LATE CENOZOIC GLACIAL HISTORY OF THE ROSS EMBAYMENT, ANTARCTICA

The Ross ice drainage system comprises about 25 per cent of the surface area of the Antarctic Ice Sheet. Its fluctuations during the Late Quaternary have been determined in two ways: from analyses of three deep ice cores extracted at Byrd (West Antarctica) and at Vostok and Dome Circe (East Antarctica); and from the distribution, stratigraphy and chronology of glacial drifts in the Transantarctic Mountains. The ice core studies give time series records for the last 160 ka that correspond well with the marine isotope record and clearly show glacial, interglacial, stadial and interstadial intervals. They also suggest that during glaciation maxima, the polar plateau was characterised by an accumulation rate 50 per cent lower and temperature 7-9°C lower than present values. Glacial geological studies reveal a hiatus in the drift record between older (Miocene-Early Pleistocene) glacial sediments and drifts of the last two glaciations (Isotope Stages 6 and 2). There are two leading but contradictory interpretations of the older drift (Sirius Formation). One is based primarily on biological data and favours partial deglaciation of Antarctica in the Pliocene-Early Pleistocene followed by regrowth of the East Antarctic Ice Sheet to dimensions larger than now and then substantial uplift of the Transantarctic Mountains. The other is founded on glacial geological observations and implies a larger-than-present ice sheet over Antarctica during the Miocene and only 200 m of uplift subsequently. For the Late Quaternary, reconstructed ice surface profiles, based on detailed mapping and dating of drift sheets, show that large outlet glaciers from the East Antarctic polar plateau became about 1000 m thicker during glaciation maxima, while the plateau ice barely thickened at all. This is attributed to extensive northward migration of the ice grounding line in the Ross Embayment as global sea level fell. Dates obtained from the drift sheets confirm that glaciers in the Ross Embayment area reached maximal limits at 190-160 ka BP and at 23-14 ka BP. Recession from the last glaciation maximum was underway by 13 ka BP and was complete by ca. 6 ka BP. Alpine glaciers terminating in Dry Valleys fluctuate asynchronously with the Ross Embayment glaciers; they retreat during glacial maxima when they become starved of accumulation, and readvance during warmer intervals. Because of their dependence on grounding line position, glacier fluctuations in much of Antarctica are primarily led by sea level changes controlled by ice sheets in the northern hemisphere. © 1990.