Toward Improved Understanding of Changes in Greenland Outlet Glacier Shear Margin Dynamics in a Warming Climate

Abstract

The Greenland Ice Sheet has experienced accelerated mass loss over the last couple decades, in part due to destabilization of marine-terminating outlet glaciers. Retreat and acceleration of outlet glaciers coincides with atmospheric and oceanic warming resulting in a significant contribution to sea-level rise. The relative role of surface meltwater production, runoff and infiltration on the dynamics of these systems is not well-understood. To assess how surface meltwater impacts shear margin dynamics and regional ice flow of outlet glaciers, we investigate the impact of basal lubrication of Jakobshavn Isbrae shear margins due to drainage from water-filled crevasses. We map the areal extent of inundated crevasses during summer (May-August) from 2000 to 2012 using satellite imagery and determined an increasing trend in the total areal extent over this time interval. We use a numerical ice flow model to quantify the potential impact of weakened shear margins due to surface melt derived basal lubrication on regional flow velocities. Ice flow velocities 10 km from the lateral margins of Jakobshavn were amplified by as much as 20%, resulting in an increase of ∼0.6 Gt yr −1 in ice-mass discharge through the shear margins into the ice stream. Under future warming scenarios with increased surface melt ponding, simulations indicate up to a 30% increase in extra-marginal ice flow. We conclude that surface meltwater will likely play an important role in the evolving dynamics of glacier shear margins and the future mass flux through Greenland's major marine-terminating outlet glaciers.

Controls on Water Storage and Drainage in Crevasses on the Greenland Ice Sheet

“…The full dynamic consequences of such events are explored in detail elsewhere (e.g., Nienow et al, 2017), but it is apparent that meltwater inputs to the bed that are rapid (Schoof, 2010) and spatially discrete (Banwell et al, 2016) can influence ice dynamics. For example, rapidly draining crevasse systems at the shear margin of Jakobshavn Isbrae have been shown to deliver meltwater to the bed at sufficient rates and volumes to overwhelm the capacity of the subglacial system (Lampkin et al, 2013), increasing ice mass flux across the shear margin and enhancing glacier discharge (Cavanagh et al, 2017;Lampkin et al, 2018).…”

Tidal Modulation of a Lateral Shear Margin: Priestley Glacier, Antarctica

“…More generally, shear margins form wherever there is a boundary between ice that is deforming rapidly, and ice or rock, that is not (Echelmeyer et al, 1994;Jackson and Kamb, 1997;Whillans and van der Veen, 1997). Changes in shear margin properties have been associated with climate-driven changes in the flow of Greenland and West Antarctic outlet glaciers (Cavanagh et al, 2017;Lampkin et al, 2018;Alley et al, 2019). The mechanics of lateral margins are thus important to both ice-sheet system dynamics and to the representation of marine-terminating glacial systems in models used to project future change.…”