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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]

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]

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 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]

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]

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]

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 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]

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]

When you are missing pieces from the jigsaw, the result may be attractive and even comprehensible, but it is incomplete. The conventional geological picture of the 'Traralgon Formation' in the Gippsland Basin includes a variety of ages, uses and concepts, and the formation's type section at Loy Yang has never been dated by palynology. The inclusion of new palynological data from bores at Loy Yang and elsewhere in the onshore part of the Gippsland Basin presents a more complete picture that reinterprets the age and distribution of the coal seams. The new data indicate that the Traralgon Formation coal seams in the Loy Yang area of the Latrobe Valley and the Lake Wellington Depression mostly comprise the youngest T0 coal seams, with Upper Nothofagidites asperus Zone (early Oligocene) ages. The Traralgon Formation coals in the Gormandale Syncline and Seaspray Depression, however, are mainly T1 and T2 coal seams of Middle and Lower Nothofagidites asperus Zone (late and middle Eocene) ages. The Rosedale Monocline, situated between the Latrobe Valley–Lake Wellington and Gormandale–Seaspray depressions, acted as a hinge that reversed movements at the Eocene–Oligocene boundary. Using quantitative palynology, the paleoclimates of the T0 seam are examined where it straddles the transition between the Eocene 'greenhouse' and the Oligocene 'icehouse'. In the Seaspray and Lake Wellington depressions below the T0 coal is an up to 150 m-thick regressive barrier sand of the upper Eocene Dutson Sand Member. The regression indicates that the climate transition began before end-Eocene and continued into the lower T0 coal. Mean annual temperatures (MATs) fell sharply from 16–17 °C to 14–16 °C to be ≤14 °C in the latest Eocene–earliest Oligocene. The lower T0 coal seams comprise a semi-continuous terrestrial record through the earliest Oligocene (the Oil glaciation event), marking the first significant glaciations in Antarctica. The upper part of T0 seam indicates a warmer, mesothermal climate, and MATs generally within the range of 14–16 °C. New palynology indicates that in the Loy Yang, Latrobe Valley, and the Lake Wellington depressions, the thickest Traralgon Formation coal seams have an Upper Nothofagidites asperus Zone (early Oligocene) age. In the Gormandale Syncline and Seaspray Depression the major coal seams are T1 and T2 with Middle and Lower Nothofagidites asperus Zone (late and middle Eocene) ages. Using quantitative palynology the transition between the Eocene 'greenhouse' and the Oligocene 'icehouse' began in the upper Eocene Dutson Sand Member and continued into the lower T0 coal. The upper part of T0 seam indicates a warmer, mesothermal climate, and mean annual temperatures generally within the range of 14–16 °C. [ABSTRACT FROM AUTHOR]

This study presents a 1:25,000 geomorphological map of the northern sector of Ulu Peninsula, James Ross Island, Antarctic Peninsula. The map covers an area of c. 250 km², and documents the landforms and surficial sediments of one of the largest ice-free areas in Antarctica, based on remote sensing and field-based mapping. The large-scale landscape features are determined by the underlying Cretaceous sedimentary and Neogene volcanic geology, which has been sculpted by overlying ice masses during glacial periods. Paraglacial and periglacial features are superimposed upon remnant glacial features, reflecting the post-glacial evolution of the landscape. The study area can be broadly separated into three geomorphological sectors, according to the dominant contemporary Earth-surface processes; specifically, a glacierised southern sector, a paraglacial-dominated eastern sector, and a periglacial-dominated central/northern sector. This map provides a basis for further interdisciplinary research, and insight into the potential future landscape evolution of other parts of the Antarctic Peninsula as the climate warms. [ABSTRACT FROM AUTHOR]

Orogenic crustal thickening leads to increased continental elevation and runoff into the oceans, but there are fundamental uncertainties in the temporal patterns of thickening through Earth history. U‐Pb age and trace element data in detrital zircons from Antarctica are consistent with recent global analyses suggesting two dominant peaks in average crustal thickness from ~2.6 to 2.0 Ga and ~0.8 to 0.5 Ga. Shifts in marine carbonate 87Sr/86Sr ratios show two primary peaks that post‐date these crustal thickness peaks, suggesting significant weathering and erosion of global continental relief. Both episodes correlate well with zircon trace element and isotope proxies indicating enhanced crustal and fluid input into subduction zone magmas. Increased crustal thickness correlates with increased passive margin abundance and overlaps with snowball Earth glaciations and atmospheric oxygenation, suggesting a causal link between continental rift‐drift phases and major transitions in Earth's atmospheric and oceanic evolution. [ABSTRACT FROM AUTHOR]

