Inferring the ice sheet sliding law from seismic observations: A Pine Island Glacier case study

The response of the Antarctic ice sheet to climate change and its contribution to sea level under different emission scenarios are subject to large uncertainties. A key uncertainty is the slipperiness at the ice sheet base and how it is parameterized in glaciological projections. Alternative formulations of the sliding law exist, but very limited access to the ice base makes it difficult to validate them. Here, the Viscous Grain-Shearing (VGS) theory of acoustic propagation in granular material, together with independent estimates of grain diameter and porosity from sediment cores, is used to relate the effective pressure, which is a key control of basal sliding, to seismic observations recovered from Pine Island Glacier, Antarctica. With basal drag and sliding speed derived through satellite observations of ice flow and inverse methods, the new Bayesian sliding law inference-VGS (BASLI–VGS) approach enables a comparison of basal sliding laws within a Bayesian model selection framework. The presented direct link between seismic observations and sliding law parameters can be readily applied to any acoustic impedance data collected in glacial environments underlain by granular material. For rapidly sliding tributaries of Pine Island Glacier, these calculations provide support for a Coulomb-type sliding law and widespread low effective pressures.