CHRONOLOGY OF PROGLACIAL AND LATERAL LAKES IN THE DRY VALLEYS

An understanding of lake sediments is key to interpreting the late Quaternary glacial history of the Dry Valleys. This is illustrated by the fact that almost all chronologic information for this area comes from algae or precipitates that formed in proglacial or lateral lakes. In addition, proglacial lakes can transport glacial sediments tens of kilometers beyond the grounding line by a process known as the lake-ice conveyor. Conveyor sediments make up a unique landform assemblage, the identification of which is necessary to interpretations of former glacier extent and chronology.

During the last glacial maximum (LGM), lakes several hundred meters deep filled the Dry Valleys. AMS radiocarbon and TIMS uranium-thorium dates of algae and carbonate precipitates indicate that all lakes were significantly higher than at present by 20,000 14C yr B.P. Many of these lakes afford important information on the extent, thickness, and dynamics of the Ross Sea ice sheet, as well as of local glaciers. For example, the presence of lacustrine sediments to 350 m elevation in Taylor Valley requires thick grounded Ross Sea ice in the valley mouth in order to dam the lake. In nearby Wright Valley, Glacial Lake Wright reached 566 m elevation, indicating that the Wilson Piedmont Glacier must have been at least 100 m thicker at the LGM than it is today. Otherwise, the lake would have drained. Conversely, the presence of lacustrine sediments of infinite age thrust up within Victoria Lower Glacier suggests that the glacier is now at its maximum extent in at least the last 50,000 years. Current work is focusing on developing a chronology of lake-level fluctuations and on improving understanding of any lake-bottom radiocarbon reservoir effects.