TRACKING ANTARCTICA'S BRINES: SOIL AS A MEDIATOR OF GROUNDWATER AND ECOSYSTEM PROCESSES IN THE MCMURDO DRY VALLEYS

Water tracks are zones of high soil moisture that route water downslope over the ice table in polar environments. We present physical, hydrological, and geochemical evidence collected in Taylor Valley, McMurdo Dry Valleys, Antarctica, which suggests that water tracks constitute the primary groundwater flow path in a cryptic hydrological system operating in Antarctica’s ice-free areas. Because the active (thawed) layer of the soil is the only part of this landscape that is seasonally unfrozen, Antarctic crysols are a major mediator of Dry Valleys hydrology. Here, we present new data from the 2012-2013 field season that tests the hypothesis that soil controls on groundwater flowpaths and water sources provides structure to Antarctic soil ecosystems. Geological, geochemical, and hydrological analyses show that the water tracks are generated by a combination of infiltration from melting snowpacks and melting of pore ice, and soil salt deliquescence. Water tracks are enriched in solutes derived from chemical weathering of soil sediments as well as from dissolution of soil salts. Previous estimates indicated that groundwater flow in Antarctica is ~100 times smaller than surface runoff. He we present new estimates of the groundwater flux through seasonally thawed Dry Valleys soils based on in-situ and remote-sensing measurements. We show that the solute delivery to Antarctic lakes by water tracks equals or may exceed the mass of solutes delivered from stream flow, making water tracks major geochemical pathways. Additionally, solute transport is two orders of magnitude faster in water tracks than in adjacent dry or damp soil, making water tracks “salt superhighways” in the Antarctic cold desert. Accordingly, water tracks are a new geological pathway that distributes water, energy, and nutrients in Antarctic Dry Valleys cold desert, soil ecosystems, providing hydrological and geochemical connectivity at the hillslope scale.