CL-36 IN THE WATERS OF THE MCMURDO DRY VALLEY LAKES, SOUTHERN VICTORIA LAND, ANTARCTICA - REVISITED

We have analyzed water samples from lakes Bonney, Fryxell, and Hoare i n the McMurdo Dry Valleys (MDV) area of southern Victoria Land, Antarc tica. These data, coupled with those of earlier work, provide a new vi ew of the sources of chloride ion to these lake systems. Although thes e lakes lie within the same geologic domain and climatic regime, their chemistries are very different in that the hypolimnions have varying salinities and major ion ratios. The bottom waters of both lobes of La ke Bonney have low Cl-36:Cl ratios (<6 x 10(-15)) derived from a proba ble mixture of seawater (0 x 10(-15)) and a nearby saline seep (9-10 x 10(-15)). On the other hand, the Cl-36:Cl ratio of both the bottom wa ter and the surface water of Lake Hoare, the least saline of the lakes , is similar to ratios found in chloride salts in the local soil and m eteoric sources by the earlier work (210 vs. 440 X 10(-15)) of Carlson et al. (1990). The water from Lake Fryxell has an intermediate ratio, perhaps indicating a mixture of both meteoric input and ''older'' chl oride. Our recent surface-water measurements from the three lakes demo nstrate a very significant decrease in the Cl-36:Cl ratio from the mel twater that entered the lakes in 1984-1985. These data provide evidenc e of the dynamic geochemical/hydrological behavior of these lakes, and coupled with the earlier data, help to better define the importance o f differing sources of solutes to the lakes. Copyright (C) 1998 Elsevi er Science Ltd.