SHALLOW GROUNDWATER AND BRINE PROCESSES IN ANTARCTICA: UNCOVERING THE ROLE OF WATER TRACKS IN THE MCMURDO DRY VALLEYS

Berry Lyons helped establish the hydrological and geochemical paradigm we use to understand the McMurdo Dry Valleys (MDV) today by connecting upstream processes in glacier watersheds to stream geochemistry, and ultimately to the chemical processes that shape the climate records preserved in MDV lakes and the functioning of the modern lake ecosystems. This “freshwater” system in the MDV has long served as the dominant paradigm for understanding hydrological processes in the MDV, but ultimately did not account for soil water processes in Antarctic ecosystems outside of the wetted perimeter of streams and lakes. Recent collaborations with Dr. Lyons have shed new light on the origin and evolution of the saline to hypersaline shallow groundwater system at work in the MDV. We report on measurements of soil water geochemistry and soil hydrological properties from the MDV, and relate them to changes in the spatial patterns of shallow groundwater flow (water tracks), landscape subsidence (thermokarst), and microbial and invertebrate ecosystem response. We show that shallow groundwater in the MDV is primarily derived from snowfall and seasonal ground ice melt, but is evaporatively concentrated during the summer flow period to produce saline to hypersaline active layer solutions. Evaporative concentration of water track fluids, coupled with soil salt dissolution, and/or cation exchange reactions, results in enrichment of water track fluids in chloride and sulfate salts (depending on local soil chemistry) such that initially fresh snowmelt becomes saline to hypersaline over several km of groundwater flow. In this manner, water track geochemical divides mirror pond geochemical divides in Antarctica, suggesting a groundwater origin for many small Antarctic ponds and lakes. Water track brines shape soil ecosystems in the MDV by controlling salinity-dependent habitat suitability for invertebrates and microbial organisms. Because water tracks are primarily snow-fed, and are moderated by shallow active layer processes, they represent a component of the Antarctic hydrological system that is likely to respond rapidly to regional changes in temperature and precipitation, altering Antarctic terrestrial ecosystems, carbon budgets, and ground ice distribution.