WATER TRACK HYDROPATTERN IN THE MCMURDO DRY VALLEYS, ANTARCTICA: CONTRASTING VIEWS FROM SPACE AND FROM THE SUBSURFACE (Invited Presentation)

Recent observations of accelerating erosion and ground ice thaw in Antarctica’s coastal Dry Valleys (MDV) suggest that shrinking permafrost extents, thickening active layers, and widespread thermokarst subsidence resulting from enhanced heat transport through recently-wetted cold desert soils may be early indicators of imminent, continental-scale change in the topography, mineralogy, and the thermal state of the Antarctic terrestrial cryosphere. Water tracks are the basic unit of the subsurface hydrological system that feeds polar and permafrost wetlands. Water tracks are narrow bands of high soil moisture that route water downslope through soils, in the absence of overland flow. In water tracks, moisture moves as shallow groundwater, flowing through the active layer (the seasonally-thawed portion of soil column) along linear depressions in the ice table (the top of the permafrost that remains ice-cemented during summer). Because they are soil landforms, water tracks are notoriously difficult to measure because they cannot be easily gaged like a stream.

Efforts to determine the duration, extent, and saturation of water tracks in the MDV (the hydropattern) require measurements at a range of scales: from satellite observations of regional water track wetting and soil darkening, to the plot-scale, where subsurface temperature and soil moisture conditions can be met. Here, we show that water track soil moisture conditions, and by extension, the magnitude of soil biogeochemical cycling that can occur, show mis-matches, depending on the scale and mode of observation. Water track thawing and soil moisture development typically begins early in the austral summer during November, when soil temperatures are still at or below 0˚. In contrast, soil darkening from wetness exceeding a few weight percent water does not typically begin until December or later, as observed through satellite observations. This mismatch suggests that soil biogeochemical processing in water track moisture anomalies may be occurring “cryptically” in the shallow subsurface, long before seasonal thawing is apparent to remote surface observations.