THE GEOCHEMISTRY OF THE TAYLOR VALLEY LAKES, ANTARCTICA

The McMurdo Dry Valleys (MDV) are the largest ice-free expanse in Antarctica. Even though the MDV are a polar desert with less than 10 cm of precipitation per year, they contain a number of perennially ice-covered lakes. Taylor Valley contains three large, closed-basin lakes that have been the primary focus of the McMurdo Dry Valleys Long-Term Ecological Research investigations for ~20 years. The salinity and major ion ratios of these three lakes are very different; the hypolimnia of Lake Bonney, Lake Fryxell and Lake Hoare are hypersaline, brackish and fresh, respectively. These differences reflect, in part, the evolutionary history and age of the lakes as well as their landscape position. The lakes respond rather rapidly to changes in austral summer temperature. Warmer summers produce more glacier melt (the primary source of water), which in turn impacts the surface water chemistry of the lakes. In this paper, we will review the differences in chemistry of these three lakes and the processes and reactions occurring in the lakes. Using the freshest water lake as the primary example, we will demonstrate how hydrological variations driven by summer temperature changes effect the chemistry changes in the lake. We will compare the geochemistry of Lakes Hoare and Fryxell and discuss the source of their differences. Our most recent work suggests that aeolian debris deposited on glacier surfaces may play a much more important role in lake geochemistry than previously thought. Finally, we will speculate on the future of these lakes in a warming climate.