Abstract
Measurements of ice temperature provide crucial constraints on ice viscosity and the thermodynamic processes occurring within a glacier. However, such measurements are presently limited by a small number of relatively coarse-spatial-resolution borehole records, especially for ice sheets. Here, we advance our understanding of glacier thermodynamics with an exceptionally high-vertical-resolution (~0.65 m), distributed-fiber-optic temperature-sensing profile from a 1043-m borehole drilled to the base of Sermeq Kujalleq (Store Glacier), Greenland. We report substantial but isolated strain heating within interglacial-phase ice at 208 to 242 m depth together with strongly heterogeneous ice deformation in glacial-phase ice below 889 m. We also observe a high-strain interface between glacial- and interglacial-phase ice and a 73-m-thick temperate basal layer, interpreted as locally formed and important for the glacier's fast motion. These findings demonstrate notable spatial heterogeneity, both vertically and at the catchment scale, in the conditions facilitating the fast motion of marine-terminating glaciers in Greenland.
Highlights
Mass loss from the Greenland Ice Sheet (GrIS) has increased sixfold since the 1980s and is the single largest cryospheric contributor to global sea-level rise [1, 2]
We installed a distributed temperature sensing (DTS) system on 5 July 2019 in a 1043-m hot-water drilled borehole located at site R30 on Store Glacier (70.57°N, 50.09°W; Fig. 1), where surface ice motion is ~600 m a−1
The Store Glacier temperature profile at R30 (Fig. 2A) is broadly consistent with theoretical estimates of ice temperature governed by advection—which in glaciers such as Store brings cold ice from high elevations to warmer settings at lower elevations—and vertically directed diffusion [15]
Summary
Mass loss from the Greenland Ice Sheet (GrIS) has increased sixfold since the 1980s and is the single largest cryospheric contributor to global sea-level rise [1, 2]. A crucial but scarce source of information comes from boreholes, which provide unambiguous records of subsurface ice properties, such as temperature profiles, deformation rates, and the conditions at the bed that influence basal motion. These records are especially relevant for Greenland’s marine-terminating glaciers, which flow rapidly (≥200 m a−1) through englacial deformation and basal motion [7]. GrIS models often rely on physical constraints from theoretical considerations or from studies conducted on smaller and more accessible glaciers elsewhere, which may not be representative of larger or faster ice masses [e.g. [11, 12]]
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