Inversion of basal friction in Antarctica

ISSM paper presents features the first continental scale inversion of Antarctica at high resolution using a higher-order model.

Abstract:
Basal friction beneath ice sheets remains poorly characterized and yet is a fundamental control on ice mechanics. Here we use a complete map of surface
velocity of the Antarctic Ice Sheet to infer the basal friction over the entire
continent by combining these observations with a three-dimensional, thermomechanical, higher-order ice sheet numerical model from the Ice Sheet System Model open source software. We demonstrate that inverse methods can be readily applied at the continental scale with appropriate selections of cost function and of scheme of regularization, at a spatial resolution as high as 3 km along the coastline. We compare the convergence of two descent algorithms with the exact and incomplete adjoints to show that the incomplete adjoint is an excellent approximation. The results reveal that the driving stress is almost entirely balanced by the basal shear stress over 80% of the ice sheet. The basal friction coefficient, which relates basal friction to basal velocity, is, however, significantly heterogeneous: it is low on fast moving ice and high near topographic divides. Areas with low values extend far out into the interior, along glacier and ice stream tributaries, almost to the flanks of topographic divides, suggesting that basal sliding is widespread beneath the Antarctic Ice Sheet.

Reference:
Inversion of basal friction in Antarctica using exact and incomplete adjoints of a higher-order model, Morlighem, M., Seroussi, H., Larour, E. and Rignot, E., J. Geophys. Res., 2013, 118(3), 1746–1753

Download Document
Inferred basal friction coefficient of Antarctica that relates basal friction to basal velocity. The white lines indicate the location of ice topographic divides.