The East Antarctic Ice Sheet (EAIS) is the largest glacial system in the world, and the evolution history of the EAIS strongly affects global climate change. As one of the most extensive ice-free areas in coastal East Antarctica, the Larsemann Hills represent an important site for understanding the glacial evolution of East Antarctica. Generally, the last exposure process in the Larsemann Hills was considered to occur in the last glacial period. However, the initial time of the last exposure process in the Larsemann Hills remains unclear. This study presents the 10Be exposure ages of eight bedrock samples with glacial striae, which means that the original uneroded surfaces are preserved, from the Larsemann Hills and neighboring areas. The 10Be exposure ages ranging from 70.7 ± 4.7 to 13.5 ± 1.2 ka indicate that the Larsemann Hills have become ice-free since MIS4. The 10Be exposure ages with the characteristics of zonal distribution in the E–W direction and ages generally change from north to south, which reveals the combination of glacial retreat and topography differences. The activity of the ice sheet in the Larsemann Hills did not respond to the Last Glacial Maximum (LGM). In contrast, the deglaciation in the Larsemann Hills occurred as a diachronous process during the global last glacial periods, which began long before the LGM and lasted after the LGM. According to the exposure ages in the Larsemann Hills and the distance from the edge of the ice sheet, the average glacial retreat rate since MIS4 has been 71.57 m/ka. [ABSTRACT FROM AUTHOR]

Throughout the Quaternary, the continental‐based Antarctic ice sheets expanded and contracted repeatedly. Evidence suggests that during glacial maxima, grounded ice eliminated most benthic (bottom‐dwelling) fauna across the Antarctic continental shelf. However, paleontological and molecular evidence indicates most extant Antarctica benthic taxa have persisted in situ throughout the Quaternary. Where and how the Antarctic benthic fauna survived throughout repeated glacial maxima remain mostly hypothesised. If understood, this would provide valuable insights into the ecology and evolution of Southern Ocean biota over geological timescales. Here we synthesised and appraised recent studies and presented an approach to demonstrate how genetic data can be effective in identifying where and how Antarctic benthic fauna survived glacial periods. We first examined the geological and ecological evidence for how glacial periods influenced past species demography in order to provide testable frameworks for future studies. We outlined past ice‐free areas from Antarctic ice sheet reconstructions that could serve as glacial refugia and discussed how benthic fauna with pelagic or non‐pelagic dispersal strategies moved into and out of glacial refugia. We also reviewed current molecular studies and collated proposed locations of Southern Ocean glacial refugia on the continental shelf around Antarctica, in the deep sea, and around sub‐Antarctic islands. Interestingly, the proposed glacial refugia based on molecular data generally do not correspond to the ice‐free areas identified by Antarctic ice sheet reconstructions. The potential biases in sampling and in the choice of molecular markers in current literature are discussed, along with the future directions for employing testable frameworks and genomic methods in Southern Ocean molecular studies. Continued data syntheses will elucidate greater understanding of where and how Southern Ocean benthic fauna persisted throughout glacial periods and provide insights into their resilience against climate changes in the future. [ABSTRACT FROM AUTHOR]

We have summarized the results of studies of bottom rock material in Quaternary sediments in the polar seas of the Arctic, North Atlantic, and Antarctica, obtained by sieve washing on expeditions of the Shirshov Institute of Oceanology, Russian Academy of Sciences. We have compiled maps of the quantitative distribution of this material over water areas and created pie charts of the petrographic composition for various sites. A wide variety of petrographic types of rocks has been revealed, caused by their transport by glaciers, icebergs, and ice from glaciation centers on continents and islands. We have identified petrographic provinces based on the composition of the rock material and determined its sources. At the same time, great importance has been given to searching for marker rocks, making it possible to correlate the rock material of the seas with their land sources. [ABSTRACT FROM AUTHOR]

