Importance of basal processes in simulations of a surging Svalbard outlet glacier

Abstract

Abstract. The outlet glacier of Basin 3 (B3) of Austfonna icecap, Svalbard, is one of the fastest outlet glaciers in Svalbard, and shows dramatic changes since 1995. In addition to previously observed seasonal summer speed up associated with the melt season, the winter speed of B3 has accelerated approximately five fold since 1995. We use the Elmer/Ice full Stokes model for ice dynamics to infer spatial distributions of basal drag for the winter seasons of 1995, 2008 and 2011. This "inverse" method is based on minimising discrepancy between modelled and observed surface velocities, using satellite remotely sensed velocity fields. We generate steady state temperature distributions for the three time periods. Frictional heating caused by basal sliding contributes significantly to basal temperatures of the B3 outlet glacier, which exhibits a uniform steady state basal temperature at pressure melting point in all three cases. We present a sensitivity experiment consisting of transient simulations under present day forcing to demonstrate that using a temporally fixed basal drag field obtained through inversion can lead to thickness change errors of the order of 2 m per year. Hence it is essential to incorporate the evolution of basal processes in future projections of the basin. Informed by a combination of our inverse method results and previous studies, we hypothesize a system of processes and feedbacks involving till deformation and basal hydrology to explain both the seasonal accelerations and the ongoing inter-annual speed up, and speculate on the wider relevance of deformable till mechanics to non-surging glaciers.

Glacial cycles simulation of the Antarctic Ice Sheet with PISM – Part 1: Boundary conditions and climatic forcing

“…Value q = 0 represents plastic (Coulomb) deformation 370 of the till where ice is flowing over a rigid bed with filled cavities (Schoof, 2005(Schoof, , 2006. Many studies use q = 1/3 (Schoof, 2007a;Pattyn et al, 2013;Gillet-Chaulet et al, 2016) or a linear sliding relationship between basal velocity and basal shear stress for q = 1, as most commonly adopted for (Larour et al, 2012;Gladstone et al, 2013;Yu et al, 2017). Note, that u b results from solving the non-local SSA stress balance (Bueler and Brown, 2009, Eq.…”

Simulating the Early Holocene demise of the Laurentide Ice Sheet with BISICLES (public trunk revision 3298)

“…This is a simplification of the subglacial hydrology, which comprises several processes that can alter the dynamics of ice flow on different time scales (Clarke, 2005;Gladstone et al, 2014). The motion of the base of an ice sheet can be due to (typically plastic) deformation of the underlying sediment or the base of the ice sheet actually sliding on top of the underlying substrate (Gladstone et al, 2014). The sliding is facilitated by the presence and distribution of liquid water at the base, and the yield stress of the deformation of the till is strongly dependent on effective pressure (Iverson, 2010).…”