Search

One of Earth’s most fundamental climate shifts – the greenhouse-icehouse transition 34 Ma ago – initiated Antarctic ice-sheet build-up, influencing global climate until today. However, the extent of the ice sheet during the Early Oligocene Glacial Maximum (~33.7–33.2 Ma) that immediately followed this transition, a critical knowledge gap for assessing feedbacks between permanently glaciated areas and early Cenozoic global climate reorganization, is uncertain. Here, we present shallow-marine drilling data constraining earliest Oligocene environmental conditions on West Antarctica’s Pacific margin – a key region for understanding Antarctic ice sheet-evolution. These data indicate a cool-temperate environment, with mild ocean and air temperatures preventing West Antarctic Ice Sheet formation. Climate-ice sheet modeling corroborates a highly asymmetric Antarctic ice sheet, thereby revealing its differential regional response to past and future climatic change.

One of Earth’s most fundamental climate shifts – the greenhouse-icehouse transition 34 Ma ago – initiated Antarctic ice-sheet build-up, influencing global climate until today. However, the extent of the ice sheet during the Early Oligocene Glacial Maximum (~33.7–33.2 Ma) that immediately followed this transition, a critical knowledge gap for assessing feedbacks between permanently glaciated areas and early Cenozoic global climate reorganization, is uncertain. Here, we present shallow-marine drilling data constraining earliest Oligocene environmental conditions on West Antarctica’s Pacific margin – a key region for understanding Antarctic ice sheet-evolution. These data indicate a cool-temperate environment, with mild ocean and air temperatures preventing West Antarctic Ice Sheet formation. Climate-ice sheet modeling corroborates a highly asymmetric Antarctic ice sheet, thereby revealing its differential regional response to past and future climatic change.

One of Earth’s most fundamental climate shifts, the greenhouse-icehouse transition 34 million years ago, initiated Antarctic ice sheet buildup, influencing global climate until today. However, the extent of the ice sheet during the Early Oligocene Glacial Maximum (~33.7 to 33.2 million years ago) that immediately followed this transition—a critical knowledge gap for assessing feedbacks between permanently glaciated areas and early Cenozoic global climate reorganization—is uncertain. In this work, we present shallow-marine drilling data constraining earliest Oligocene environmental conditions on West Antarctica’s Pacific margin—a key region for understanding Antarctic ice sheet evolution. These data indicate a cool-temperate environment with mild ocean and air temperatures that prevented West Antarctic Ice Sheet formation. Climate–ice sheet modeling corroborates a highly asymmetric Antarctic ice sheet, thereby revealing its differential regional response to past and future climatic change. Editor’s summary Earth’s climate underwent a dramatic transition around 34 million years ago, when the Antarctic Ice Sheet first began to form, but the regional evolution of that ice sheet remains poorly defined. Klages et al . present data from marine sediments near West Antarctica showing that conditions there during the beginning of the Oligocene were mild and unfavorable to the growth of a permanent ice sheet. Model results based on those data suggest that the ice sheet in West Antarctica did not begin to form until 7 or 8 million years after the process began in East Antarctica.

Because ice shelves respond to climatic forcing over a range of time scales, from years to millennia, an understanding of their long-term history is critically needed for predicting their future evolution. We present the first detailed reconstruction of the Larsen C Ice Shelf (LCIS), eastern Antarctic Peninsula (AP), based on data from sediment cores recovered from below and in front of the ice shelf. Sedimentologic and chronologic information reveals that the grounding line (GL) of an expanded AP ice sheet had started its retreat from the midshelf prior to 17.7 ± 0.53 calibrated (cal.) kyr B.P., with the calving line following ~6 k.y. later. The GL had reached the inner shelf as early as 9.83 ± 0.85 cal. kyr B.P. Since ca. 7.3 ka, the ice shelf has undergone two phases of retreat but without collapse, indicating that the climatic limit of LCIS stability was not breached during the Holocene. Future collapse of the LCIS would therefore confirm that the magnitudes of both ice loss along the eastern AP and underlying climatic forcing are unprecedented during the past 11.5 k.y.

