 ka to 82.84 ka and 21.98 ka to 49.5 ka during the LGP. • We present new evidence for studying glacial history of Larsemann Hills, Antarctica. • Cosmogenic nuclides 10Be and 26Al dating method is applied for better analysis. • Two major deglaciation events occurred regionally within MIS 2–3 and MIS 4–5. • The exposure age and elevation show a highly significant positive correlation. • Multi-proxy and adjacent evidence are summarized and compared with this study. [ABSTRACT FROM AUTHOR]

The Antarctic continent reached its current polar location ~83 Ma and became shrouded by ice sheets ~34 Ma, coincident with dramatic global cooling at the Eocene-Oligocene boundary. However, it is not known whether the first Antarctic glaciers formed immediately prior to this or were present significantly earlier. Here we show that mountain glaciers were likely present in the Transantarctic Mountains during the Late Palaeocene (~60–56 Ma) and middle Eocene (~48–40 Ma). Temperate (warm-based) glaciers were prevalent during the Late Eocene (~40–34 Ma) and, in reduced numbers, during the Oligocene (~34–23 Ma), before larger, likely cold-based, ice masses (including ice sheets) dominated. Some temperate mountain glaciers were present during the Miocene Climatic Optimum (~15 Ma), before a widespread switch to cold-based glaciation. Our findings highlight the longevity of glaciation in Antarctica and suggest that glaciers were present even during the Early-Cenozoic greenhouse world. This study finds that glaciers have existed in the Transantarctic Mountains for the past 60 million years, and that warm-based mountain glaciers were present in Antarctica long before ice sheets came to dominate the continent. [ABSTRACT FROM AUTHOR]

The Early Jurassic Butcher Ridge Igneous Complex (BRIC) in the Transantarctic Mountains contains abundant and variably hydrated silicic glass which has the potential to preserve a rich paleoclimate record. Here we present Fourier Transform Infrared Spectroscopic data that indicates BRIC glasses contain up to ~8 wt.% molecular water (H2Om), and low (<0.8 wt.%) hydroxyl (OH) component, interpreted as evidence for secondary hydration by meteoric water. BRIC glasses contain the most depleted hydrogen isotopes yet measured in terrestrial rocks, down to δD = −325 ‰. In situ 40Ar/39Ar geochronology of hydrated glasses with ultra-depleted δD values yield ages from 105 Ma to 72 Ma with a peak at c. 91.4 Ma. Combined, these data suggest hydration of BRIC glasses by polar glacial ice and melt water during the Late Cretaceous, contradicting paleoclimate reconstructions of this period that suggest Antarctica was ice-free and part of a global hot greenhouse. Analysis of volcanic glass from the Transantarctic Mountains suggests that 90 Million years ago glaciation was widespread in Antarctica, a period in Earth's history when the continent was considered to be ice-free and part of a global greenhouse. [ABSTRACT FROM AUTHOR]

In blue-ice areas (BIAs), deep ice is directly exposed at the surface, allowing for the cost-effective collection of large-sized old-ice samples. However, chronostratigraphic studies on blue-ice areas are challenging owing to fold and fault structures. Here, we report on a surface transect of ice with an undisturbed horizontal stratigraphy from the Larsen BIA, northern Victoria Land, East Antarctica. Ice layers defined by dust bands and ground-penetrating radar (GPR) surveys indicate a monotonic increase in age along the ice flow direction on the downstream side, while the upstream ice exhibits a potential repetition of ages on scales of tens of meters, which result from a complicated fold structure. Stable water isotopes (δ18 O ice and δ2 H ice) and components of the occluded air (i.e., CO 2 , N 2 O, CH 4 , δ15 N–N 2 , δ18 O atm (=δ18 O-O 2), δ O2/N2 , δ Ar/N2 ​​​​​​​, 81 Kr, and 85 Kr) are analyzed for surface ice and shallow ice core samples. Correlating δ18 O ice , δ18 O atm , and CH 4 records from the Larsen BIA with ice from previously drilled ice cores indicates that the gas age at various shallow vertical coring sites ranges between 9.2–23.4 kyr BP, while the ice age sampled from the surface ranges from 5.6 to 24.7 kyr BP. Absolute radiometric 81 Kr dating for the two vertical cores confirms ages within acceptable levels of analytical uncertainty. A tentative climate reconstruction suggests a large deglacial warming of 15 ± 5 ∘ C (1 σ) and an increase in snow accumulation by a factor of 1.7–4.6 (from 24.3 to 10.6 kyr BP). Our study demonstrates that BIAs in northern Victoria Land may help to obtain high-quality records for paleoclimate and atmospheric greenhouse gas compositions through the last deglaciation, although in general climatic interpretation is complicated by the need for upstream flow corrections, evidence for strong surface sublimation during the last glacial period, and potential errors in the estimated gas age–ice age difference. [ABSTRACT FROM AUTHOR]

The Transantarctic Mountains are an important corridor between the East Antarctic Ice Sheet and the Western Ross Sea, where most current ice streams and outlet glaciers arise. We investigated Ricker Hills, the largest exposed mountainous region between Southern Victoria Land and Terra Nova Bay, and dated the glacial landforms using in-situ cosmogenic-nuclide 10Be surface exposure dating to reconstruct the paleo-glacial dynamics. The surface of the Hollingsworth glacier lowered since the middle of Marine Isotope Stage (MIS) 2 (22.1 ka); therefore, the Last Glacial Maximum (LGM) occurred before that period. Cosmogenic, geomorphic, and climatic records constrained the glacial surface slope to be between 5.4° and 6.8°. The ice was 270–320 m thicker at the LGM (MIS 2) than presently but did not override the top surface of the Benson Knob. Moreover, previous glacial periods such as the local LGM (MIS 4) or Penultimate Glacial Maximum (MIS 6) maintained thicker ice than the LGM (MIS 2). The Ross Ice Shelf opening during the mid-Holocene (∼6 ka) caused the rapid collapse of the terminal outlet glaciers and supplied notable snow accumulation upstream, which stagnated lowering. The greatest lowering and retreat occurred during the late Holocene (2.3 ∼ 0.8 ka), when elephant seal colonies thrived in the Ross Embayment. [ABSTRACT FROM AUTHOR]

