Distinct Groundwater Regimes in West Antarctic Sedimentary Basins Inferred from Magnetotelluric Imaging.

Subglacial sedimentary basins in Antarctica are hypothesized to modulate ice flow and biogeochemical cycles via groundwater and geothermal feedbacks, yet their properties remain poorly constrained. As part of the International Thwaites Glacier Collaboration’s (ITGC) GHOST project, we acquired new magnetotelluric (MT) geophysical data on Thwaites Glacier (TG) and at the West Antarctic Ice Sheet (WAIS) Divide during the 2022/23 and 2023/24 austral summers.

These new data are integrated with an archive of existing MT profiles from the Whillans Ice Stream, Central West Antarctica, the South Pole, and the Ross Ice Shelf to provide a continent-scale perspective. Using a constrained 1-D transdimensional Bayesian inversion, we produce new depth-resistivity models for the uppermost crust beneath the ice at each location, and interpret these models in terms of geological, geothermal and hydrogeological conditions beneath each profile.

The new MT data reveal a shallow (< 5 km) 2-D crustal structure at TG aligned with the West Antarctic Rift System, overlying deeper 3-D architectures potentially linked to older tectonic frameworks, e.g., the Weddell Sea Rift System. Our inversion highlights that the sedimentary basin beneath TG exhibits relatively high resistivity (>10 Ωm), distinct from the low-resistivity (<10 Ωm) basins observed beneath the Whillans Ice Stream, South Pole and Ross Ice Shelf. Sensitivity analysis reveals that the TG basin is horizontally heterogeneous, with conductive signatures in thicker sections and resistive, potentially low porosity, fresh conditions at GHOST Ridge, a subglacial topographic high which has been identified as a potential future stabilizing point. Conversely, basins beneath Subglacial Lake Whillans and the South Pole exhibit vertical stratification, likely hosting fresh, cold upper layers above deep, saline, and potentially warm reservoirs.

We conclude that complex, spatially variable groundwater regimes are widespread in Antarctica. These contrasting hydrological environments imply continent-scale variability in subglacial thermodynamics and ice dynamics. Furthermore, they suggest spatially distinct biogeochemical potentials, influencing subglacial carbon sequestration and the rates of dissolved carbon discharge into the Southern Ocean.