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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]

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]

• 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]

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]

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]

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]

During the last interglaciation (LIG; ∼129–116 ka), global mean sea level (GMSL) was 6–9 m above present. However, the source, or sources, of the higher-than-present sea level are only partially confirmed with far fewer geologic constraints than GMSL itself. Because of modest LIG Greenland Ice-Sheet retreat that raised sea level by < 2.5 m, Antarctic ice sheets are hypothesized to have contributed significantly to the LIG GMSL highstand, but direct evidence is limited. Here we infer ice-sheet presence or absence on West Antarctica and the Antarctic Peninsula using sediment geochemistry in the Bellingshausen Sea at Ocean Drilling Program (ODP) Site 1096. In particular, a combination of Sr-Nd-Pb isotopes and trace-element ratios allows differentiation between silt sourced from West Antarctica and the Antarctic Peninsula. From the Holocene (<11.7 ka) back through Marine Isotope Stage (MIS) 5d (∼116 ka), we find in ∼50% of our samples glacially eroded silt sourced from under the West Antarctic Ice Sheet that was transported to the Bellingshausen Sea in the Antarctic Circumpolar Current, in addition to silt sourced from under the proximal Antarctic Peninsula Ice Sheet. However, West Antarctic-sourced silt is absent during the LIG (MIS 5e) when only Antarctic Peninsula-sourced silt was deposited at ODP Site 1096. This lack of West Antarctic-sourced silt is consistent with the two ice-core constraints on West Antarctic Ice Sheet LIG size, which combined with our record point towards the absence of the West Antarctic Ice Sheet during the LIG. We therefore provide the first marine-based sedimentary evidence that supports West Antarctic Ice-Sheet absence during the LIG. • The Bellingshausen Sea contains West Antarctic silt during the last glacial cycle. • The Bellingshausen Sea lacks West Antarctic silt during the last interglaciation. • West Antarctic last-interglacial deglaciation would explain its silt absence. [ABSTRACT FROM AUTHOR]

Reconstructing past ice-sheet surface changes is key to testing and improving ice-sheet models. Data constraining the past behaviour of the East Antarctic Ice Sheet are sparse, limiting our understanding of its response to past, present and future climate change. Here, we report the first cosmogenic multi-nuclide (10Be, 26Al, 36Cl) data from bedrock and erratics on nunataks along the Jutulstraumen and Penck Trough ice streams in western Dronning Maud Land, East Antarctica. Spanning elevations between 741 and 2394 m above sea level, the samples have apparent exposure ages between 2 ka and 5 Ma. The highest-elevation bedrock sample indicates (near-) continuous minimum exposure since the Pliocene, with a low apparent erosion rate of 0.15 ± 0.03 m Ma−1, which is similar to results from eastern Dronning Maud Land. In contrast to studies in eastern Dronning Maud Land, however, our data show clear indications of a thicker-than-present ice sheet within the last glacial cycle, with a thinning of ∼35–120 m during the Holocene (∼2–11 ka). Difficulties in separating suitable amounts of quartz from the often quartz-poor rock-types in the area, and cosmogenic nuclides inherited from exposure prior to the last deglaciation, prevented robust thinning estimates from elevational profiles. Nevertheless, the results clearly demonstrate ice-surface fluctuations of several hundred meters between the current grounding line and the edge of the polar plateau for the last glacial cycle, a constraint that should be considered in future ice-sheet model simulations. • Cosmogenic 26Al, 10Be, and 36Cl constrain past EAIS dynamics in Dronning Maud Land. • EAIS in western DML was at least 100–200 m thicker than present within last 25 ka. • EAIS in western DML was at least 150–300 m thicker within the last glacial cycle. • Ice-sheet thinning ∼35–120 m towards present ice sheet surface during the Holocene. • Short duration of Pleistocene ice covers >200 m above regional ice at Borgmassivet. [ABSTRACT FROM AUTHOR]

• Deglacial history of Pope Glacier reconstructed using surface exposure dating. • 560 m of early Holocene thinning at an average rate of 0.13 ± 0.09/0.04 m yr−1. • Thinning coincides with enhanced upwelling of warm water onto continental shelf. • Reduction in ice shelf buttressing may have triggered widespread glacier thinning. The Amundsen Sea sector of the Antarctic ice sheet presently dominates the contribution from Antarctica to sea level rise. Several large ice streams that currently drain the sector have experienced rapid flow acceleration, grounding line retreat and thinning during the past few decades. However, little is known of their longer-term – millennial-scale – retreat history, despite the reliance of several ice sheet and glacial-isostatic adjustment models on such data for improving sea level prediction from this critical region. This study investigates the timing and extent of surface lowering of one of those ice streams, Pope Glacier, since the Last Glacial Maximum (LGM), using glacial-geological evidence for former ice cover. We present a new deglacial chronology for the glacier, derived from surface exposure dating of glacially-deposited cobbles and ice-scoured bedrock from Mount Murphy and its surrounding peaks. Cosmogenic 10Be exposure ages from 44 erratic cobbles and 5 bedrock samples, and in situ 14C exposure ages from one erratic and 8 bedrock samples are predominantly in the range 5.5-16 ka. Although 10Be inheritance from prior exposure is prevalent in some erratics and probably all bedrock samples, none of the ages pre-date the LGM. From these results we infer that the surface of Pope Glacier lowered by 560 m during the early- to mid-Holocene (9-6 ka), at an average rate of 0.13 ± 0.09/0.04 m yr−1. The lowering coincided with a period of enhanced upwelling of warm Circumpolar Deep Water onto the continental shelf in the region. A reduction in buttressing − facilitated by such upwelling − by an ice shelf that is thought to have spanned the embayment until 10.6 cal kyr BP could have triggered simultaneous early Holocene thinning of Pope Glacier and glaciers elsewhere in the Amundsen Sea Embayment. [ABSTRACT FROM AUTHOR]