EVIDENCE FOR MILLENNIAL-SCALE FLUCTUATIONS OF CLOSED-BASIN LAKES IN THE DRY VALLEYS

The presence of relict shorelines and deltas as much as 460 m above present-day water level indicates that closed-basin lakes in the Dry Valleys have been significantly larger than they are now. Radiocarbon and uranium-thorium dating of preserved algae and lacustrine carbonates show that these large lakes were present during the last glacial maximum and into the Holocene. Our work concentrates primarily on the three main valleys (Taylor, Wright, and Victoria), although we believe that most, if not all, valleys supported large lakes at the last glacial maximum.

We have dated more than 130 deltas and shorelines in the Dry Valleys. The elevations of these features, coupled with the dates, allow us to construct lake-level curves for basins in the three valleys. All curves show high-frequency, high-magnitude surface water-level changes. Although higher-than-present lakes were in existence as early as ~28,000 cal yr B.P., the oldest well-defined peak is centered at 22,000 cal yr B.P. Fluctuations of as much as 250 m occurred approximately every 1000-1500 years, rarely every 500-800 years. The youngest, well-defined peak is at ~9000 cal yr B.P. Other lake-level highstands occurred during the Holocene, particularly at ~6000 and ~3000 cal yr B.P., but our data are not complete for those time periods.

The level of closed-basin lakes in the Dry Valleys is controlled by the balance between incoming glacial meltwater and sublimation. The presence of such large lakes indicates that a significantly different environment and hydrologic regime existed during the last glacial maximum. We attribute the large water-level variations to changes in meltwater production and input. Meltwater production today is sensitive to changes in both temperature and snow cover. Snow cover, in particular, has the detrimental effect of both inhibiting glacial melting and significantly increasing the albedo of the Dry Valleys. With that it mind, we suggest that the high lake levels occurred during periods of reduced snowfall and locally warmer temperatures. Whether these warmer temperatures were the result of a very low local albedo brought about by aridity, or a more regional climate signal remains unknown.