PRELIMINARY INTERPRETATIONS OF THE GROUNDWATER FLOW SYSTEM OF WRIGHT VALLEY, ANTARCTICA USING STABLE ISOTOPES AND NOBLE GAS

The McMurdo Dry Valleys (MDV), Antarctica, is the largest relatively ice-free region on the Antarctic continent. Lake Vanda, Don Juan Pond, and Onyx River are located in Wright Valley, MDV. Lake Vanda is the deepest lake (~72 m) among the MDV lakes; it is situated in the center of Wright Valley. It has a relatively fresh water layer above 50 m with a calcium-chloride brine at its bottom. Don Juan Pond, which is west of Lake Vanda, is a shallow calcium-chloride pond that does not freeze during the Antarctic winter. The Onyx River is the longest flowing river on Antarctica; it flows westward from the coastal Lower Wright Glacier and discharges into the centrally located Lake Vanda. Several investigations have tried to address the source of the atypical calcium-rich brines measured in Lake Vanda's deep bottom waters and Don Juan Pond shallow water. In an intense international research effort between 1972 and 1974, several wells were drilled and sampled in Wright Valley in an effort to answer this question. Suggested by the published literature and this study, there is an active groundwater system in the Wright Valley. The combination of new and published stable isotopes, major ions, and noble gas data indicate that Don Juan Pond and bottom waters of Lake Vanda may have the same source of the water—groundwater. The dissolved gas of the bottom waters of Lake Vanda display solubility concentrations rather than the Ar-enriched dissolved gas seen in the Taylor Valley lakes. The isotopic data indicate that the bottom calcium-chloride-brine of Lake Vanda has undergone very little evaporation while the brine in Don Juan Pond has experienced intense evaporation. The groundwater samples plot on the evaporation line between Lake Vanda and Don Juan Pond. The calcium-chloride chemistry of the groundwater that discharges into Don Juan Pond and Lake Vanda most likely results from chemical weathering within the glacial sediments of Wright Valley and not evaporation. Our work supports previous physical and chemical observations that the upper portion of Lake Vanda is active while the hypersaline bottom layer is not. The helium and calcium chloride values are concentrated at the bottom, with a very narrow transition layer between it and the above fresh water. If the freshwater layer did not actively circulate, then the helium and brine would have diffused throughout the water column.