Inferring basal stress under Greenland’s big three outlet glaciers

Wednesday, 17 December 2014
Daniel Shapero, University of Washington Seattle Campus, Seattle, WA, United States, Ian R Joughin, Univ Washington, Seattle, WA, United States, Kristin Poinar, University of Washington, Seattle, WA, United States and Mathieu Morlighem, University of California Irvine, Irvine, CA, United States
Friction at glacier beds plays a large role in determining the response of Greenland’s ice streams to changing external conditions, and yet this quantity remains unobservable by remote sensing. However, one can invert available observations of ice thickness and velocity to infer the spatial distribution of glacial bed stress that is most consistent with existing measurements. We have performed inversions for Greenland’s three largest outlet glaciers: Jakobshavn, Helheim and Kangerdlugssuaq. Many previous studies have employed depth-averaged glacier models; we have instead used a full Stokes model, as implemented in the software package Elmer/ICE. For all three glaciers, we found that their beds provided almost no frictional resistance to the driving stress. This finding is in keeping with observations that ice thinning extends very far upstream of the terminus. Finally, we address how much predictive validity these inversions possess given the presently available observational data.