The impact of the deformation description on the flow regime of Thwaites Glacier

Abstract:

Deformation and sliding are the main processes of ice flow in polar ice sheets. However, the relative contributions of these processes to overall flow is often poorly constrained in ice sheet models. Indeed, uncertainties surrounding basal sliding exceed those in ice deformation, and sliding parameters are frequently adjusted by inversion techniques to match the observed flow. Here, we investigate the influence of deformation on the flow regime of Thwaites Glacier by simulations comparing the Glen flow relation with the ESTAR flow relation that parameterizes ice anisotropy through taking into account the impact of different stress configurations on the strain rates. We find two key differences in the Thwaites deformation regimes. First, the ESTAR flow relation simulates larger local maxima in basal shear stresses than the Glen flow relation. This is because anisotropic effects in ESTAR lead to a lesser role for membrane stresses in distributing the basal shear stresses and countering the gravitational driving stresses. Anisotropy captured by ESTAR further enhances the vertical shear profile, implying less basal sliding than Glen. Second, in the slow-flowing interior of the catchment where the ESTAR flow relation predicts motion almost entirely by deformation, the Glen flow relation predicts basal sliding. Our results emphasize the important role of the quantitative description of deformation and anisotropy in the transition between deformation-dominated and sliding-dominated flow, and highlight the need for observational constraints in such regions.