Project

Discipline

borehole; geophysics; stability; sliding; glacial hydraulics; ice deformation; numerical modeling; Glacier; Basal processes; Greenland; Ice Sheet; Dynamics

Lead
Lay summary
The Greenland Ice Sheet is losing mass at high and accelerating rates through increased surface melt, peripheral thinning and accelerated flow of outlet glaciers. 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 summerRouting 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 Greenland Ice Sheet. 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. 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.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Self-organised

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

The Greenland Ice Sheet (GrIS) is currently losing mass at a rate of 100-200Gt/a through increased surface melt, peripheral thinningand accelerated flow of outlet glaciers, thus contributing 0.3-0.6 mm/a to global sea level rise. While a consistentexplanation of the unprecedented, almost simultaneous acceleration of severallarge outlet glaciers is emerging, the situation is less clear for theobserved mass loss of the slower moving marginal areas. Ice dynamics of thesetemperate-based, slow-moving areas is highly susceptible to timing and amountof melt water discharge to the base of the ice sheet, leading to big andwidespread flow acceleration in summer.Routing of surface melt water to the base of the ice sheet affects the localsubglacial water pressure, leads to short term variations in ice-bed couplingand ice flow velocity, and thus affects mass transport and ice sheet geometryin the ablation area. Since the number of melt days and the area affected bysurface melt in summer have increased substantially over the last decade,concerns have arisen about the feedback of faster mass transport from the icesheet's interior to low elevations, more meltwater production, and thereforeincreasingly rapid mass loss from the ice sheet periphery.The aim of this project is a better understanding of the processes responsiblefor peripheral thinning and seasonal flow velocity variations of the marginalareas of the GrIS. In a coordinated international and interdisciplinaryeffort we will collect a unique body of \emph{in situ} measurements along aflow line in the ablation area downstream of Swiss Camp (West Greenland,indicated in Fig.~1). We will instrument boreholes to the bedrock to obtaininformation on processes at the ice-bedrock interface, the thermal structure,internal deformation and layering within the ice body. These data sets willbe complemented by high time-resolution measurements of surface motion,climate parameters, and seismicity. To investigate the short term dynamicresponse of the ice body to changes in the subglacial hydraulic system, wewill monitor diurnal cycles, and in addition disturb the subglacial waterpressure by routing water pulses of increasing magnitude into the boreholes.To interpret the collected data sets we will use models of surface melt andglacial hydraulics, and a 3D thermo-mechanically coupled ice dynamics model.With an inverse modeling approach we will attempt to quantify the dependenceof basal motion on stress state and water pressure. Such parametrizations arekey requisites for realistic and high resolution ice sheet models. Measuredquantities, such as ice temperatures and internal layering structures, willprovide benchmarks for high resolution dynamic models of the GrIS.This project is a joint effort with research partners from the USA who haveapplied for funding from the US National Science Foundation: Ginny Catania(University of Texas, Austin, TX), Robert Hawley (Dartmouth College, Hanover,NH) and Thomas Newmann (University of Vermont, Burlington, VT).