Abstract
Abstract. Liquid water content (wetness) within glacier ice is known to strongly control ice viscosity and ice deformation processes. Little is known about wetness of ice on the outer flanks of the Greenland Ice Sheet, where a temperate layer of basal ice exists. This study integrates borehole and radar surveys collected in June 2012 to provide direct estimates of englacial ice wetness in the ablation zone of western Greenland. We estimate electromagnetic propagation velocity of the ice body by inverting reflection travel times from radar data. Our inversion is constrained by ice thickness measured in boreholes and by positioning of a temperate–cold ice boundary identified in boreholes. Electromagnetic propagation velocities are consistent with a depth-averaged wetness of ∼ 0.5–1.1 %. The inversion indicates that wetness within the ice varies from < 0.1 % in an upper cold layer to ∼ 2.9–4.6 % in a 130–150 m thick temperate layer located above the glacier bed. Such high wetness should yield high rates of shear strain, which need to be accounted for in glacial flow models that focus on the ablation zone of Greenland. This high wetness also needs to be accounted for when determining ice thickness from radar measurements.
Highlights
As ice flows outward from the centre of the Greenland Ice Sheet (GrIS), heat is added at the base of the ice column
The temperate basal layer present along the outer flanks of the GrIS arises from geothermal heating and flow mechanisms acting on cold ice moving outward from centre of the ice sheet
Our integration of ground-based radar data with information collected in boreholes reveals a two-layer thermo-hydrologic structure of varying thicknesses in the ablation zone of western Greenland
Summary
As ice flows outward from the centre of the Greenland Ice Sheet (GrIS), heat is added at the base of the ice column. Several ice sheet flow models depict that in western Greenland enough heat is eventually added to develop a fully temperate layer of basal ice Limited borehole temperature observations have confirmed a temperate basal layer in western Greenland that is tens of metres to well over 100 m thick (Lüthi et al, 2002; Ryser et al, 2014; Harrington et al, 2015). This layer potentially plays a key role in deformational motion of the ice sheet. Due to a lack of observational evidence for constraining the water content of the ice, poorly constrained modelling decisions must be made regarding the water content and viscosity of the GrIS temperate basal layer
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