Large volcanic eruptions occurring in the last glacial period can be detected by their accompanying sulfuric acid deposition in continuous ice cores. Here we employ continuous sulfate and sulfur records from three Greenland and three Antarctic ice cores to estimate the emission strength, the frequency and the climatic forcing of large volcanic eruptions that occurred during the second half of the last glacial period and the early Holocene, 60–9 kyr before 2000 CE (b2k). Over most of the investigated interval the ice cores are synchronized, making it possible to distinguish large eruptions with a global sulfate distribution from eruptions detectable in one hemisphere only. Due to limited data resolution and large variability in the sulfate background signal, particularly in the Greenland glacial climate, we only list Greenland sulfate depositions larger than 20 kgkm-2 and Antarctic sulfate depositions larger than 10 kgkm-2. With those restrictions, we identify 1113 volcanic eruptions in Greenland and 737 eruptions in Antarctica within the 51 kyr period – for which the sulfate deposition of 85 eruptions is found at both poles (bipolar eruptions). Based on the ratio of Greenland and Antarctic sulfate deposition, we estimate the latitudinal band of the bipolar eruptions and assess their approximate climatic forcing based on established methods. A total of 25 of the identified bipolar eruptions are larger than any volcanic eruption occurring in the last 2500 years, and 69 eruptions are estimated to have larger sulfur emission strengths than the Tambora, Indonesia, eruption (1815 CE). Throughout the investigated period, the frequency of volcanic eruptions is rather constant and comparable to that of recent times. During the deglacial period (16–9 kab2k), however, there is a notable increase in the frequency of volcanic events recorded in Greenland and an obvious increase in the fraction of very large eruptions. For Antarctica, the deglacial period cannot be distinguished from other periods. This confirms the suggestion that the isostatic unloading of the Northern Hemisphere (NH) ice sheets may be related to the enhanced NH volcanic activity. Our ice-core-based volcanic sulfate records provide the atmospheric sulfate burden and estimates of climate forcing for further research on climate impact and understanding the mechanism of the Earth system. [ABSTRACT FROM AUTHOR]

Antarctic fjords and coastal bays are excellent traps for sediment and represent key areas for high-resolution investigation of past environmental conditions. Robertson Bay is an understudied coastal area located at the confluence of the Ross Sea and the Southern Ocean. Recently obtained seafloor morphology data indicate the presence of a cross-shelf elongated valley, composed of three minor basins separated by sills and seabed ridges with an arcuate shape. Several cores were collected within the basins, and investigated using a multiproxy approach including sedimentological, chemical, geochemical, and micropaleontological characterization to reconstruct the paleoenvironmental evolution from the last glacial period to present. The ages of two of these cores are constrained using ramped pyrolysis oxidation radiocarbon dating. Four sedimentary facies were recognised from which we developed a sedimentary model covering the last 21,000 years (21 ka BP). Our record provide evidence for a covering ice shelf cover from 21 to 16.5 ka BP, which gradually receded between 16,5 and 11 ka BP due to the progressive intrusion of modified Circumpolar Deep Water, thereby promoting the formation of Ice Shelf Water and High Salinity Shelf Water. From 11 to 5,8 ka BP, the ice shelf continued shrinking and nutrient-rich of modified Circumpolar Deep Water penetration onto the continental shelf progressively favoured diatom blooms and a general increase in primary productivity until 5.8 ka BP. The Late Holocene is characterised by an alternation of prolonged sea ice cover with stratified water column and strong bottom current with prolonged sea-ice free season with the intrusion of modified Circumpolar Deep Water and very slow energy bottom current. • First paleoenvironmental study from the LGM to the present in Robertson Bay. • Strong impact of regional ice sheet recession on environmental conditions and productivity. • Multiproxy approach constrained by Ramped Pyrolysis based age model. • The coastal bay area was studied by sediment cores and geophysical data. [ABSTRACT FROM AUTHOR]

Antarctic sea ice is a critical component of the climate system affecting a range of physical and biogeochemical feedbacks and supporting unique ecosystems. During the last glacial stage, Antarctic sea ice was more extensive than today, but uncertainties in geological (marine sediments), glaciological (ice core), and climate model reconstructions of past sea-ice extent continue to limit our understanding of its role in the Earth system. Here, we present a novel archive of past sea-ice environments from regurgitated stomach oils of snow petrels (Pagodroma nivea) preserved at nesting sites in Dronning Maud Land, Antarctica. We show that by combining information from fatty acid distributions and their stable carbon isotope ratios with measurements of bulk carbon and nitrogen stable isotopes and trace metal data, it is possible to reconstruct changing snow petrel diet within Marine Isotope Stage 2 (ca. 24.3–30.3 cal kyr BP). We show that, as today, a mixed diet of krill and fish characterizes much of the record. However, between 27.4 and 28.7 cal kyr BP signals of krill almost disappear. By linking dietary signals in the stomach-oil deposits to modern feeding habits and foraging ranges, we infer the use by snow petrels of open-water habitats ("polynyas") in the sea ice during our interval of study. The periods when consumption of krill was reduced are interpreted to correspond to the opening of polynyas over the continental shelf, which became the preferred foraging habitat. Our results show that extensive, thick, and multiyear sea ice was not always present close to the continent during the last glacial stage and highlight the potential of stomach-oil deposits as a palaeoenvironmental archive of Southern Ocean conditions. [ABSTRACT FROM AUTHOR]

The published latest Palaeocene to Early–Middle Eocene age limits of the Sabrina microfloras, offshore Aurora Subglacial Basin, East Antarctica, largely depend on 1970s age-range data for fossil pollen and spore species in the continental margin basins of southern Australia. This paper uses updated biostratigraphical data from southern Australia, including the basins closest to the Aurora Basin throughout the Late Cretaceous and Paleogene, to propose that the age of the terrestrial component of the Sabrina microfloras is Campanian to Maastrichtian, not Paleogene. However, the revised age limits do not preclude these microfloras being redeposited more or less intact during the development and expansion of ice-sheets on East Antarctica, i.e. most probably during the late Paleogene based on other evidence from East Antarctica. [ABSTRACT FROM AUTHOR]

An accurate reconstruction of the Antarctic Ice Sheet is essential in order to develop an understanding of ice-sheet responses to global climate changes. However, the erosive nature of ice-sheet expansion and the difficulty of accessing much of Antarctica make it challenging to obtain field-based evidence of ice-sheet and sea-level changes before the Last Glacial Maximum. Limited sedimentary records from Lützow-Holm and Prydz Bays in East Antarctica demonstrate that the sea level during Marine Isotope Stage 3 was close to the present level despite the global sea-level drop lower than -40 m. We demonstrate glacial isostatic adjustment modeling with refined Antarctic Ice Sheet loading histories. Our experiments reveal that the Indian Ocean sector of the Antarctic Ice Sheet would have been required to experience excess ice loads before the Last Glacial Maximum in order to explain the observed sea-level highstands during Marine Isotope Stage 3. As such, we suggest that the Antarctic Ice Sheet partly reached its maximum thickness before the global Last Glacial Maximum. [ABSTRACT FROM AUTHOR]