The Amundsen Sea sector of Antarctica has long been considered the most vulnerable part of the West Antarctic Ice Sheet (WAIS) because of the great water depth at the grounding line, a subglacial bed seafloor deepening toward the interior of the continent, and the absence of substantial ice shelves. Glaciers in this configuration are thought to be susceptible to rapid or runaway retreat. Ice flowing into the Amundsen Sea Embayment is undergoing the most rapid changes of any sector of the Antarctic ice sheets outside the Antarctic Peninsula, including substantial grounding-line retreat over recent decades, as observed from satellite data. Recent models suggest that a threshold leading to the collapse of WAIS in this sector may have been already crossed and that much of the ice sheet could be lost even under relatively moderate greenhouse gas emission scenarios. Drill cores from the Amundsen Sea provide tests of several key questions about controls on ice sheet stability. The cores offer a direct offshore record of glacial history in a sector that is exclusively influenced by ice draining the WAIS, which allows clear comparisons between the WAIS history and low-latitude climate records. Today, relatively warm (modified) Circumpolar Deep Water (CDW) is impinging onto the Amundsen Sea shelf and causing melting under ice shelves and at the grounding line of the WAIS in most places. Reconstructions of past CDW intrusions can assess the ties between warm water upwelling and large-scale changes in past grounding-line positions. Carrying out these reconstructions offshore from the drainage basin that currently has the most substantial negative mass balance of ice anywhere in Antarctica is thus of prime interest to future predictions. The scientific objectives for this expedition are built on hypotheses about WAIS dynamics and related paleoenvironmental and paleoclimatic conditions. The main objectives are To test the hypothesis that WAIS collapses occurred during the Neogene, QC 20230814

QC 20230814

QC 20230814

A multibarrel seabed drill rig was used for the first time to drill unconsolidated sediments and consolidated sedimentary rocks from an Antarctic shelf with core recoveries between 7% and 76%. We deployed the MARUM-MeBo70 drill device at nine drill sites in the Amundsen Sea Embayment. Three sites were located on the inner shelf of Pine Island Bay from which soft sediments, presumably deposited at high sedimentation rates in isolated small basins, were recovered from drill depths of up to 36 m below seafloor. Six sites were located on the middle shelf of the eastern and western embayment. Drilling at five of these sites recovered consolidated sediments and sedimentary rocks from dipping strata spanning ages from Cretaceous to Miocene. This report describes the initial coring results, the challenges posed by drifting icebergs and sea ice, and technical issues related to deployment of the MeBo70. We also present recommendations for similar future drilling campaigns on polar continental shelves.

In the scope of the International Polar Year 2007/2008, marine sediment cores were retrieved with RV Polarstern offshore the Prydz Bay to gain insight into land-ocean linkages of East Antarctic Ice Sheet (EAIS) dynamics, sea-ice formation, and regional palaeooceanography during the late Cenozoic. The scientific conception is based on the reconstruction of glaciomarine processes, comprising variations in ice-rafting, ice-shelf dynamics, and coastal bottom-water productivity. From our oldest sediment record, reaching back to 4.0 Ma, the results suggest a persistent presence of the EAIS in the Prydz Bay area during that time. The strongest glacial influence in the adjacent ocean appeared around the Plio-/Pleistocene boundary and during the mid-Pleistocene, consistent with maximum glaciation in the hinterland. The EAIS also fluctuated at glacial-interglacial timescales, documented by repeated stages of sediment reworking along the continental slope, prior to interglacials. The most apparent glacial retreat during the late Pleistocene took place after climate termination II, some 130 kyr ago. Another postglacial retreat event is evident from the inner shelf and commenced around 12 ka BP in agreement with ice shrinkage in adjacent onshore regions and global sea-level rise towards the Holocene. The variability of bottom-water formation in coastal polynyas reveals strong affinities to climate change that controls sea-ice extension. Strongest bottom-water activity apparently is related to intermediate interglacial stages, while it diminishes during both glacial stages and peak warmth. During glacial stages the permanent presence of near-shore sea-ice prevents the formation of polynyas, while during very warm stages the seasonal waxing and waning of sea ice is reduced and retards the brine-release effect needed for dense-water formation. The latter phenomenon in conjunction with glacial retreat was well expressed during climate termination II, which is also documented as an e

