EFFECTS OF CHANGING WATER LEVELS ON LAKE FRYXELL AND LAKE HOARE, TAYLOR VALLEY, AS EVIDENT BY CHLOROFLUOROCARBON, HELIUM, AND TRITIUM PROFILES

In the 1990s, the Taylor Valley lakes had low water input from streams and glaciers; however, during the 2001-02 austral summer, there was a major melt event that increased lake levels dramatically. During the 2002-03 Antarctica field season, we collected water samples for chlorofluorocarbons (CFCs), ⁴He, and ³H from Lake Fryxell and Lake Hoare in the Taylor Valley to evaluate the effects of this extremely high melt water year. The comparison of these data from 2002-03 to previous data from the 1980s and 1990s allows us to better understand the effects that high flow years have on lake dynamics. The CFC profiles of Lakes Hoare and Fryxell, from the 1994-95 and 2002-03 seasons, are similar. The data indicate that a pulse of fresh water has flowed onto the surfaces of the lakes during this time period and not mixed with the underlying water. Lake Hoare and Lake Fryxell have very different dissolved ⁴He profiles, in concentrations and profiles. The ⁴He profiles from the 1999-2000 and 2002-03 field seasons show that fresh water flowed into both lakes, causing them to rise and become more dilute. In the case of Lake Hoare, ⁴He data from the lower depths suggest that younger water has mixed with the bottom waters. The pulse of fresh water from the high melt water year of 2001-02 can explain the variations in the CFC and ⁴He profiles between sampling seasons in Lake Fryxell and Lake Hoare. The profiles of tritium data from previous years (1987-88, 1988-89, 1993-94, and 1999-2000) demonstrate that tritium values increase during the wetter years and decrease in drier years. The variations in the tritium profiles between the lakes are caused by different water “sources” for the lakes. The main source of ³H-rich water for Lake Fryxell are the lengthy streams generated by snow melt while the direct input from Canada Glacier and short streams are the ³H-poor water sources for Lake Hoare.