The 17O-excess (Δ17O) of sulfate (SO 4 2−) in Antarctic ice cores is a potential tool for assessing past oxidant chemistry. However, a significant gap between atmospheric and ice core Δ17O(SO 4 2−) has been reported in Antarctica. Here, we report Δ17O(SO 4 2−) of surface snow at sites with different snow accumulation rates along a latitudinal traverse route in East Antarctica. While the Δ17O(nss-SO 4 2−) values for the coastal region showed an average of 1.0 ± 0.5‰ (n = 8) that can be explained by atmospheric Δ17O(SO 4 2−) variations, Δ17O(nss-SO 4 2−) in the katabatic (2.7 ± 0.2‰, n = 5) and inland (3.5 ± 0.3‰, n = 6) regions showed relatively high values that cannot be explained only by atmospheric deposition. Lower methanesulfonate (MSA) fluxes and lower mass ratios of MSA to SO 4 2−, along with higher Δ17O(nss-SO 4 2−) values, were observed in the katabatic and inland regions, suggesting the production of SO 4 2− with a high Δ17O value through MSA oxidation via OH radicals. The influence of this chemical post-depositional effect on MSA and Δ17O(SO 4 2−) is more pronounced in the inland compared to the katabatic region. The Δ17O(SO 4 2−) records in Antarctic ice cores with low accumulation rates may be impacted by elevated Δ17O(SO 4 2−) values originating from MSA oxidation, necessitating careful interpretation. In particular, the shift in Δ17O(SO 4 2−) from glacial to interglacial periods, previously interpreted as a change in atmospheric sulfate formation, requires reconsideration. • Antarctica has a discrepancy of atmospheric and ice core Δ17O(SO 4 2−). • Δ17O(nss-SO 4 2−) in snow differs latitudinally from coastal to inland regions. • Interpretation of ice core Δ17O(SO 4 2−) needs caution with considering the post-depositional change. [ABSTRACT FROM AUTHOR]

Milankovitch orbital parameters control cycles of insolation, a primary pacer of long term changes in climate, but exactly how insolation signals are transmitted around the globe in the climate system is unclear. In order to address the fundamental questions of when and how ice age climates begin and end, how fast glaciers retreated during the last deglaciation, and how glaciers behaved before anthropogenic influence, we need robust glacial chronologies. The timing of local glacial maxima beyond the last glacial cycle, however, has remained largely unconstrained due to moraine degradation over time, limiting our ability to fully explore these questions. By developing a detailed geomorphic surficial map and targeting relatively tall, ridge-top boulders, we have constructed a new, precise 10Be chronology of glacial maxima of the Ñirehuao glacier lobe (45°S) for the last two glacial cycles. We report one of the first directly dated records of a MIS 6 glacier advance in Patagonia, which formed a major set of moraines by at least 153 ± 5.1 ka, with a stillstand or smaller readvance by 137 ± 4.2 ka, corresponding to the two coldest and dustiest periods of MIS 6 in Antarctica. The next largest advance occurred at 23.6 ± 0.9 ka, at the end of peak Southern Hemisphere MIS 2 cooling. Retreat of the glacier commenced by ∼18.5 cal ka BP when lakes in a tributary valley just to the southwest became ice-free. Overall we find that advances of the Ñirehuao glacier lobe occur when winter sea ice around Antarctica is expansive and both obliquity and eccentricity are at their minima. • We present a new, detailed geomorphic map and 10Be chronology of the Ñirehuao glacier lobe for the last two glacial cycles • We report one of the first directly dated records of a MIS 6 glacier advance in Patagonia • The Ñirehuao glacier lobe formed a major set of moraines by 153±5.1 ka with a stillstand or smaller readvance by 137±4.2 ka • The MIS 2 glacial maximum occurred at 23.6±0.9 ka and subsequent retreat of the glacier commenced by ∼18.5 cal ka BP • Overall, advances occurred when winter sea ice around Antarctica was expansive and obliquity and eccentricity were at minima [ABSTRACT FROM AUTHOR]

We use geophysical data together with a recent subglacial bedrock map (BEDMACHINE model) to obtain and investigate a new three-layer sediment model for Antarctica that locally improves the global sediment model. We provide a combined, continuous, sediment model for Antarctica and surrounding oceans by joining such improved continental sedimentary model with an existing global one (GlobSed). Our results reveal large differences between sedimentary basins for Antarctica due to their age and origin. The maximum thickness of sediments is reached under Filchner-Ronne Ice Shelf and off the Weddell Sea coast (10–12 km); further offshore, towards the ocean, the thickness of sediments drops to 4–5 km. We divide the sediment cover into three layers to distinguish material with different velocities. The lower sediment layer (deeper than 7 km) with high P-wave velocities (4.0–4.9 km/s) is found only for Lambert Rift and Filchner-Ronne basin. The middle layer (2–7 km) has large variations for different sedimentary basins: 3.5–3.7 km/s for Lambert Basin; 4.0–4.3 km/s for Ross, Byrd and Bentley basins; 3.3–4.0 km/s for Filchner-Ronne Basin. The upper sediment layer (0–2 km) has large velocity variations, from 2.0 km/s for Ross and Lambert basins (young sediments) to 4.7 km/s for Dronning Maud Land basins. We suggest that P-wave velocities larger than 4 km/s represent old, compacted sediments which belong to the Beacon Supergroup; about 3 km/s refer to Mesozoic (rifted?) sediments; and less than 3 km/s relate to young Cenozoic sediments. According to this criterion, Dronning Maud Land, Bentley and Byrd basins belong to the Beacon Supergroup, while more complex and thicker Ross, Lambert and Filchner-Ronne basins contain sediments from Beacon Supergroup in the middle or lower layer, respectively. Other sedimentary basins with more moderate velocities possibly belong to the East Antarctic Rift System which formed later during Gondwana breakup. [Display omitted] • We combine new seismic data, and two existing models, to produce a new representation for the layered structure of sediments in Antarctica and neighbouring oceans • Several types of sedimentary basins are recognized: parts of the Beacon Supergroup, and more recent rifting basins. • The deepest Filchner-Ronne basin has a complex structure with multi-layered sediments (up to 12 km). • Seismically-derived P wave velocities in the sediments vary from 2.0 km/s for Ross Ice Shelf Basin (young sediments) to 4.7 km/s for Dronning Maud Land Basin. • Rifting in the East Antarctic Rift System appears to have continued after glaciation. [ABSTRACT FROM AUTHOR]

Brine formed through the cryogenic concentration of seawater remains one of the least understood components of Earth's cryosphere. Cryogenic brine is a prominent feature of the McMurdo region of Antarctica, where it has been documented below the Taylor Glacier, in numerous ice-covered lakes in the McMurdo Dry Valleys, and in an extensive, seaward-flowing groundwater system in the Taylor Valley. A much larger and less studied body of brine exists offshore in the McMurdo Sound subsurface, where it saturates the pore space and has precipitated intergranular cement in Cenozoic glaciomarine strata deep within the Victoria Land Basin. This review examines the nature and distribution of brine in the McMurdo region to assess its volume, genesis, and significance. Constraints on subsurface fluid migration are considered in the context of available data. Geochemical data indicate that the brine is the product of seawater freezing, with water-rock interaction and evaporation, especially in the McMurdo Dry Valleys where brines stayed close to the surface, leading to further compositional modification. The volume of brine in the region is currently estimated at 27,000 km3. However, accounting for the widespread distribution of brine-precipitated carbonate cement requires that a much larger volume of brine moved through the subsurface in the past. Brine geochemistry is consistent with a genetic relationship between brine in the Taylor Valley and offshore in the subsurface of the Victoria Land Basin. Chronostratigraphic constraints point toward episodic, rather than continuous brine formation. A proposed scenario involves flooding of the McMurdo Dry Valleys during Neogene periods of relative warmth to form fjord-like systems, which were then cut off during subsequent cooling and ice sheet growth. Isolated bodies of seawater were concentrated via freezing to form brine, which percolated into the subsurface and flowed seaward. Among the enduring features that may record the presence of brine in the geologic record, brine-precipitated cement phases hold the most promise for preservation on Earth as well as on Mars. [ABSTRACT FROM AUTHOR]

