Comparisons of Ice Sheet Model Inversions with Basal Reflectivity from Airborne Radar for Thwaites Glacier, West Antarctica

Abstract:

Thwaites Glacier is a large, fast moving and fast changing glacier in West Antarctica. Studies show that the fast flow triggers basal processes such as shear heating under regions where the glacier moves fast (generally > 50 ma^–1). Large volumes of liquid water persist in these regions that can accumulate in ponds and flow in subglacial channels. Presence of water at the bed results in the glacier sliding on its bed and acceleration. Basal slipperiness is an important boundary condition for ice sheet models and is not known precisely. Here, we use three years of airborne ice penetrating radar data from IceBridge campaign to estimate basal reflectivity parameter. Areas of high basal reflectivity may indicate presence of liquid water, either fresh, or from the ocean if close to the grounding line. Our reflectivity estimates show high reflectivity along the grounding zone as well under the subglacial lakes. As a part of ITGC PROPHET modeling experiments, three ice sheet models – ISSM, Úa and STREAMICE invert for basal slipperiness under Thwaites Glacier and the inversions are compared with airborne radar reflectivity. All three ice sheet models use the same boundary conditions, Weertman’s sliding law, and invert for the basal friction parameter. We provide detailed discussions of the comparisons of radar derived reflectivity and modeled basal conditions, and likely intrusion of ocean water at the grounding line of Thwaites Glacier.