GPS Rates of Vertical Bedrock Motion Suggest Late Holocene Ice-Sheet Readvance in a Critical Sector of East Antarctica

We investigate present-day bedrock vertical motion using new GPS timeseries from the Totten-Denman glacier region of East Antarctica (∼77-120°E) where models of glacial isostatic adjustment (GIA) disagree, glaciers are likely losing mass, and few data constraints on GIA exist. We show that varying surface mass balance loading (SMBL) is a dominant signal, contributing random-walk-like noise to GPS timeseries across Antarctica. In the study region, it induces site velocity biases of up to ∼+1 mm/yr over 2010-2020. After correcting for SMBL displacement and GPS common mode error, subsidence is evident at all sites aside from the Totten Glacier region where uplift is ∼1.5 mm/yr. Uplift near the Totten Glacier is consistent with late Holocene ice retreat while the widespread subsidence further west suggests possible late Holocene readvance of the region’s ice sheet, in broad agreement with limited glacial geological data and highlighting the need for sampling beneath the current ice sheet

Holocene glacier fluctuations and environmental changes in sub-Antarctic South Georgia inferred from a sediment record from a coastal inlet

The sub-Antarctic island of South Georgia provides terrestrial and coastal marine records of climate variability, which are crucial for the understanding of the drivers of Holocene climate changes in the sub-Antarctic region. Here we investigate a sediment core (Co1305) from a coastal inlet on South Georgia using elemental, lipid biomarker, diatom and stable isotope data to infer changes in environmental conditions and to constrain the timing of Late glacial and Holocene glacier fluctuations. Due to the scarcity of terrestrial macro-fossils and relict organic matter in the sediments, age control was obtained by compound-specific radiocarbon dating of mostly marine derived n-C16 fatty acids. A basal till layer recovered in Co1305 was likely deposited during an advance of local glaciers during the Antarctic cold eversal. After glacier retreat an oligotrophic lake occupied the site, which transitioned to a marine inlet around 8.0±0.9 ka due to relative sea level rise. From 7.0±0.6 to 4.0±0.4 ka reduced vegetation coverage in the catchment as well as high siliciclastic input and deposition of ice rafted debris indicate glacier advances in the terrestrial catchment and likely in the adjacent fjord. A second, less extensive period of glacier advances occurred in the late Holocene, after 1.8±0.3 ka

A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum

A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20ka, 15ka, 10ka and 5ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorit. © 2014 The Authors

Cenozoic landscape and ice drainage evolution in the Lambert Glacier-Amery Ice Shelf system

Landforms and sediments in the Prince Charles Mountains record the timing and magnitude of Cenozoic palaeotopographic changes in the Lambert Glacier-Amery Ice Shelf system. A review of geomorphic and sedimentological evidence indicates that considerable (>1-2 km) glacial incision into a pre-glacial palaeosurface occurred along the major outlet glaciers during the Cenozoic. This erosion was in turn the likely driver for uplift that averaged c. 50 m/Ma along the flank of the Amery Ice Shelf since at least the mid-Miocene Epoch. The volume of eroded material is an order of magnitude greater than the quantity of sediment presently preserved in Prydz Bay, suggesting considerable export of Cenozoic sediment offthe continental shelf. The magnitude of erosion recorded in the Prince Charles Mountains is sufficient to have focussed Cenozoic ice-drainage patterns, but was too slow to have driven Quaternary changes in ice volume.15 page(s

Late Quaternary glacial history constrains glacio-isostatic rebound in Enderby Land, East Antarctica

Measurements of the loss or gain of ice mass from large ice sheets are presently achieved through satellite-based techniques such as GRACE (Gravity Recovery and Climate Experiment). The accuracy of these satellite-based measurements to changes in modern ice sheet mass depends on our knowledge of present-day glacio-isostatic crustal uplift rates caused by past ice sheet changes. To improve models of glacio-isostatic rebound in East Antarctica, we investigated ice histories along Rayner Glacier, Enderby Land, and a little explored sector of the ice sheet where GRACE data had suggested significant mass gain during the last decade. Observations from a recent glacial geomorphic reconnaissance coupled with cosmogenic nuclide dating indicate that in the lower part of the Rayner Glacier, Enderby Land, ice heights lowered by at least 300 m and the calving margin retreated by at least 10 km in the early Holocene (~6 to 9 ka B.P.). The magnitude and timing of deglaciation are consistent with ice histories used to model the postglacial rebound corrections for present-day GRACE mass trends. These observations strengthen the body of evidence that suggests ice mass gain in Enderby Land is presently partly offsetting mass loss in other parts of Antarctica.© 2014, American Geophysical Union

Cosmogenic nuclide evidence for enhanced sensitivity of an East Antarctic ice stream to change during the last deglaciation

Glacial sediments from the Prince Charles Mountains, East Antarctica, record late Pleistocene ice thickness variability in the Lambert Glacier-Amery Ice Shelf system, one of the world's largest ice drainages. A former glacial limit, demarcated by minimally weathered deposits, follows a concave longitudinal profile, indicating a zone of strong ice streaming through the northernmost 500 km of the Lambert Graben. In situ ¹⁰Be and ²⁶Al exposure ages from these relatively unweathered deposits indicate that the most recent phase of ice lowering occurred between ca. 18 and 8 ka, preceding by as many as 6 k.y. the deglaciation of adjacent coastal regions. Earlier onset of deglaciation in an area of strong ice streaming suggests a heightened sensitivity of the East Antarctic Ice Sheet to climate and sea-level changes following the Last Glacial Maximum than previously recognized.4 page(s

Glacial and periglacial history of the southern Prince Charles Mountains, East Antarctica

Field investigations into glacial sediments and landforms in the southern Prince Charles Mountains reveal at least four major phases of deposition. The oldest, which is a thick succession of mud-rich sediments on the summit surfaces, is a potential correlative of the mid-late Cenozoic Pagodroma Group. The next three are a series of thin, sandy diamict drapes across the massifs. The first phase of thin diamicts records a glacial expansion that inundated all of the 2000 m high nunataks, with weathering characteristics suggesting an early-mid Pleistocene age. The second phase records an ice height increase of ?800 m near the modern grounding line. Sediments from this phase are relatively unweathered, and depositional landforms indicate deposition probably terminated during the short warm phase that occurred between 11 and 9.5 ka BP. The third and final phase indicates minor readvance since this time.8 page(s