The Younger Dryas (YD), arguably the most widely studied millennialscale extreme climate event, was characterized by diverse hydroclimate shifts globally and severe cooling at high northern latitudes that abruptly punctuated the warming trend from the last glacial to the present interglacial. To date, a precise understanding of its trigger, propagation, and termination remains elusive. Here, we present speleothem oxygen-isotope data that, in concert with other proxy records, allow us to quantify the timing of the YD onset and termination at an unprecedented subcentennial temporal precision across the North Atlantic, Asian Monsoon-Westerlies, and South American Monsoon regions. Our analysis suggests that the onsets of YD in the North Atlantic (12,870 ± 30 B.P.) and the Asian Monsoon-Westerlies region are essentially synchronous within a few decades and lead the onset in Antarctica, implying a north-to-south climate signal propagation via both atmospheric (decadal-time scale) and oceanic (centennial-time scale) processes, similar to the Dansgaard– Oeschger events during the last glacial period. In contrast, the YD termination may have started first in Antarctica at ∼11,900 B.P., or perhaps even earlier in the western tropical Pacific, followed by the North Atlantic between ∼11,700 ± 40 and 11,610 ± 40 B.P. These observations suggest that the initial YD termination might have originated in the Southern Hemisphere and/or the tropical Pacific, indicating a Southern Hemisphere/tropics to North Atlantic–Asian Monsoon-Westerlies directionality of climatic recovery. [ABSTRACT FROM AUTHOR]

Environmental conditions were particularly severe during the Last Glacial Maximum, altering the distribution of the Southern Hemisphere biota, particularly at higher latitudes. The copepod Boeckella poppei is the only macroscopic continental invertebrate species known to be distributed today across the three main biogeographic regions in Antarctica as well as in southern South America. Signy Island (South Orkney Islands) is a unique location for the study of Antarctic freshwater ecosystems due to its location and geographic isolation; it contains 17 lakes in several low altitude catchments. We conducted phylogeographic and demographic analyses using the cox1 gene on 84 individuals of B. poppei from seven lakes across Signy Island. We recorded low levels of genetic diversity and a strong genetic differentiation signal between the eastern and western valleys within the island. Phylogeographic structure and demographic inference analyses suggested at least one asymmetrical dispersal event from west to east. Demographic inference detected a strong signal of population growth during the deglaciation process, which may have followed either (1) a strong genetic bottleneck due to a reduction in population size during the last glacial period, or (2) a founder effect associated with postglacial recolonization of Signy Island from elsewhere. The genetic architecture of this island's populations of B. poppei shows that historical events, rather than continuous dispersal events, likely played a major role in the species' current distribution. Finally, our study considers possible mechanisms for dispersal and colonization success of the most dominant species in the Antarctic freshwater community. [ABSTRACT FROM AUTHOR]

High-resolution seismic data from the Sabrina Coast continental shelf, East Antarctica, elucidate the Cenozoic evolution of the East Antarctic Ice Sheet. Detailed seismic stratigraphic and facies analysis reveal the Paleogene to earliest Pliocene glacial evolution of the Aurora Basin catchment, including at least 12 glacial expansions across the shelf indicated by erosional surfaces and chaotic acoustic character of strata. Differences in facies composition and seismic architecture reveal several periods of ice-free conditions succeeded by glacial expansions across the shelf. A deep (~100 m), undulating erosional surface suggests the initial appearance of grounded ice on the shelf. Following the initial ice expansion, the region experienced an interval of open-marine to ice-distal conditions, marked by an up to 200-m-thick sequence of stratified sediments. At least three stacked erosional surfaces reveal major cross-shelf glacial expansions of regional glaciers characterized by deep (up to ~120 m) channel systems associated with extensive subglacial meltwater. The seismic character of the sediments below the latest Miocene to earliest Pliocene regional unconformity indicates intervals of glacial retreat interrupted by advances of temperate, meltwater-rich glacial ice from the Aurora Basin catchment. Our results document the Paleogene to late Miocene glacial history of this climatically sensitive region of East Antarctica and provide an important paleoenvironmental context for future scientific drilling to constrain the regional climate and timing of Cenozoic glacial variability. [ABSTRACT FROM AUTHOR]