Millennial-scale climate oscillations of the last ice age registered in Greenland and Antarctic ice cores did not always vary in unison. A striking example is that the strongest Antarctic warming episodes occurred during Heinrich episodes in the North Atlantic region. Although the bipolar seesaw affords a possible explanation for such anti-phasing, it does not account for the equally striking observation that climate varied in unison between the hemispheres about half the time. Such phasing differences suggest the need for an alternative hypothesis in which the polar regions at times responded in unison to common forcing, and at other times left the impression of a bipolar seesaw. We posit that this impression arose from the effect of warmer-than-usual summers on continental ice sheets adjacent to the North Atlantic Ocean during each Heinrich episode. The relatively warm Heinrich summers produced discharges of meltwater and icebergs of sufficient volume to stimulate very cold winter conditions from widespread sea ice on a freshened ocean surface. The intervals between Heinrich episodes featured relaxation of sea-ice-induced winter severity from reduced summertime influx of meltwater and icebergs, indicating relatively cooler summer conditions. It is postulated that the causative variations in freshwater fluxes were driven by a climate signal most evident in Antarctic ice cores but also recognized in other paleoclimate records in both polar hemispheres. We suggest that this widespread signal arose from changes in the latitude and strength of the austral westerlies and the resulting effect on the western Pacific tropical warm pool, a mechanism dubbed the Zealandia Switch. • Bipolar synchrony of millennial-scale glacier melt during the last glaciation. • Interhemispheric glacier signal inconsistent with 'bipolar seesaw' hypothesis. • Northern 'stadials' attributed to warm summers paired with extremely cold winters. • Enhanced melt-induced northern seasonality obscured global ice-age climatic signature. • Differentiating summer from winter effects key to interpreting paleoclimatic proxies. [ABSTRACT FROM AUTHOR]

Precise ice-core chronologies are essential for identifying the timing and duration of polar climatic changes as well as their phasing with the changes in other parts of the globe. However, existing ice-core chronologies beyond the last 60 kyr show relatively large disagreements with each other and with U–Th chronologies of speleothems. Here, we constructed new ice and gas age scales for the Dome Fuji (DF) core (DF2021) over the last 207 kyr by combining a Bayesian dating model and firn densification model, constrained by various types of chronological and glaciological information including new δO 2 /N 2 age markers, precise synchronization to other high-quality chronologies (volcanic, cosmogenic, and CH 4 signals), and high-resolution δ15N of N 2 (reflecting past firn thickness). The new chronology is tightly constrained by synchronization to other well-dated records for the last 60 kyr, whereas it is independent from other chronologies for the older period. For the last 60 kyr, the DF2021 chronology agrees with the layer-counted ice core chronologies (GICC05 and a part of WD2014) and U–Th chronologies of speleothems within ∼200 years. For the period 60–130 kyr BP, the timing of all Dansgaard-Oeschger warming events on DF2021 agree with those of corresponding events in the U–Th dated Chinese or European speleothems mostly within 1 kyr (well within 2σ uncertainty of DF2021). The excellent agreement suggests high accuracy of our chronology, and supports the assumption of negligible phasing between the past local summer solstice insolation and δO 2 /N 2 fractionation at bubble close-off (the basis for constructing the δO 2 /N 2 age markers). Between 130 and 207 kyr BP (penultimate glacial period), there is a lower degree of similarity between the variations in atmospheric CH 4 and speleothem calcite δ18O than in the last glacial period, making the age comparison challenging. The comparison of DF2021 with 9 U–Th dates at 7 abrupt events shows the mean difference of −0.2 ± 0.8 kyr, which is within the DF2021 uncertainty (on the order of 1.5 kyr). The DF2021 chronology agrees with the AICC2012 chronology within 2 kyr except between ∼103 and 128 kyr BP where AICC2012 is likely too young by up to ∼4 kyr. By analyzing the lag between δ18O of O 2 (δ18O atm) on DF2021 and 65°N summer solstice insolation, the relatively large error in AICC2012 is found to originate in three δ18O atm age markers assuming a constant lag, which are off by more than 3 kyr. The phasing between δ18Ο atm and orbital forcing identified in this study may be useful for future ice core dating, especially where other age constraints are weak or lacking. • Coherent ice and gas age scales of the Dome Fuji (DF) core for the last 207 kyr. • Bayesian dating model, firn densification model and new ice core data are used. • The new chronology agrees with U–Th chronology of speleothems mostly within 1 kyr. • Phasing between δO 2 /N 2 and local summer insolation is negligible for the DF core. • Variable phasing between δ18O of O 2 and orbital forcing is quantified. [ABSTRACT FROM AUTHOR]

Understanding how ocean circulation has varied around Antarctica in the past is vital because significant volumes of ice are grounded below sea level, and therefore ice sheet variations are strongly coupled with oceanographic variability at the continental shelf margin. This study investigates the 11.75 m sediment core RS15-LC42, retrieved from the Central Basin of the Ross Sea. A magneto-biostratigraphic age model was constructed from a magnetic reversal stratigraphy, diatom biostratigraphy, and the relative paleointensity of the geomagnetic field. The core spans the last 1.34 Myr with a mean sedimentation rate of 0.88 cm/kyr, providing insights into paleoceanographic variability in the Ross Sea throughout the Pleistocene. Winnowed deposits enriched in iceberg rafted debris were formed due to a combination of enhanced glacial calving during glacial retreats, and export of Dense Shelf Water during interglacial and weak glacial periods when the ice-sheet was not grounded in the outer Joides Trough. During periods where the ice sheet grounded on the outer Ross Sea continental shelf, laminated sediments rich in reworked diatoms are interpreted to have formed due to glacial scouring and transport of shelf sediments to the mouth of the Joides Trough, where slope failures and meltwater pulses remobilized this material downslope to the Central Basin. Dense shelf water formation is inferred to be most intense during interglacial periods, with reduced export from the Joides Trough during ice sheet advances. The study does not find any evidence for prolonged ice-sheet grounding in the outer Ross Sea since ~0.3 Ma, however, we conclude that the grounding line reached the outer shelf frequently between 0.3 and 1.2 Ma, supporting higher Antarctic ice volumes during glacial periods in this interval. • High-resolution sediment age modelling of Pleistocene Antarctic sediments • The WAIS has likely not been grounded in the outer Ross Sea since MIS 10. • Bottom water export from the Ross Sea is strongest during interglacial periods. [ABSTRACT FROM AUTHOR]

