SALSA EM: Mapping Subglacial Groundwater in Antarctica

Funding Program: NSF Antarctic Science
Start Date: 1 December 2017
End Date: 30 November 2022
Collaborating Institutions: Scripps Institution of Oceanography (lead), Columbia University

The Antarctic ice sheet is underlain by a dynamic water system that lubricates the flow of ice streams and outlet glaciers, provides a habitat for a diverse microbial ecosystem, and delivers freshwater and nutrients to the Southern Ocean. However, imaging this subglacial environment is difficult: Antarctica is a vast continent with ice up to four kilometers (2.5 miles) thick. To detect water at the ice-bed interface and in deeper groundwater reservoirs, this project will adapt a technique called electromagnetic sounding that is well-established on land and in the ocean for imaging fluids beneath the surface. Groundwater is estimated to be a significant part of the subglacial water budget in Antarctica, yet previous observational approaches have been unable to characterize its volume and distribution. This project will thus yield critical information about how ice-rock-water-ocean systems interact and inform our understanding of ice-sheet processes, global nutrient cycles, and freshwater flux to the ocean. The project will provide cross-disciplinary training for a graduate student and postdoctoral scientist, and develop an educational outreach program through the Birch Aquarium.

Standard geophysical surveying techniques used in glaciology to image subglacial water (radio-echo sounding and active-source seismology) are not directly sensitive to water content. In contrast, ground-based electromagnetic (EM) methods are sensitive to water content through its impact on bulk conductivity. Although EM methods are well-established for high-precision mapping of hydrology in other geological environments, their application on ice sheets is in its infancy. The proposed work will adapt both passive- and active-source EM techniques to glaciological questions to quantify the three-dimensional structure of subglacial water beneath an ice stream and in a grounding zone. The project will perform a suite of synthetic inversion studies to determine the range of applications of EM techniques in glaciology and execute a field experiment on the Whillans Ice Plain to investigate two hypotheses about the subglacial water system based on previous observational and modeling results: (1) Subglacial Lake Whillans is underlain by a deep, saline groundwater reservoir; and (2) there is an estuary-like zone of mixing between fresh subglacial water and seawater near, and possibly landward, of the grounding line.