The results of mass balance observations of the ice dome and measurements of the active layer thickness on the Fildes Peninsula, King George (Waterloo) Island, Western Antarctica are presented for the period of 2007 to 2019. The dynamics of the main meteorological parameters affecting the active layer thickness is determined. The numerical experiments based on the mathematical model are performed to determine the effects of various parameters on the active layer thickness. The calculated and measured values of the active layer thickness are compared. The thermal instability of permafrost in the study area in some years with high (above the means) summer air temperature is demonstrated. The climate cooling which started in the region in the recent years has increased the number of years with the positive ice mass balance. However, the positive ice mass balance has not yet become a dominant factor against a background of the negative balance in the previous years. [ABSTRACT FROM AUTHOR]

Mount Achernar moraine is a terrestrial sediment archive that preserves a record of ice-sheet dynamics and climate over multiple glacial cycles. Similar records exist in other blue ice moraines elsewhere on the continent, but an understanding of how these moraines form is limited. We propose a model to explain the formation of extensive, coherent blue ice moraine sequences based on the integration of ground-penetrating radar (GPR) data with ice velocity and surface exposure ages. GPR transects (100 and 25 MHz) both perpendicular and parallel to moraine ridges at Mount Achernar reveal an internal structure defined by alternating relatively clean ice and steeply dipping debris bands extending to depth, and where visible, to the underlying bedrock surface. Sediment is carried to the surface from depth along these debris bands, and sublimates out of the ice, accumulating over time (>300 ka). The internal pattern of dipping reflectors, combined with increasing surface exposure ages, suggest sequential exposure of the sediment where ice and debris accretes laterally to form the moraine. Subsurface structure varies across the moraine and can be linked to changes in basal entrainment conditions. We speculate that higher concentrations of debris may have been entrained in the ice during colder glacial periods or entrained more proximal to the moraine sequence. [ABSTRACT FROM AUTHOR]

Briny groundwater is present below the extremely cold and dry surface of the McMurdo Dry Valleys and below the seafloor of the adjacent McMurdo Sound in Antarctica. The lack of reliable groundwater samples in the region, however, has long limited understanding of its origin, nature, and spatial distribution. In this regard, intergranular carbonate cements, widespread in subsurface Cenozoic strata and recently recognized as brine precipitates, provide an indirect means of solving these issues. This study examines the petrography and isotope geochemistry of intergranular aragonite cement phases that occur in subsurface Pliocene-Quaternary sedimentary sections that formed in the lower Taylor Valley (cores DVDP-10, -11) and in offshore McMurdo Sound (core AND-1B). Aragonite cement in the coastal Taylor Valley sections is characterized by very low δ18O values (−26.9 to −19.4‰ VPDB) compared to values in the offshore section (−12.5 to −2.7‰ VPDB). These differences are interpreted to reflect two settings for cryogenic brine formation, which produced isotopically distinct brines during Quaternary glaciation. In the coastal region, seawater-meltwater mixtures were isolated and cryogenically concentrated in an ice-dammed lake setting that formed in response to the expansion of the East and West Antarctic Ice Sheets into the lower Taylor Valley. In McMurdo Sound, cryogenic concentration of seawater occurred in a semi-isolated flexural trough that was deepened by lithospheric depression of volcanic edifices and the expanded West Antarctic Ice Sheet. Aragonite cement phases serve as excellent proxies for tracing the extents of subsurface brine bodies along the continental margin of Antarctica. Given the propensity for cryogenic brine formation in glaciomarine settings, the likelihood of brine cements in rock records from other analogous high-latitude, cold settings must not be overlooked. [ABSTRACT FROM AUTHOR]

