Abstract

Uncertainty related to the mechanics of the fast motion of the Greenland Ice Sheet plagues predictions of sea level rise. A large part of this uncertainty is tied to which constitutive relationship and associated parameters should be used to describe basal sliding. This talk looks at new results from high-resolution modelling over 4 by 8 km domains, incorporating temperate ice rheology and statistically realistic bed topography, which demonstrate that basal sliding exhibits large variability, from 90% over sub-kilometre distances. This indicates that basal motion is better considered as the sum of basal sliding and ice deformation within a basal temperate ice boundary layer that, in agreement with field studies, varies in thickness from 100 m in response to changes in basal topography. While this work focusses on the Greenland Ice Sheet it is likely that these findings also apply to Isbræ-type outlet glaciers in Antarctica which have similar roughness characteristics.