Reconstructing the advance and retreat of past ice sheets provides important long-term context for recent change(s) and enables us to better understand ice sheet responses to forcing mechanisms and external boundary conditions that regulate grounding line retreat. This study applies various radiocarbon dating techniques, guided by a detailed sedimentological analyses, to reconstruct the glacial history of Anvers-Hugo Trough (AHT), one of the largest bathymetric troughs on the western Antarctic Peninsula (WAP) shelf. Existing records from AHT indicate that the expanded Antarctic Peninsula Ice Sheet (APIS) advanced to, or close to, the continental shelf edge during the Last Glacial Maximum (LGM; 23-19 cal kyr BP [ = calibrated kiloyears before present]), with deglaciation of the outer shelf after ∼16.3 cal kyr BP. Our new chronological data show that the APIS had retreated to the middle shelf by ∼15.7 cal kyr BP. Over this 600-year interval, two large grounding-zone wedges (GZW) were deposited across the middle (GZW2) and inner shelf (GZW3), suggesting that their formation occurred on centennial rather than millennial timescales. Expanded sequences of sub-ice shelf sediments occur seaward of the inner GZW3, which suggests that the grounding line remained stationary for a prolonged period over the middle shelf. Grounding-line retreat rates indicate faster retreat across the outer to middle shelf compared to retreat across the middle to inner shelf. We suggest that variable retreat rates relate to the broad-scale morphology of the trough, which is characterised by a relatively smooth, retrograde seabed on the outer to middle shelf and rugged morphology with a locally landward shallowing bed and deep basin on the inner shelf. A slowdown in retreat rate could also have been promoted by convergent ice flow over the inner shelf and the availability of pinning points associated with bathymetric highs around Anvers Island and Hugo Island. • The deglacial history of Anvers-Hugo Trough is revealed by marine geological and geophysical data. • Application of multiple 14C dating methods allows reliable dating of ice sheet retreat. • Grounded ice had retreated to the mid-shelf by ∼15.7 cal kyr BP. • Retreat rates are controlled by the broad-scale morphology of the shelf. [ABSTRACT FROM AUTHOR]

• Application of the emulator CLISEMv1.0 to simulate the Antarctic ice sheet growth during the late Eocene up to the Oligocene. • Model evidence for short-lived continental-scale ice sheets prior to the Eocene-Oligocene transition. • Use of highly detailed CO 2 forcing close to the glaciation threshold. • Large dependency of the CO 2 threshold to glaciation on the bedrock topography. It is generally believed that a large scale Antarctic ice sheet formed at the Eocene-Oligocene transition (34.44-33.65 Ma). However, oxygen isotope excursions during the late Eocene (38-34 Ma) and geomorphic evidence of glacial erosion suggest that there were ephemeral continental scale glaciations before the Oi-1 event. Here, we investigate the Antarctic ice sheet evolution over a multi-million year timescale during the late Eocene up to the early Oligocene with the most recent estimates of carbon dioxide evolution over this time period and different bedrock elevation reconstructions. A novel ice sheet-climate modelling approach is applied where the Antarctic ice sheet model VUB-AISMPALEO is coupled to the emulated climate from HadSM3 using the coupler CLISEMv1.0. Our modelling results show that short-lived continental scale Antarctic glaciation might have occurred during the late Eocene when austral summer insolation reached a minimum in a narrow range of carbon dioxide concentrations. The Antarctic ice sheet first reached the coast in Prydz Bay and later in the Weddell Sea region, supporting the glaciomarine sediments dated prior to the EOT. [ABSTRACT FROM AUTHOR]

Sedimentation and bioturbation (the activity of benthic organisms) play an important role in organic matter degradation. The excess 230Th and 210Pb in a sediment core were used to evaluate the sedimentation, bioturbation and organic degradation processes in the Cosmonaut Sea, East Antarctica. Our results show that the sedimentation rate estimated from excess 230Th through the Constant Flux (CF) and Constant Flux and Constant Sedimentation (CFCS) models has changed in the past 200 ka. The mass accumulation and the linear sedimentation rates vary from 0.36 to 0.76 kg m-2 ka-1 and from 0.6 to 1.3 mm ka-1, which are significantly lower than the rates in other Antarctic seas. The stage III (120–202 ka), which corresponds to Marine Isotope Stage (MIS) 6 (glacial period), had the lowest sedimentation rate, indicating less sediment input by sea ice expansion. The bioturbation coefficient estimated by excess 210Pb is as low as 0.023 ± 0.003 cm2 a-1, showing inactive benthic activities. The average C/N ratio of organic matter is 7.2 ± 0.4, which is close to that of fresh organic matter and lower than the typical value of deep-sea sediments, indicating that organic matter is less degraded. The degradation rates of organic carbon and organic nitrogen estimated by the bio-diffusion model are 0.61 ka-1 and 0.29 ka-1, respectively, which are significantly lower than previously reported values for Southern Ocean sites. Despite the low sedimentation rate, low rates of bioturbation and inefficient organic matter degradation are conducive to the preservation of organic matter in sediments of the Cosmonaut Sea. ∙ The mass accumulation and linear sedimentation rates in the Cosmonaut Sea are low. ∙ The bioturbation coefficient in the Cosmonaut Sea estimated by excess 210Pb is as low as 0.023 cm2 a-1. ∙ Low rates of bioturbation and inefficient degradation are conducive to the preservation of organic matter in the Cosmonaut Sea sediments. [ABSTRACT FROM AUTHOR]

Nitrate (NO 3 −), an abundant aerosol in polar snow, is a complex environmental proxy to interpret owing to its diverse sources and susceptibility to post-depositional processes. During the last glacial period, when dust concentrations in the Antarctic ice were upto ~50 times than today, mineral dust appears to have a stabilizing effect on the NO 3 − concentration in snow. However, the mechanism leading to the stabilization remains unclear. Here, we present the new and highly resolved records of NO 3 − and non-sea salt calcium (nssCa2+, a proxy for mineral dust) from the Roosevelt Island Climate Evolution (RICE) ice core. We focus on the glacial period from 83 to 26 kilo years Before Present (ka BP). The data show a statistically significant correlation between NO 3 − and nssCa2+ over this period. To put our findings into a spatial context, we compare RICE data with existing records from east Antarctica (EPICA Dome C [EDC], Vostok and central Dome Fuji) and West Antarctica (West Antarctic Ice Sheet Divide Ice Core [WDC]). Spatial analysis suggests that nssCa2+ is contributing to the effective scavenging of NO 3 − from the atmosphere perhaps through the formation of calcium nitrate (Ca(NO 3) 2). The geographic pattern implies that the process of Ca(NO 3) 2 formation occurs during the long-distance transport of mineral dust from mid-latitude source regions by Southern Hemisphere Westerly Winds (SHWW). The data also suggest that the correlation observed at various Antarctic locations may depend on the level of dust reaching the sites from the mid-latitude sources. • A new Antarctic coastal record for mineral dust and nitrate for the last glacial. • Mineral dust-nitrate association is an Antarctic wide phenomenon during the glacial. • Mineral dust scavenges nitrate from the atmosphere. • Dust bound nitrate is dispersed to Antarctic atmosphere by westerly winds. • Scavenging efficiency increases when the atmospheric dust loading is high. [ABSTRACT FROM AUTHOR]

