LATE QUATERNARY ICE FLUCTUATIONS IN SOUTHERN VICTORIA LAND

Knowledge of the extent, volume, and chronology of Antarctic ice-sheet fluctuations during the late Quaternary is key to understanding the Southern Hemisphere contribution to sea-level, ocean-circulation, and paleoclimatic changes. Over the past several years, detailed surficial geologic mapping, coupled with radiocarbon and uranium-thorium chronologic data, have led to an improved understanding of ice-sheet history in southern Victoria Land. AMS radiocarbon dating has allowed chronologies to be constructed for features, such as raised beaches, that could not be dated previously. Improved techniques in uranium-thorium dating have resulted in better age control for earlier glaciations. As a result, there are now more than 400 dates from southern Victoria Land that bear on the history of both the East Antarctic Ice Sheet and grounded ice in the Ross Sea Embayment during late Quaternary time.

Data from the Dry Valleys confirm the out-of-phase relationship between East Antarctic outlet glaciers and Ross Sea ice in this region. For example, during interglacial periods, Taylor Glacier thickens and advances. During glaciations, however, it retreats, while the Ross Sea Embayment fills with a grounded ice sheet, derived largely from West Antarctica. This Ross Sea ice sheet flows landward into the mouths of the valleys opening onto McMurdo Sound. Chronology comes from AMS radiocarbon dates of algae that lived in ice-dammed and lateral lakes. These data indicate that grounded Ross Sea ice was present along the coast between 23,800 and 8340 14C yr B.P. Ice reached 350 m elevation at the mouth of Taylor Valley, where a moraine dating to 12,700-14,700 14C yr B.P. marks the upper limit. Ice was still near this position as late as 10,800 14C yr B.P. The timing of retreat, ~6600 14C yr B.P., comes from relative sea-level curves from the adjacent coast. Larger-scale reconstruction indicates that most grounding-line recession in the Ross Sea Embayment occurred during the Holocene.