Modeling of the Upper Crustal Structure Beneath Thwaites Glacier, West Antarctica with Ground-Based and Airborne Geophysical Data

Abstract:

Ice-mass loss in the Amundsen Sea sector of West Antarctica has nearly doubled in the past four decades and continues to increase at an accelerating pace. Mass loss from Thwaites Glacier (TG) now rivals that from Pine Island Glacier (PIG) and modeling and observational studies indicate that TG may have begun an irreversible retreat into a deep marine basin. This retreat may initiate the disintegration of the West Antarctic Ice Sheet sometime in the next several hundred years. However, models cannot yet provide accurate prognostic estimates of ice-sheet mass loss and the resulting sea-level rise. One large unknown in modeling studies is the role of geologic controls on ice dynamics in the TG basin. In the past decade, a series of ground-based and airborne geophysical campaigns were conducted to collect data needed to address this issue. Here we use a combination of active-source seismic, ice-penetrating radar and aerogravity data collected on TG to investigate whether subglacial geology can extert a fundamental control on TG’s ice dynamics. We focus especially on the distribution of sediment pockets or basins and their association with variability in the ice basal rheology and/or variations in basal-shear stress inferred from modeling studies.

Preliminary analysis of seismic-reflection profiling data collected along the main trunk of TG ~250 km inland of the current grounding line indicates the presence of a ~10-km wide sedimentary basin. The Bouguer gravity anomaly, derived from aerogravity data collected by NASA’s Operation IceBridge, shows a local gravity-anomaly low that approximately matches the location of this seismically-inferred sedimentary basin. Moreover, this sedimentary basin roughly corresponds to a region of low basal-shear stress inferred from ice-sheet modeling. Thus, in at least this location, available geophysical observations suggest geologic controls on the basal properties of TG.