MILLENNIAL-SCALE VARIATIONS OF LAKE VANDA, ANTARCTICA

Geomorphologic and sedimentologic data reveal rapid, high-magnitude, and cyclical changes in the level of Lake Vanda, a closed-basin lake in the Dry Valleys, Antarctica (77^o32'S, 161^o33'E, ~85 m elevation). Radiocarbon-dated relict deltas and shorelines, perched high on the valley walls, indicate former water levels as much as 480 m above present. Surface area of the lake expanded by a factor of 40. Moreover, water level was not static; rather, it fluctuated on a millennial timescale throughout both the last glacial maximum and the Holocene.

This past field season, we obtained ten sediment cores from the present Lake Vanda. The stratigraphy of these cores confirms the high-magnitude fluctuations seen in the deltaic record and elucidates the existence and timing of lowstands. Repeated sequences of algal-rich sand, carbonate, and gypsum indicate intervals of high lake level separated by periods of dessication. The most recent drying event occurred 1000-1300 calendar years B.P., based on U-Th dating of carbonate. This confirms an earlier prediction based on the salt diffusion gradient. Taken together, the geomorphologic and sediment core data provide a detailed record of millennial-scale water-level change at Lake Vanda over the last 25,000 years.

Fluctuations of Dry Valleys closed-basin lakes are thought to result from variations in meltwater production. Meltwater formation is greatest on clear, sunny days with high absorbed solar radiation. Snow cover hinders production by increasing local albedo (decreasing temperature) and preventing melt of the glacier surface. We suggest that the large-scale increases in water level seen at Lake Vanda and other nearby lakes result from enhanced absorption of solar radiation, related to millennial-scale changes in cloud/snow cover, temperature, and possibly solar variability.