Antarctica is isolated, surrounded by the Southern Ocean and has experienced extreme environmental conditions for millions of years, including during recent Pleistocene glacial maxima. How Antarctic terrestrial species might have survived these glaciations has been a topic of intense interest, yet many questions remain unanswered, particularly for Antarctica's invertebrate fauna. We examine whether genetic data from a widespread group of terrestrial invertebrates, springtails (Collembola, Isotomidae) of the genus Cryptopygus, show evidence for long‐term survival in glacial refugia along the Antarctic Peninsula. We use genome‐wide SNP analyses (via genotyping‐by‐sequencing, GBS) and mitochondrial data to examine population diversity and differentiation across more than 20 sites spanning >950 km on the Peninsula, and from islands both close to the Peninsula and up to ~1,900 km away. Population structure analysis indicates the presence of strong local clusters of diversity, and we infer that patterns represent a complex interplay of isolation in local refugia coupled with occasional successful long‐distance dispersal events. We identified wind and degree days as significant environmental drivers of genetic diversity, with windier and warmer sites hosting higher diversity. Thus, we infer that refugial areas along the Antarctic Peninsula have allowed populations of indigenous springtails to survive in situ throughout glacial periods. Despite the difficulties of dispersal in cold, desiccating conditions, Cryptopygus springtails on the Peninsula appear to have achieved multiple long‐distance colonization events, most likely through wind‐related dispersal events. [ABSTRACT FROM AUTHOR]

The last glacial period is punctuated by abrupt changes in Northern Hemisphere temperatures that are known as Dansgaard–Oeschger (DO) events. A striking and largely unexplained feature of DO events is an interhemispheric asymmetry characterized by cooling in Antarctica during periods of warming in Greenland and vice versa—the bipolar seesaw. Methane-synchronized ice core records indicate that the Southern Hemisphere lags the Northern Hemisphere by approximately 200 years. Here, we propose a mechanism that produces observed features of both the bipolar seesaw and the phasing of DO events. The spatial pattern of sea ice formation and melt in the Southern Ocean imposes a rigid constraint on where water masses are modified: waters are made denser near the coast where ice forms and waters are made lighter farther north where ice melts. This pattern, coupled to the tilt of density surfaces across the Southern Ocean and the stratification of the ocean basins, produces two modes of overturning corresponding to different bipolar seesaw states. We present evolution equations for a simplified ocean model that describes the transient adjustment of the basin stratification, the Southern Ocean surface density distribution, and the overturning strength as the ocean moves between these states in response to perturbations in North Atlantic Deep Water formation, which we take as a proxy for Greenland temperatures. Transitions between different overturning states occur over a multicentennial time scale, which is qualitatively consistent with the observed Southern Hemisphere lag. The volume of deep density layers varies inversely with the overturning strength, leading to significant changes in residence times. Evidence of these dynamics in more realistic circulation models is discussed. [ABSTRACT FROM AUTHOR]

• Abrupt mid-Holocene ice sheet thinning in western Weddell Sea Embayment since LGM. • At least 385 m of ice surface lowering revealed by in situ 14C exposure dating. • Glacial-geological data neither preclude nor mandate late Holocene ice thinning. The glacial history of the westernmost Weddell Sea sector of Antarctica since the Last Glacial Maximum is virtually unknown, and yet it has been identified as critical for improving reliability of glacio-isostatic adjustment models that are required to correct satellite-derived estimates of ice sheet mass balance. Better knowledge of the glacial history of this region is also important for validating ice sheet models that are used to predict future contribution of the Antarctic ice sheet to sea level rise. Here we present a new Holocene deglacial chronology from a site on the Lassiter Coast of the Antarctic Peninsula, which is situated in the western Weddell Sea sector. Samples from 12 erratic cobbles and 18 bedrock surfaces from a series of presently-exposed ridges were analysed for cosmogenic 10Be exposure dating, and a smaller suite of 7 bedrock samples for in situ 14C dating. The resulting 10Be ages are predominantly in the range 80–690 ka, whereas bedrock yielded much younger in situ 14C ages, in the range 6.0–7.5 ka for samples collected from 138–385 m above the modern ice surface. From these we infer that the ice sheet experienced a period of abrupt thinning over a short time interval (no more than 2700 years) in the mid-Holocene, resulting in lowering of its surface by at least 250 m. Any late Holocene change in ice sheet thickness — such as re-advance, postulated by several modelling studies — must lie below the present ice sheet surface. The substantial difference in exposure ages derived from 10Be and 14C dating for the same samples additionally implies ubiquitous 10Be inheritance acquired during ice-free periods prior to the last deglaciation, an interpretation that is consistent with our glacial-geomorphological field observations for former cold-based ice cover. The results of this study provide evidence for an episode of abrupt ice sheet surface lowering in the mid-Holocene, similar in rate, timing and magnitude to at least two other locations in Antarctica. [ABSTRACT FROM AUTHOR]