We report on the characterization of a thick sequence of pyroclastic deposits exposed on the summit area and flanks of Mount Melbourne volcano, in northern Victoria Land, Antarctica related to eruptions during the Late Glacial period. We provide a complete characterization of tephra deposits including mineralogy, single shard major- and trace-element glass compositions, and an 40Ar-39Ar age of feldspar crystals extracted from the deposit. The pyroclastic deposits are trachybasaltic to trachytic in composition and are interpreted to have resulted from four Strombolian/Vulcanian to sub-Plinian/Plinian eruptions. The younger and more intense sub-Plinian/Plinian eruption (our eruption 2) yielded an 40Ar-39Ar age of 13.5 ± 4.3 ka (±2σ). The study of Mount Melbourne proximal deposits provides significant new data for the reconstruction of the volcano eruptive history and a better assessment of the volcanic risk connected to a possible future eruption. We also explore geochemical correlations between Mount Melbourne proximal deposits and distal tephra layers recognized in ice cores and blue ice fields of East Antarctica. A good geochemical match exists between the composition of products from the trachytic sub-Plinian/Plinian eruption 2 and some tephra layers from Talos Dome and shards in Siple Dome which is also compatible in age (c. 9.3 ka) with our 40Ar-39Ar age determination. Our new insights into the volcanic history of Mount Melbourne and the new high-quality electron microprobe and trace element composition data on its proximal products will help improve future correlations and synchronization of tephra archives in the region. • New insights into the volcanic history of Mt. Melbourne, in the northern Victoria Land, Antarctica • Stratigraphy of pyroclastic deposits exposed in the summit area of the volcano • High-quality major and trace element glass compositions and a 40Ar-39Ar age • Four Strombolian/Vulcanian to Plinian eruptions were detected fed by trachybasaltic to trachytic magmas • Improved geochemical dataset for correlations of tephra archives in the region. [ABSTRACT FROM AUTHOR]

Knowledge regarding the response of the East Antarctic Ice Sheet to glacial–interglacial climatic cycles in the late Pleistocene is critical to understanding the global climate system and projections of future sea level rise. Here, we observed notable glacial–interglacial cyclicity in magnetic properties, bulk detrital Sr–Nd isotopes, and Fe/Ti ratios over the previous 530 kyr in three well-dated gravity cores from the continental rise offshore of Prydz Bay (East Antarctica). Our results show that Antarctic continental sources with more Ti-rich magnetite, less radiogenic epsilon neodymium (ε Nd), and higher Fe/Ti ratios were predominant during glacials in comparison with interglacials. Specifically, the ε Nd amplitude through MIS 11–5 differs from that in the remainder of the records, which is also expressed in the magnetic coercivity cycles with subdued patterns. Following source identification on the basis of the detrital Sr–Nd distribution, we recognize two main (rock type) sources and infer two types of ice drainage flow pattern ("flank" and "channelized"), which follow different pathways in the Lambert Glacier–Amery Ice Shelf system (LG-AISS). The first follows an eastern path connecting the Ingrid Christensen Coast (flank), while the second follows a central channel via the LG-AISS (channelized) during MIS 11–5. Regular dynamics on glacial–interglacial timescales, manifested by changes in magnetic coercivity, are closely related to the modeled Antarctic ice volume and ice sheet movement, in which the second channelized pathway during MIS 11–5 corresponds to a 340-kyr-long episode with contiguous warmer-than-present Antarctic interglacials (MIS 11, 9, 7, and 5). Our records thus provide the clearest evidence so far of variable patterns of ice sheet dynamics during the late Pleistocene in the Prydz Bay sector of East Antarctica, which coincided with similar variation of ice drainage during the late Miocene–early Pliocene at around 1.13 Ma (ODP188). Similar ice drainage changes in these two periods imply that major ice flow reconfiguration can be triggered repeatedly by abrupt changes from a stable warm period to a cold one. The presented data not only reveal glacial–interglacial cyclicity in ice sheet advance and retreat in the meridional direction, but also implicate latitudinal adjustment (lateral) within a thin elongated drainage basin of the LG-AISS. • Ti-rich and Ti-poor magnetite dominate glacial and interglacial terrigenous material respectively eroded by ice sheet. • Detrital Sr/Nd show two end members from Archean―paleoproterozoic and Meso-Neoproterozoic outcrops from Prydz Bay sector. • Amplitude changes of ε Nd during MIS 11―MIS 5 produce three-stage shifts in terrigenous sources and ice sheet patterns. • "Channel" and "flank" erosion patterns are postulated respectively for MIS 11―MIS 5 and the remainder the last 530 kyr. • The long period of warmth during MIS 11―MIS 5 might correspond to the long eccentricity controlled Antarctic ice volume. [ABSTRACT FROM AUTHOR]

Understanding the history of Antarctic glaciation is important for interpreting paleoclimatic changes and estimating the changes in climate, sea level, and ice volume in the future. Ice core studies of the East Antarctic Ice Sheet (EAIS) and marine sediment cores from the entire Ross Sea have employed numerous proxies to reconstruct the glacial history of the Antarctic region. However, the ice and marine core records can be biased because of their specific locations, such as the uppermost accumulation zone or the terminus of the ablation zone, thereby introducing significant uncertainties in ice modeling. In this study, we analyzed 34 new 10Be and 26Al samples from four benches that were glaciated in the past by David glacier and incorporate the present ice-free flat surfaces. We suggest that the David glacier experienced monotonic and stepwise vertical lowering along the flanks of Mt. Priestley since the early Pleistocene. The uppermost bedrock benches on Mt. Priestley were exposed at 1.77 ± 0.32 Ma, with no evidence of subsequent overriding by readvancing ice. At Mt. Priestley, the David glacier has been characterized by a cold-based regime since 1.77 Ma, with a denudation rate of only ∼16 cm/Ma, corresponding to the regional transition from warm to cold-based glaciation at 3.5 Ma. Simple exposure ages from two lower benches date to Marine Isotope Stage (MIS) 7 (234.1 ± 13.1 ka; 545 m asl) and MIS 4 (64.8 ± 13.7 ka; 222 m asl), suggesting that, since MIS 8, the overall lowering of glaciers has remained monotonic. The upper bench marks the lower limit of the MIS 8 glacial period and the upper limit of Penultimate Glacial Maximum (MIS 6), while the lower landform defines the upper limit of the last glacial period (MIS 4–2). The magnitude of Quaternary ice thinning at the David glacier was the highest (∼990 m) in the present terminal area (i.e., the most sensitive ablation zone), in contrast to the other outlet glaciers draining into the Terra Nova Bay, which experienced less ice lowering. The combination of the terrestrial (in situ 10Be and 26Al) and previous marine (authigenic 10Be) cosmogenic data used in our study document the history of lowering of the David glacier driven by climatic changes during the Pleistocene. Both deglaciation and glaciation were limited during the mid-Pleistocene transition (MPT) and prior to the mid-Bruhnes event (MBE), due to the prevailing cold and arid climate, whereas deglaciation was dominant during other warm periods. • 10Be &26Al, in combination with previous authigenic 10Beelucidate the glacial history of David glacier during the entire Quaternary period. • Experienced monotonic terrestrial vertical lowering with complex and multiple cycles of horizontal retreat–advance at its marine margin. • The greatest ice lowering along David glacier during the Quaternary (∼990 m) occurred at its present terminal region. • The ice surface elevation of the East Antarctic Ice Sheet was greater during the Pliocene than the Pleistocene. • Ice thickness was greater in MIS 8 than MIS 6 and the Global LGM. [ABSTRACT FROM AUTHOR]

