MCMURDO DRY VALLEYS, ANTARCTICA AS A LAKE PROXY FOR MARS: CLOSED-BASIN VERSUS FLOW-THROUGH SYSTEMS

The McMurdo Dry Valleys, Antarctica (~78°S) are thought to be one of the best analogies for Martian environments on Earth. Studies have established past hydrologic activities across the southern highlands of Mars, which include the recognition of paleolakes. Both flow-through and closed-basin lakes have been delineated on Mars, but recent work has indicated that closed-basin ones are more widespread than previously thought. The MCM Dry Valleys contain several permanently ice-covered lakes. While most of these lakes are closed-basin systems, Lake Miers is the only flow-through lake present in the area, thereby retaining and geochemically processing chemicals differently. Lake Miers is the freshest of the MCM Dry Valley lakes and shows chemical differences from the others, including Lake Hoare, the freshest closed-basin lake in nearby Taylor Valley. While surface waters for these two lakes contain similar concentrations of major ions (0.025-0.35 mM and 0.019-0.49 mM of Ca and Cl, respectively, for both lakes), the waters at depth are dissimilar, with Lake Miers showing minimal increases in bottom water to 0.85-1.06 mM of Ca and 0.17-0.24 mM of Cl, and Lake Hoare showing greater increases in bottom water to 1.85-2.07 mM of Ca and 6.09-6.74 mM of Cl. Other, older closed-basin lakes in the MCM Dry Valleys have bottom water Cl values as high as 5.6 M. Although the concentrations of Ca in surface waters of the lakes are similar, for Miers Ca comprises 60-85% of all total cations. In Hoare Ca makes up closer to 15-24% and the major cation is Na. For all major ions measured except Ca, Lake Hoare’s surface waters are at least four times more concentrated than the surface of Miers. The chemistry of lakes in the MCM Dry Valleys is affected first by hydrologic system, whether the lake is closed-basin or flow-through, and second by all other geochemical factors. We would expect similar differences in the Martian paleolakes.