MAPPING THE EXTENT AND TIMING OF EPHEMERAL ANTARCTIC WETLANDS USING HIGH-TEMPORAL RESOLUTION SATELLITE IMAGERY OF THE MCMURDO DRY VALLEYS

A cryptic hydrological system of subsurface groundwater channels called water tracks, water track-fed ponds, and seasonal perched wetlands drives many soil biogeochemical processes in Antarctic ice-sheet-free regions. However, the magnitude of their impact is not well understood because the duration of seasonal wetland conditions is unconstrained. Here high temporal resolution satellite imagery from Planet PlanetScope was terrain-corrected to identify the start of water track activity for summer 2018-2019. Wetted soil conditions emerged on equator-facing slopes in late November, while at the polar-facing site, they appeared later in mid-January. Water tracks on equator-facing slopes were present from November-February. These observations were then compared to on-the-ground soil temperatures measurements at depth from nearby MCM LTER met stations, where the start of water track activity coincides with subsurface (-10 cm) soil temperatures reaching the zero-degree isotherm. The relationship between slope azimuth and the start of water track activity suggests that ephemeral Antarctic wetland features are dependent on the amount of incoming shortwave radiation and not air temperature to increase soil temperatures above freezing. Water tracks form after subsurface melt wicks to the surface via capillary action, rather than by top-down snowmelt and infiltration. Once active, water tracks persist until February, often after surface temperatures fall below 0˚C which extends previous estimates of the water track hydroperiod (the time during which liquid water is present in soils) by upwards of a month. After correcting high temporal resolution satellite imagery for the effects of direct illumination on surface terrain, water tracks are visible for a broader range of time than was previously understood. A longer hydroperiod for subsurface meltwater features implies more time for chemical weathering in these soils and greater seasonal habitability for soil microorganisms.