Outburst floods from subglacial lakes beneath the Antarctic Ice Sheet modulate ice-flow velocities over periods of months to years. Although subglacial lake drainage events have been observed from satellite-altimetric data, little is known about their role in the long-term evolution of ice-sheet basal hydrology. Here, we systematically map and model past water flow through an extensive area containing over 1000 subglacial channels and 19 former lake basins exposed on over 19 000 km 2 of seafloor by the retreat of Pine Island and Thwaites glaciers, West Antarctica. At 507 m wide and 43 m deep on average, the channels offshore of present-day Pine Island and Thwaites glaciers are approximately twice as deep, 3 times as wide, and cover an area over 400 times larger than the terrestrial meltwater channels comprising the Labyrinth in the Antarctic Dry Valleys. The channels incised into bedrock offshore of contemporary Pine Island and Thwaites glaciers would have been capable of accommodating discharges of up to 8.8×106 m 3 s -1. We suggest that the channels were formed by episodic discharges from subglacial lakes trapped during ice-sheet advance and retreat over multiple glacial periods. Our results document the widespread influence of episodic subglacial drainage events during past glacial periods, in particular beneath large ice streams similar to those that continue to dominate contemporary ice-sheet discharge. [ABSTRACT FROM AUTHOR]

Here we summarize the motivation and issues surrounding the responses of ice sheets and sea level to past climate warming as part of the PALeo constraints on SEA level rise (PALSEA) working group. Papers in this special issue of Quaternary Science Reviews focus on the timescale of glaciations during the late Pliocene, the magnitude of ice-sheet fluctuations and volume leading up to and during the last glacial maximum, the timing and persistence of ice-sheet impacts on deglacial and future relative sea-level change, and relative sea-level change during peak interglacial climate. A more dynamic cryosphere is noted under both late Pliocene and last glacial cycle climate conditions, while relative sea-level changes during the last deglaciation appear to correspond closely with individual ice-sheet deglaciation. Lastly, relative sea-level change during peak interglacial conditions may have fluctuated by as much as a meter, although the sources of such variability (Greenland, Antarctica or elsewhere) remain elusive. [ABSTRACT FROM AUTHOR]

Calculating cosmogenic-nuclide surface-exposure ages is critically dependent on a knowledge of the altitude of the sample site. Changes in altitude have occurred through time as a result of glacial isostatic adjustment (GIA), potentially altering local nuclide production rates and, therefore, surface-exposure ages. Here we assess the impact of GIA on surface-exposure dating by calculating global time-dependent production rates since the Last Glacial Maximum using surface elevations that were corrected and uncorrected for GIA. We find that the magnitude of the GIA effect is spatially and temporally variable. Nuclide production could be reduced by up to 50% in the interior of large ice masses (in North America, Scandinavia and West Antarctica) at times of maximum glacial isostatic depression. Although smaller, the effect is still significant at ice sheet margins, where nuclide production is reduced by >5% and potentially >10%, making exposure ages older in those areas. Away from the ice sheet margins, land surfaces can be isostatically elevated, which can increase nuclide production by >5% and, therefore, make exposure ages younger. Areas that were more recently exposed or that are distal to large ice masses will generally be less affected. Importantly, we find that the effect at the primary 10Be production calibration sites is <1%. Applying a GIA correction to surface-exposure data may help resolve mismatches between some chronologies, but not necessarily in all regions, implying that additional factors may need to be considered. Past atmospheric changes can amplify or reduce the impact of GIA on nuclide production, and the combined effects should be fully accounted for in the future. These time-dependent influences on surface-exposure dating have potentially important implications for interpreting chronologies and for using the data to constrain ice sheet models. • Glacial isostatic adjustment (GIA) can make exposure age estimates older or younger. • Nuclide production can be reduced by up to 50% from isostatic depression. • The GIA effect at the primary 10Be production rate calibration sites is negligible. • Correcting existing exposure datasets can make ages up to ∼2,500 years (15%) older. • Atmospheric changes may amplify or reduce the impact of GIA on exposure ages. [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]

