Upper-Crustal Structures Beneath Thwaites Glacier, West Antarctica and their Influence on Ice Dynamics

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, 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 estimates of the rate of ice-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. We use a combination of active-source seismic, ice-penetrating radar and aerogravity data collected on TG to investigate whether upper-crustal structures can exert a fundamental control on TG’s ice dynamics. We focus especially on the distribution of sedimentary basins and their association with variability in the ice basal rheology and/or variations in basal-shear stress inferred from modeling.

Seismic-reflection/refraction and radar profiling data collected along the main trunk of TG about 250 km inland of the current grounding line indicate the presence of ~10-km wide, >100-m deep sedimentary basin with a relatively smooth ice-bed interface. A co-located Bouguer gravity-anomaly profile, derived from NASA’s Operation IceBridge aerogravity data, 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-flow modeling. Therefore, we hypothesize that, for at least this location, the sedimentary basin provides a soft, smooth bed for ice flow; hence, upper-crustal structures are closely linked to the basal properties of TG.