Bottom currents, sedimentation and ice-sheet retreat facies successions on the Mac Robertson shelf, East Antarctica

Stratigraphic information concerning the retreat of the Antarctic ice sheet from the continental shelf after the Last Glacial Maximum is
reviewed and compared with new results from a shelf valley off Mac. Robertson Land, East Antarctica. Radiocarbon dates and detailed
lithostratigraphic logs indicate that the onset of open-marine conditions over shallow shelfbanks «200 m water depth) was achieved prior
to 7000 yr BP and over deep (~l 000 m) middle to oliter shelf valleys, open-marine conditions were achieved prior to 5400 yr BP.
Radiocarbon dating of bulk-organic carbon in some diatom oozes by the AMS method demonstrates problems of contamination. Jurassic
pollen, spores and organic matter have been eroded and incorporated into Holocene diatom ooze, causing anomalously old 14C dates (e.g.
one surface age of7084 ± 86 yr BP was determined). This problem may arise at other locations around East Antarctica where older strata
outcrop on the seafloor.

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Late quaternary history of sedimentation on the Mac. Robertson Shelf, East Antarctica: Problems with 14C-Dating of marine sediment cores

The future behaviour of the Antarctic ice sheet depends to some extent on its current state of balance and its past history. The past history is primarily influenced by global climate changes, with some small amount of local feedback, and by sea-level changes generated primarily by the Northern Hemisphere ice-sheet changes, again with a small amount of feedback from the Antarctic ice sheet. An ice-sheet model which includes ice shelves has been used to model the Antarctic region and the whole Northern Hemisphere high-latitude region through the last ice-age cycle. For the climate forcing, the results from the global energy-balance model of Budd and Rayner (1990) are used. These are based on the Earth's orbital radiation changes with ice-sheet albedo feedback. Additional sensitivity studies are carried out for the amplitudes of the derived temperature changes and for changes in precipitation over the ice-sheets. For the Antarctic snow-accumulation changes, the results from the Voslok ice core are used with proportional changes over the rest of the ice sheet. For the sea-level variations, the results generated by the Northern Hemisphere ice-sheet changes provide the primary forcing, but account is also taken of the feedback effects from bed response under changing ice and ocean loading and from the Antarctic changes. The results of the modelling provide a wide range of features for comparison with observations, such as the margins of maximum ice extent. For the Northern Hemisphere the results indicate that the peak mean temperature shift required for the ice-edge region is about -12°C, whereas outside the ice-sheet region this change is smaller but over the ice sheets it is larger. For the Antarctic region during the ice age the interior region decreases in thickness, due to lower accumulation, while the grounding-edge region expands and thickens due to the sea-level lowering. As a result, the derived present state of balance shows a positive region over most of inland East Antarctica, whereas coastal regions tend to be nearer to balance, with some slightly negative regions around some of the large ice shelves and coastal ice streams which are still adjusting slowly to the post-ice-age changes of sea level and accumulation rates.

/pdf/modelling-the-antarctic-and-northern-hemisphere-ice-sheet-1dpvmabyne.pdf

Modelling the Antarctic and Northern Hemisphere ice-sheet changes with global climate through the glacial cycle

This paper revises recent studies [1-7] on paleoclimatic reconstructions from borehole thermometry at Vostok (East Antarctica), using more precise or complete, ice-core and environmental data. The principles of a model for heat transfer and ice flow are described. Three sequential possible steps of data processing are considered: 1) inverse reconstruction of the dominant (metronomic) part of the past orbitally driven temperature variations on the glacier surface from the borehole temperature profile; 2) correlation of the main climatic events on the smoothed ice-core isotope record with those on the geophysical metronome resulting in the ice age depth relationship; 3) calibration of the transfer function converting the isotopic content measurements to past surface temperatures. Glaciological and paleoclimatological implications of the results are discussed.

/pdf/paleoclimatic-reconstructions-based-on-borehole-temperature-3yczbtva1r.pdf

Paleoclimatic reconstructions based on borehole temperature measurements in ice sheets : possibilities and limitations

Retreat History of the Gerlache‐Boyd Ice Stream, Northern Antarctic Peninsula: An Ultra‐High Resolution Acoustic Study of the Deglacial and Post‐Glacial Sediment Drape

A three dimensional ice sheet model and a global energy balance climate model have been used to investigate the evolution of ice and climate changes through the ice ages. Sensitivity studies give an indication of the conditions required for the growth and decay of the ice sheets. Time series simulations in response to orbital forcing show the dominance of the ice sheets in the climate system converting seasonal and latitudinal variations into annual and global changes but with a large phase shift. Explicit calculations of phase differences show a sequence of leads and lags through July radiation, July temperature, ice area and annual mean temperature, ice volume and sea level, ocean δ 180, January temperature, January radiation and finally bedrock depression. The recognition of these phase shifts, caused primarily by the slow ice sheet response and feedback, may assist the interpretation of phase differences observed in proxy paleorecords.

Modelling Ice Sheet and Climate Changes through the Ice Ages

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W. F. Budd

Papers

Modelling Ice Sheet and Climate Changes through the Ice Ages

Global modelling of climate and ice sheets