This paper presents the first detailed paleoclimate reconstruction of the latest Antarctic isotope maximum (AIM4, ~ 33–29 ka cal. BP) at 52°S in continental southeastern Argentine Patagonia. High-resolution sedimentological and geochemical analyses of sediments from the maar lake Potrok Aike (PTA) reveal a decrease in the thickness of flood-induced turbidites and a series of wind burst deposits during AIM4, both pointing to increasingly drier conditions. This interpretation is also supported by a significant amount of runoff-driven micropumices incorporated within the sediments that suggests a lower lake level with canyons incising thick tephra deposits around the lake. Increased gustiness and/or dust availability in southeast Patagonia, together with intensified Antarctic circumpolar circulation in the Drake Passage, dust deposition in the Scotia Sea and in Antarctica ice shelf, are consistent with a southward shift of the Southern Westerly Winds (SWW) during the AIM4. In contrast to other warmer AIMs, the SWW during the AIM4 did not migrate far enough south to generate upwelling in the Southern Ocean and they did not reach 52°S in SE Patagonia, as revealed by unchanged values of the rock-magnetic proxy of wind intensity obtained from the same PTA core. Nevertheless, the SWW displacement during AIM4 imposed drier conditions at 52°S in southeast Patagonia likely by blocking precipitation from the Atlantic Ocean, in a way similar to modern seasonal variations and the other Antarctic warm events. [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]

Terrestrial cosmogenic nuclide exposure ages for the Wohlthat Massif (Antarctica), have previously been determined. This was done with 10 Be and 26 Al measurements by accelerator mass spectrometry (AMS) at the AMS facility at the ETH Zurich. In order to determine the extent to which the results from the Wohlthat Massif are of regional significance, additional samples were collected during the 2007 BGR-expedition “Queenmet”. Two of the Steingarden Nunataks (isolated mountain peaks) were chosen as sampling locations, approximately 100 km south-east of the Wohlthat Massif/Queen Maud Land, at the edge of the Polar Plateau. Quartz rich samples were collected at different elevations on the nunataks to reconstruct an elevation-dependent exposure history. The in situ produced cosmogenic nuclides 10 Be and 26 Al in these samples were measured by AMS. During sample processing the quartz separates were prepared by two different methods (Kohl and Nishiizumi, 1992, Altmaier, 2000) and measurements were performed at two different facilities (CologneAMS und Zurich AMS) to confirm the reproducibility of the results. The new results of rock surface exposure ages reveal that the exposure of the lower nunatak to cosmic radiation started between 0.65 and 1.1 Ma ago, while the more elevated regions of the second nunatak were apparently above the ice 3–4 Ma ago. [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]

According to paleontological data, large-scale, global glaciations occurred repeatedly over the history of Earth. Such glaciations unavoidably resulted in a sharp decrease in the number of habitats suitable for development of phototrophic microorganisms, which mostly require sunlight. Molecular data indicate that some groups of Antarctic phototrophic microorganisms emerged before formation of the Antarctic ice sheet (30-45 Ma) and probably survived the subsequent glaciation maxima. Analysis of the data on the present-day occurrence of phototrophs in Antarctica revealed the presence of liquid water in a habitat to be the key factor for survival of phototrophic communities. At negative air temperatures, this requirement may be met either in warmer microniches (0 to 30°C and higher) or in brines with freezing temperatures below zero (to −52°C). Development of phototrophic communities in such habitats may indicate the theoretical possibility of existence of the niches favoring growth of phototrophic microorganisms during Precambrian global glaciations. This possibility should be considered in paleontological reconstructions of development of life on Earth. [ABSTRACT FROM AUTHOR]

