Response of the large-scale subglacial drainage system of Northeast Greenland to surface elevation changes

Abstract

Abstract. The influence of subglacial water on the dynamics of ice flow has been the object of increasing interest in the past decade. In this study we focus on large-scale, longterm changes in surface elevation over Northeast Greenland and the corresponding changes in subglacial water routeways. Our results show that over timescales ranging from decades to millennia the area may experience redistribution of and fluctuation in subglacial water outflux under the main glacier outlets. The fluctuations in subglacial water routing occur even in the absence of external forcing. Based on these results we conclude that changes in the subglacial water routeways are an intrinsic part of the drainage basin dynamics, where the subglacial system is likely always in a transient state. The results also imply that fluctuations at the margins observed at present might originate from changes several hundred kilometres upstream. Since surface elevation changes may propagate upstream over timescales much longer than the observational period, the cause of the fluctuations may not be present in current observational records.

Greenland Ice Sheet: Higher Nonlinearity of Ice Flow Significantly Reduces Estimated Basal Motion

“…Since the stress exponent is a material property of ice, this observation is not restricted to GrIS but also applicable to the Antarctic Ice Sheet and mountain glaciers. Models that use n = 3 (Gillet-Chaulet et al, 2012;Graversen et al, 2011;Karlsson & Dahl-Jensen, 2015;Ren et al, 2011) may thus underestimate ice fluxes or may compensate for this by invoking basal motion. (i) Strong, centimeter-scale flow heterogeneity in ice is observed in numerical simulations of ice deformation ; using n = 3) and disturbances in layering in ice cores .…”

Limited Impact of Subglacial Supercooling Freeze‐on for Greenland Ice Sheet Stratigraphy

“…We use basal and surface digital elevation models (DEMs) from Morlighem et al () and Howat et al (), respectively, with grid sizes of 150 m. We restrict our subsequent analysis to the northern and central part of the ice sheet since the UDR identification was most successful in this region (Panton & Karlsson, ). We apply a basal sliding rate to GlaDS from Karlsson and Dahl‐Jensen (). In that study, the basal horizontal velocity ( u b ) was calculated based on a modeled value for the sliding coefficient k s (Weertman, ): where τ b is the basal shear stress assumed to be equal to the driving stress, and H is the ice thickness.…”

Enhanced Firn Densification in High‐Accumulation Shear Margins of the NE Greenland Ice Stream

“…At NEGIS, till is found both within and outside of streaming flow, so sediment availability likely does not set the boundary of fast flow (Christianson et al, ). Some basal water is likely present across the region; there is no evidence of extensive frozen regions (MacGregor et al, ), and previous studies have hypothesized that the distribution and flowpaths of water may, in part, control the location of the ice stream (Christianson et al, ; Karlsson & Dahl‐Jensen, ). We test this hypothesis by conducting a high‐resolution survey of ice and firn density across the ice stream, which affect subglacial hydropotential, and compare those results with previously published geophysical observations of water distribution beneath the ice stream.…”