ANTARCTIC AERIAL ELECTROMAGNETIC RESISTIVITY (AEM): UNDERSTANDING LOW-RESISTIVITY ANOMALIES IN MCMURDO DRY VALLEYS AND BRINE INFILTRATION IN THE MCMURDO ICE SHELF

The McMurdo Dry Valleys (MDV) and McMurdo Ice Shelf (MIS) are two major regions of study in coastal Antarctica. Earlier ground penetrating radar and aerial electromagnetic (AEM) resistivity surveys identified widespread brine within valley sediments and ice shelf pore space.

Reciprocal to conductivity, resistivity gauges a material's resistance to energy flow. AEM utilizes EM waves emitted from an airborne instrument below a helicopter to penetrate surfaces and substrates and measure EM conductivity. AEM data is inverted into resistivity values and plotted in 2D and 3D models of substrate resistivities. Ongoing mathematical analysis estimates brine volume and depth, with results integrated into ArcGIS for visual models accentuating anomalies and offering a contextual overview.

The MIS is well explored due to its accessibility from the McMurdo Station on Ross Island. Building upon related research, the initial AEM surveys of the MIS were completed in 2011 and 2018 and aimed to understand the dynamics between the ice shelf and sea water infiltration to determine the ice shelf's response to a warming climate. Sea water likely infiltrates MIS through the porous firn layer on the shelf face through fissures. The MIS area of interest is 2,915 km², and the average inland extent of data collected is 22.5 km. For our threshold of a resistivity < 100Ωm, brine occurred at an average depth of 48.3807 m for the first resistivity value (ρ₁) recorded at each coordinate point. The mean resistivity, where ρ₁<100Ωm, is 31.5439 Ωm, enabling an estimated porosity (brine resistivity assumed at 0.36 (seawater at -1.9C)) at m= 1.5, 2.0, and 2.5, of 5.07%, 10.68%, and 16.71%, respectively.

The MDV is the largest ice-free region in Antarctica and an interesting candidate for its system of lakes and aquifers. AEM data from 2011 found a low resistivity anomaly in Wright Valley (WV), which was found in exposed bedrock in an elevated, low porosity region. Hence, we suspect that sulfides originating from hyperthermal altercation are likely causing the observed low resistivity. Hyperspectral data from WV may reveal mineral properties contributing to the anomaly. Cryoconcentration of brines in MDV would enable it to remain in a liquid state, while there lies the potential for an aquifer connectivity to the ocean.