The late Eocene to Oligocene transition (EOT) witnessed a major ice advance on Antarctica. Because of the paucity of accessible outcrops and difficult drilling logistics, little is known about hydrological conditions in the Antarctic Peninsula during the late Eocene prior to the major ice advance. Here we study hydrological conditions with proxy evidence from marine sediment core NBP0602A-3C, adjacent to the tip of the Antarctic Peninsula, with sediments dated to 35.9 ± 1.1 Ma providing a snapshot of conditions prior to the EOT. We reconstruct conditions during the latest Eocene based on plant leaf wax hydrogen isotopic evidence ( δ D wax ) paired with previously-published evidence from pollen assemblages, and compared to climate model experiments simulating conditions before, during and after the transition. The pollen from late Eocene sediments of NBP0602A-3C indicate a Nothofagidites (southern beech) dominated landscape. In the same sediments, δ D wax values average − 202 ± 7 ‰ (1 σ , n = 22 ) for the C 28 n -alkanoic acid. Uncertainty around the appropriate net fractionation between water and wax ( ϵ wax / w ) provides the largest degree of uncertainty in paleoprecipitation δ D reconstructions and we therefore use two reasonable fractionations −100 and − 60 ‰ to constrain the likely range of average precipitation δ D values to between −113 and − 151 ‰ . Model experiments confirm that isotopic compositions show low sensitivity to temperature changes at the tip of the Antarctic Peninsula, in comparison to much larger changes in the continental interior. Across the interval sampled, a decline in pollen abundance from 10 5 to 10 3 gdw − 1 represents cooling and drying towards more tundra-like conditions. The 30‰ trend in δ D wax values towards more positive values can best be explained by smaller fractionations as the vegetation shifted from forest to tundra, with greater water stress. Model results are broadly consistent with the data and quantify the cooling and drying across the full EOT from ca. 7 to 2 °C and 700 to 600 mm a − 1 with an isotopic shift in δ D of only about − 15 ‰ at the tip of the Antarctic Peninsula. Pollen and leaf wax proxies reconstruct vegetation and hydrological conditions prior to the transition, and model experiments through the EOT provide proxy-groundtruthed quantification of terrestrial transformations. [ABSTRACT FROM AUTHOR]

Since the onset of glaciation following the Oligocene (30-28 Ma), the prevalence of increasingly cold conditions has shaped the evolution of the Antarctic biota. Two hypotheses, postglacial recruitment from extra-regional locations and in situ persistence, have been proposed to explain the biogeography of the contemporary species-poor terrestrial Antarctic biota. Bryophytes, which form a major group of the Antarctic flora, exhibit a strong, inherent ability to survive cold conditions but also have high long-distance dispersal capacities, which are compatible with both hypotheses. Here, we test these hypotheses by means of population genetic and phylogeographic analyses of the cosmopolitan moss Bryum argenteum. We find evidence for at least three independent colonisation events of the species in Antarctica. Ancestral area reconstruction coupled with molecular dating suggests colonisation times of the different Antarctic clades ranging from four million years for the oldest lineage to half a million years for the youngest lineage. This suggests multiple colonisation events of Antarctica by this species during several glacial cycles within the Pleistocene, Pliocene and possibly late Miocene. This is the first study to demonstrate in situ persistence of bryophytes in Antarctica throughout previous glaciations. [ABSTRACT FROM AUTHOR]

The Mi-1 glaciation (ca. 23 Ma), which marks the Oligocene-Miocene boundary, was an aberrant cooling event that led to a build-up of the Antarctic ice sheet, which reached the near-modern volume (or greater) from its ephemeral or partial existence. An increase of ~1‰ in the δ18O of benthic foraminifera during this interval has been attributed to the development of Antarctic ice sheets and deep-water cooling. Without definitive evidence, Northern Hemisphere (NH) glaciation has not been a material consideration for the δ18O increase. Here we investigate the interhemispheric temperature contrast during Mi-1, with the movement of the Intertropical Convergence Zone (ITCZ) at a site (10°31'N) in the East Pacific (Integrated Ocean Drilling Program Site U1333), to understand NH cooling and the possibility of NH glaciation. The measured 143Nd/144Nd, 87Sr/86Sr, and clay mineral compositions of eolian dust fractions indicate unequivocally the deposition of Asian dust during Mi-1, and of Central American and South American dust before and after Mi-1. This is attributed to the southward displacement of the ITCZ over Site U1333 during Mi-1. The ITCZ shifts toward the warmer hemisphere. Thus our results suggest that the cooling during Mi-1 was more significant in the NH than in the Southern Hemisphere, which underwent a sudden expansion of continental ice sheets. Our data call for a forcing mechanism to drive significant NH cooling during this episode. Based on the available data, we propose that the widespread growth of NH ice sheets and/or changes in the production of North Atlantic-origin deep water could be possible causes of the NH cooling at that time. [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]

• 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]