GROUNDWATER – SURFACE WATER INTERACTIONS IN A POLAR DESERT, THE MCMURDO DRY VALLEYS, ANTARCTICA

The McMurdo Dry Valleys (MCM) @ ~78°S are the largest ice-free expanse in Antarctica. The hydrologic cycle in the MCM primarily consists of the seasonal melting of glaciers and the flow of this water through permanent stream channels into closed-basin lakes. Because of the polar desert conditions (mean annual T = -20°C and annual precipitation of <10 cm a-1), there is neither overland flow, nor obvious groundwater recharge in these environments. Yet work from the 1970's, and more recent research since the mid 1990's, indicates that surface/subsurface hydrological processes do occur in the MCM, and some processes have very important geochemical and biogeochemical consequences. This paper will briefly review the major groundwater-surface water processes that have been identified in the MCM region. They include: extensive and complex hyporheic zone exchange, evaporation from the stream and from the exposed surface of the hyporheic zone, subsurface ice melting and/or, precipitation storage and melt, deep groundwater flow and groundwater – lake exchange. Hyporheic zone dynamics in these polar desert streams are generally rapid compared to some temperate streams and zones of varying exchange rates are more readily identified using deuterium and oxygen isotopes. Hyporheic exchange rates control nutrient dynamics and chemical weathering in the stream channels and solute input to the lakes. Although there is measurable groundwater flow into some lakes, it varies in amount and geochemical significance that is primarily related to the landscape position of the lake. Our recent investigations indicate a number of groundwater seeps in the MCM and their sources of water are varied. The melting of subsurface ice is currently not a major contributor to water and chemicals to the lakes, but it could become more important as the climate warms. In general, the impact of future climate fluctuations on groundwater – surface water interactions in these polar deserts is not well understood.