The Antarctic Ice Sheet sliding law inferred from seismic observations

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 select among them. Here, we use satellite observations of ice flow, inverse methods, and a theory of acoustic propagation in granular material to relate the effective pressure, which is a key control of basal sliding, to seismic observations recovered from Antarctica. Together with independent estimates of grain diameter and porosity from sediment cores, this enables a comparison of basal sliding laws within a Bayesian framework. The presented direct link between seismic observations and sliding law parameters can be readily applied to any acoustic impedance data collected in a glacial environment. For rapidly sliding tributaries of Pine Island Glacier, these calculations provide support for a Coulomb sliding law and widespread low effective pressures.