The Prydz Bay represents the third largest shelf area in Antarctica and is bounded to the south by the outlet of Lambert Glacier. The latter drains about 20 % of the East Antarctic Ice Sheet. Fluctuations in the extent and configuration of shelf ice and sea ice are known to be of wide influence on bottom-water formation in Antarctica. They are thus of global impact as Antarctic Bottom Water (AABW) is a driving force of Thermohaline Circulation. We apply sedimentological, mineralogical and geochemical methods on sediment cores retrieved from Prydz Bay, MacRobertson Shelf, the continental slope off MacRobertson Land, and from the East Kerguelen Drift deposit to reconstruct past variations in the formation of bottom-water and calving of icebergs.A depth transect of sediment cores from the continental slope off MacRobertson Land enables us to distinguish between periods of contourite and/or turbidity current activity and ice-rafting events. We use this information to draw conclusions on the advance and retreat of ice shelves and to deduce the glacial history in the Prydz Bay hinterland during the Pleistocene. Dating of the sediment records was done with the help of palaeomagnetics and diatom stratigraphy. Though interpretation of the sediment records is complicated by hiatuses and difficulties in age determination we identified two major phases of glacial retreat within the last 1.3 Ma. These episodes coincide with results from a drill hole through Prydz Mouth Fan and with exposure age data from Prince Charles Mountains derived from cosmogenic nuclides. The first and obviously very strong glacial retreat took place between ~1.0 - 0.76 Ma, beginning in the time of Jaramillo palaeomagnetic reversal and pronounced interglacial MIS 31. A later retreat started about 120 ka ago after the pronounced interglacial MIS 5.5. Possible changes in the mineralogy of ice-rafted material with respect to the earlier glacial regression tentatively hint to shifts in the provenance of IRD.

Modern global warming is likely to cause future melting of Earth's polar ice sheets that may result in dramatic sea-level rise. A possible collapse of the West Antarctic Ice Sheet (WAIS) alone, which is considered highly vulnerable as it is mainly based below sea level, may raise global sea level by up to 5-6 m. Despite the importance of the WAIS for changes in global sea level, its response to the glacial-interglacial cycles of the Quaternary is poorly constrained. Moreover, the geological evidence for the disintegration of the WAIS at some time within the last ca. 750 kyr, possibly during Marine Isotope Stage (MIS) 11 (424-374 ka), is ambiguous. Here we present physical properties, palaeomagnetic, geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the West Antarctic continental margin in the Amundsen Sea and spans more than the last 1 Myr. Within the sedimentary sequence, proxies for biological productivity (such as biogenic opal and the barium/aluminum ratio) and the supply of lithogenic detritus from the West Antarctic hinterland (such as ice-rafted debris and clay minerals) exhibit cyclic fluctuations in accordance with the glacial-interglacial cycles of the Quaternary. A prominent depositional anomaly spans MIS 15-MIS 13 (621-478 ka). The proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single, prolonged interglacial period. Even though no proxy suggests environmental conditions much different from today, we conclude that, if the WAIS collapsed during the last 800 kyr, then MIS 15-MIS 13 was the most likely time period. Apparently, the duration rather than the strength of interglacial conditions was the crucial factor for the WAIS drawdown. A comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout MIS 15-MIS 13. Some of these anomali

The Lambert Graben-Amery Ice Shelf system is one of the world's largest outlet glaciers, draining about 20% of the East Antarctic Ice Sheet. It is an important feature for the global water budget and for the production of dense Antarctic Bottom Water, which contributes to the global Thermohaline Circulation. On the basis of environmental proxy data, inferred from sedimentological, mineralogical, and geochemical studies, the response of the glacial drainage system to climate changes in the past is investigated. Sediment cores from a depth transect down the continental slope off MacRobertson Land cover the time-span of the last one million years, revealed from palaeomagnetic data. At least three lithofacies units can be distinguished and related to different conditions of the depositional environment: (1) a massive sediment facies with a high content of sand and gravel, and a heavy-mineral assemblage dominated by hornblende, points to strong input of ice- rafted material, advantaged by open-water conditions and prolonged iceberg calving in Prydz Bay; (2) a lithofacies characterized by sand- and silt stringers in combination with conspicuous presence of sediment clasts, indicating sediment reworking and bulldozing over the shelf edge, and sediment dispersal to the deep by turbidity currents during times of increased ice-sheet mobility; (3) a clayey-silty laminite facies that captivates through a low amount of ice-rafted debris, suggesting stable glacial conditions and the activity of contourite currents. The longterm trend reveals the dominance of the massive sediment facies between 1000 and 650 ka and since 100 ka, while the interval in between is mostly characterized by the laminite facies. Apparently, downcore changes in lithofacies are hard to correlate with shortterm glacial-interglacial climate stages. Sediment cores from the Prydz Bay shelf and the MacRobertson shelf document the Holocene environmental history. Grain-size data of a sediment core recovered from M