Subglacial Controls on the Short Term Dynamics at the Margins of the Greenland Ice Sheet

The Greenland Ice Sheet (GrIS) is losing mass at a rate of 100-200 Gt/a through increased surface melt, peripheral thinning and accelerated flow of outlet glaciers, thus contributing 0.3-0.6 mm/a to global sea level rise. While a consistent explanation of the unprecedented, almost simultaneous acceleration of several large outlet glaciers is emerging, the situation is less clear for the observed mass loss of the slower moving marginal areas. Ice dynamics of these temperate-based, slow-moving areas is highly susceptible to timing and amount of melt water discharge to the base of the ice sheet, leading to big and widespread flow acceleration in summer.

Routing of surface melt water to the base of the ice sheet affects the local subglacial water pressure, leads to short term variations in ice-bed coupling and ice flow velocity, and thus affects mass transport and ice sheet geometry in the ablation area. Since the number of melt days and the area affected by surface melt in summer have increased substantially over the last decade, concerns have arisen about the feedback of faster mass transport from the ice sheet’s interior to low elevations, more meltwater production, and therefore increasingly rapid mass loss from the ice sheet periphery.

The aim of this project is a better understanding of the processes responsible for peripheral thinning and seasonal flow velocity variations of the marginal areas of the GrIS. In a coordinated international and interdisciplinary effort we will collect a unique body of in situ measurements along a flow line in the ablation area downstream of Swiss Camp (West Greenland). We will instrument boreholes to the bedrock to obtain information on processes at the ice- bedrock interface, the thermal structure, internal deformation and layering within the ice body. These data sets will be complemented by high time-resolution measurements of surface motion, climate parameters, and seismicity. To investigate the short term dynamic response of the ice body to changes in the subglacial hydraulic system we will monitor the diurnal cycle, and additionally disturb the subglacial water pressure by routing water pulses of increasing magnitude into the boreholes.

To interpret the collected data sets we will use models of surface melt and glacial hydraulics, and a 3D thermo-mechanically coupled ice dynamics model. With an inverse modeling approach we will attempt to quantify the dependence of basal motion on stress state and water pressure. Such parametrizations are key requisites for realistic and high resolution ice sheet models. Measured quantities, such as ice temperatures and internal layering structures, will provide benchmarks for high resolution dynamic models of the GrIS.

Collaboration:

Prof. Dr. Ginny Catania (University of Texas, Austin, TX)

Dr. Robert Hawley (Dartmouth College, Hanover, NH)

Dr. Thomas Neumann (NASA Goddard SFC, Greenbelt, MD).

Matthew Hoffman (Los Alamos National Labs)