• An Antarctic ice core provides new sulfur isotopes data during the last deglaciation. • Sulfur isotope ratio was negatively correlated with terrestrial contributions. • The data suggest enhanced contributions from terrestrial gypsum during the LGM. • A potential source area for gypsum is the high altitude area in the Atacama Desert. • Salts in deserts should be considered as a source for LGM sulfate aerosols. Chemical proxy data from ice cores provide information for understanding environmental changes. Despite large climate shifts, the flux of sulfate onto the ice in Antarctica has remained relatively stable over glacial-interglacial cycles. However, the mechanism behind the stable flux is controversial because of a lack of evidence for changes in multiple source emissions. Here, we present the sulfur isotopic record in the Antarctic Dome Fuji ice core, which provides a new constraint on the interpretation of sulfate aerosols. During the Last Glacial Maximum (LGM), the sulfur isotope ratio was depleted compared to that during the Holocene and was negatively correlated with terrestrial contributions. The isotope data suggest that the contributions from terrestrial gypsum were enhanced during the LGM. A potential source area for gypsum in the Antarctic ice core is the high-altitude region around the Atacama Desert, although other regions cannot be excluded. These results suggest that the salts in deserts should be considered a terrestrial source of Antarctic sulfate during the LGM. [ABSTRACT FROM AUTHOR]

Recently, devastating fires have caused social disruptions and huge economic losses. Understanding the relationship between natural fires and climate is helpful for predicting future fire activity. Here, we detected biomass burning biomarkers (levoglucosan (Lev), mannosan (Man) and galactosan (Gan)) in a sediment core RN-01 from East Antarctica, and reconstructed the Southern Hemisphere fire history for the past 15.6 kyr. Source analysis shows that the Lev in RN-01 is derived from a mixed Southern Hemisphere source, in which South America is generally the most important. Lev/Man ratios indicate that softwood dominates the burning, although the proportion changes over time. The reconstructed fire activities were more frequent during the late glacial (∼16-14 kyr BP and ∼13-11 kyr BP). Since the Holocene, the fire intensity showed an overall trend of decreasing. Precipitation, which was affected by the latitudinal shift of the Intertropical Convergence Zone (ITCZ) and the Southern Westerly Winds (SWW), plays an important role in the long-term change of fire activity since the late glacial period in the Southern Hemisphere. • The Southern Hemisphere fire history in the past 15.6 kyr were reconstructed through an Antarctic sediment core. • The vegetation type of burning was reconstructed, with a dominance of softwood. • The last deglaciation period has much more intensified fire activities than in Holocene. • Precipitation, which was affected by ITCZ and SWW, plays an important role in the long-term fire variation. [ABSTRACT FROM AUTHOR]

The repeated proximity of West Antarctic Ice Sheet (WAIS) ice to the eastern Ross Sea continental shelf break during past ice age cycles has been inferred to directly influence sedimentary processes occurring on the continental slope, such as turbidity current and debris flow activity; thus, the records of these processes can be used to study the past history of the WAIS. Ross Sea slope sediments may additionally provide an archive on the history and interplay of density-driven or geostrophic oceanic bottom currents with ice-sheet-driven depositional mechanisms. We investigate the upper 121 m of Hole U1525A, collected during International Ocean Discovery Program (IODP) Expedition 374 in 2018. Hole U1525A is located on the southwestern external levee of the Hillary Canyon (Ross Sea, Antarctica) and the depositional lobe of the nearby trough-mouth fan. Using core descriptions, grain size analysis, and physical properties datasets, we develop a lithofacies scheme that allows construction of a detailed depositional model and environmental history of past ice sheet-ocean interactions at the eastern Ross Sea continental shelf break/slope since ~2.4 Ma. The earliest Pleistocene interval (~2.4- ~ 1.4 Ma) represents a hemipelagic environment dominated by ice-rafting and reworking/deposition by relatively persistent bottom current activity. Finely interlaminated silty muds with ice-rafted debris (IRD) layers are interpreted as contourites. Between ~1.4 and ~0.8 Ma, geostrophic bottom current activity was weaker and turbiditic processes more common, likely related to the increased proximity of grounded ice at the shelf edge. Silty, normally-graded laminations with sharp bases may be the result of flow-stripped turbidity currents overbanking the canyon levee during periods when ice was grounded at or proximal to the shelf edge. A sandy, IRD- and foraminifera-bearing interval dated to ~1.18 Ma potentially reflects warmer oceanographic conditions and a period of stronger Antarctic Slope Current flow. This may have enhanced upwelling of warm Circumpolar Deep Water onto the shelf, leading to large-scale glacial retreat at that time. The thickest interval of turbidite interlamination was deposited after ~1 Ma, following the onset of the Mid-Pleistocene Transition, interpreted as a time when most ice sheets grew and glacial periods were longer and more extreme. Sedimentation after ~0.8 Ma was dominated by glacigenic debris flow deposition, as the trough mouth fan that dominates the eastern Ross Sea continental slope prograded and expanded over the site. These findings will help to improve estimations of WAIS ice extent in future Ross Sea shelf-based modelling studies, and provide a basis for more detailed analysis of the inception and growth of the WAIS under distinct oceanographic conditions. • A detailed analysis of Pleistocene sediments from IODP Expedition 374 Site U1525 • Three main intervals of deposition between: 2.4 Ma–1.4 Ma, 1.4 Ma–0.8 Ma and < 0.8 Ma • Depositional context for the Hillary Canyon and the Ross Sea trough-mouth fan • Sandy, foraminifera-bearing interval at ~1.18 Ma suggests ice sheet collapse • Ice grounded at shelf edge more often after 1 Ma, TMF prograded over Site U1525 [ABSTRACT FROM AUTHOR]

