CAUSES AND CHARACTERISTICS OF AIRBORNE ELECTRICAL RESISTIVITY VARIABILITY IN SHALLOW (less than 4 M) SOILS IN TAYLOR VALLEY, EAST ANTARCTICA

We used two airborne electromagnetic (AEM) surveys collected in December of 2011 and November of 2018 and three soil geochemical transects to analyze the spatial heterogeneity of shallow (<4 m) soil properties in lower Taylor Valley, East Antarctica. A combination of subsurface AEM resistivity, soil geochemical, and meteorological data were used to characterize soil moisture distribution and determine the climate variables and soil properties associated with near-surface soil thaw. Soil resistivities from 2011 and 2018 range from 33.2 Ωm to 3535 Ωm with low elevations of <50 meters above sea level (masl) typically displaying the lowest resistivities and higher elevations displaying greater resistivities. Low resistivity soils were detected at similar locations in 2011 and 2018, but 2018 resistivities were generally greater in areas where the two AEM surveys overlapped. Soil moisture was empirically estimated from electrical resistivity values using Archie’s Law and range from 0.1% to 68.2%. Additionally, soil transect data exhibit greater prevalence of fine-grained sediments (<63 µm) below 100 masl where low resistivity materials occur most frequently. Low resistivities (<200 Ωm) are interpreted to be unfrozen soils with varying soil moisture contents while higher resistivities (>200 Ωm) are explained by completely to partially frozen soils with little to no pore water. An increase in silt- and clay-sized fractions at low elevations lead to greater capillary attraction that promotes increased soil moisture. Soil resistivity variability between 2011 and 2018 shows soils at different stages of soil freeze-thaw cycles, which are explained by differences in soil temperatures at the time of each AEM survey. Soil geochemical properties are highly heterogeneous in the shallow subsurface of lower TV and differ at high and low elevations primarily due to differences in soil moisture, which is controlled by local climate conditions and accumulation of solutes. This study furthers the understanding of the hydrogeologic structure of the shallow subsurface in Taylor Valley and identifies locations of soils that are potentially prone to greater rates of thaw and ecosystem homogenization of soil properties due to projected increases in hydrological connectivity across the region over the coming decades.