Il y a déjà plus d'un demi-siècle, les premiers sites paléolithiques étaient découverts dans l'île d'Hokkaïdo par les archéologues locaux. Cependant, l'étude du Paléolithique à Hokkaïdō n'en est qu'à ses débuts. Jusqu'à présent, nous n'avons découvert aucune trace d'activité, ni de fossile d' Homo erectus , ni d'Homme de Neandertal (Homo sapiens neandertalensis) dans la région concernée. Nous savons qu'à la fin du Pléistocène, l'homme moderne (Homo sapiens sapiens) faisait la conquête de tous les continents sauf de l'Antarctique. À cette période, l'un de ces groupes allait du continent asiatique à Hokkaïdō en passant par le pont terrestre formé par le mer alors asséché. La première vague humaine a dû se situer aux alentours d'un peu plus de 20 000 ans BP mais rien n'est encore avéré chronologiquement. Contre toute attente, ces premiers habitants ont laissé de nombreuses traces de leurs activités dans toute l'île d'Hokkaïdō. Cependant, cela pose de nombreux problèmes car les indices chronologiques et les preuves géologiques sont assez limités.. Malgré cela et dans ce contexte, la téphrachronologie joue un rôle important. Notamment, les éruptions du volcan Eniwa montrent les index primordiaux dans la partie centrale d'Hokkaïdō. Ces dépôts volcano-sédimentaires sont répandus dans plusieurs régions d'Hokkaïdō, ce qui permet de distinguer chronologiquement les plus anciennes industries lithiques des plus récentes. La plupart de ces industries lithiques du Paléolithique supérieur sont taillées principalement dans de l'obsidienne provenant de cette île, mais aussi dans le schiste argileux local. En ce qui concerne l'obsidienne utilisée, elle provient de quatre affleurements principaux. Au cours de l'époque préhistorique, cette roche éruptive était extraite en grande quantité et transportée sur de grande distance dans toute l'île. C'était une matière première de qualité très recherchée pour la fabrication des outils lithiques comme dans beaucoup de cas dans le monde. Situé au nord d'Hokkaïdō, l'affleurement d'obsidienne de Shirataki est le plus important. L'obsidienne provenant de Shirataki se retrouve souvent en abondance dans les sites situés dans un rayon de sept cents kilomètres au moins. L'étendue de la circulation géographique de cette obsidienne recouvre toute l'île d'Hokkaïdō, mais elle circulait également en dehors de cette île. Les préhistoriens d'Hokkaïdō ont distingué huit processus de technique de débitage lamellaire. Parmi eux, certains processus techniques n'existaient que dans une petite région alors que les autres processus techniques ont été largement observés parmi les groupes humains peuplant le continent asiatique. Pour le moment, notre étude ne comprend pas toutes les périodes du Paléolithique supérieur et nous n'avons pas pu encore proposer une chronologie achevée de cette région. La plus vieille industrie lithique se compose des outils typiques du Paléolithique supérieur. De même, dès le premier stade du Paléolithique supérieur, la technique du débitage lamellaire est connue, comme dans le site de Kashiwadaï-I. Le niveau archéologique de ce site correspond à la période la plus ancienne par rapport au dépôt volcano-sédimentaire d'Eniwa (En-a) qui est équivalent au Maximum glaciaire du Würm récent. L'étape suivante ou le deuxième stade se déroule après le dépôt mentionné et dont le site d'Osatsu-16présente les industries lithiques de cette période. Le troisième stade correspond à la période du Paléolithique supérieur final dont les industries lithiques ont des correspondances entre l'aube et le premier stade de la période Jômon. Il se caractérise par l'apparition de poterie. C'est ce qu'on appelle le Sub-néolithic-Culture dont il est, culturellement, un stade transitionnel tout en gardant des traits traditionnels fortement marqué du Paléolithique supérieur. Il se confirme que le dernier stade correspond à une courte période par rapport aux autres stades. Since the discovery of the first Paleolithic site in Hokkaido, we consider that the time in the half more than centuries already passed, and float today. However, our research is still a way. By today, we have not discovered the trace about a Pithecantropines (Homo erectus) and a Paleanthropic man (Homo sapiens neanderthalensis) at all in this region. We know that a Neanthropic man (Homo sapiens sapiens) dominated all the continents except Antarctica in the final time of the Pleistocene era. And they passed along the dried shoal which appeared to the north in the same time from the Asian Continent to the Island of Hokkaido, and reached it to this place. The first attainment time is an age which exceeds 20,000-years before a little from the present. We are not checking a fact which exceeds it you to be much. However, the habitants of these beginnings left the trace of the activity of them in large numbers, so that he was wonderful to inside of this island. The studies-of-prehistory research in Hokkaido has little proof of the natural science field concerned on age determination or chronology. This has serious restriction. However, the tephra-chronology of volcanic ashes has played the big role uniquely. The eruption of the Eniwa volcano of the Hokkaido central part is especially a very important index. This volcano blows off ash fall (En-a) in large quantities, and covered all large ranges. This deposited volcanic-ashes layer plays a big role to discernment of an old industry and a recent industry on the cultural chronology. The obsidian from this island and nearby hard shale was used for many industries of this Upper Paleolithic cultures as main materials. Although obsidians in the island where the different four outcrops are known well. This rock was mined in large quantities, and was carried in various places. As well as many examples in the world, we divided this rock, and the human beings of the prehistoric age were demanded for it, and it was often utilized. In it, especially the outcrop of Shirataki was located in the northern part of Hokkaido, and was very important. Large quantities of obsidian from Shirataki outcrop is discovered in a large number of Paleolithic sites within a segment 700 km in diameter at least. It covered the territory in Hokkaido and circulated further also except this island. This fact circulated as important trade materials on stone-tool fabrication among the human-beings groups from whom this island's every place differed. In this time, human beings' activity in Hokkaido is a clear proof, which was not isolated at all. As for the studies of the prehistorians of Hokkaido distinguish, the exception put the technical process of eight different microblade productions. The technical process of some of them was limited only to the specific narrow area. Or it is proved that other technical processes are widely connected with the human-beings group of the Asian Continent on the contrary. At present, our research grasps the whole second-half Paleolithic culture, and has not yet established the year system edited by locally complete. The oldest industry of this area composed the typical stone tool of second-half Paleolithic culture from the beginning, and was accompanied by the manufacturing technique of a braid and microblade. The feature is the example in which the ruins of Kashiwadai-I were most excellent. These ruins correspond at time older than deposition of the Eniwa volcano tephra. It is located at the chill time in the second half of a Würm glacial period. The second continuing step is an industry of succession newer than this volcano tephra. It is raised as an example with Ôsatsu-16 typical ruins etc. The third phase is an industry of the end term of second-half Paleolithic culture. It is simultaneously located in the dawn of Jōmon culture. The feature of this cultural aspect is a transitional cultural stage which earthenware appears and is called what is called "Sub-Neolithic-Culture". We can check having passed expansively, while the aspect of this last continues within a short period of time relatively. [ABSTRACT FROM AUTHOR]