Englacial Warming Indicates Deep Crevassing in Bowdoin Glacier, Greenland

Abstract

All around the margins of the Greenland Ice Sheet, marine-terminating glaciers have recently thinned and accelerated. The reduced basal friction has yielded increased flow velocity, while the rate of longitudinal stretching has been limited by ice viscosity, which itself critically depends on temperature. However, ice temperature has rarely been measured on such fast-flowing and heavily crevassed glaciers. Here, we present a 3-year record of englacial temperatures obtained 2 (in 2014) to 1 km (in 2017) from the calving front of Bowdoin Glacier (Kangerluarsuup Sermia), a tidewater glacier in northwestern Greenland. Two boreholes separated by 165 (2014) to 197 m (2017) show significant temperature differences averaging 2.07 • C on their entire depth. Englacial warming of up to 0.39 • C a −1 , an order of magnitude above the theoretical rate of heat diffusion and viscous dissipation, indicates a deep and local heat source within the tidewater glacier. We interpret the heat source as latent heat from meltwater refreezing in crevasses reaching to, or near to, the bed of the glacier, whose localization may be controlled by preferential meltwater infiltration in topographic dips between ogives.

Thermodynamics of a fast-moving Greenlandic outlet glacier revealed by fiber-optic distributed temperature sensing

“…The energy input and sink required to sustain the anomaly can be used to estimate the deformation rate. Strain heating, Q s , is expressed as , where τ is the deviatoric stress tensor and is the strain rate tensor ( 10 , 16 ). Stress and strain are related via ( 44 , 45 ), where τ e is the effective stress and , and A is the creep parameter, which we take as 7.7 × 10 −25 s −1 Pa −3 following aggregate values in Cuffey and Paterson [( 16 ), table 3.3] with the range 6.7 × 10 −25 to 8.7 × 10 −25 s −1 Pa −3 , used to test parameter sensitivity and the flow exponent n ≈ 3.…”

“…The energy input and sink required to sustain the anomaly can be used to estimate the deformation rate. Strain heating, Q s , is expressed as Q s = tr( ̇ ) , where  is the deviatoric stress tensor and ̇ is the strain rate tensor (10,16). Stress and strain are related via ̇ = A  e n−1  (44,45), where  e is the effective stress and τ e 2 = 1 _ 2 tr(  2 ) , and A is the creep parameter, which we take as 7.…”

“…Such glaciers drain most of the ice sheet ( 2 , 8 ), yet they are rarely the subject of borehole investigations due to logistical challenges including pervasive crevassing and high strain rates that damage installed equipment [e.g. ( 7 , 9 , 10 )]. As a consequence, 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.…”

The cooling signature of basal crevasses in a hard-bedded region of the Greenland Ice Sheet

“…Moulins have been shown to migrate horizontally with depth (Holmund, 1988), which could possibly avoid this objection; however, numerous moulins would be needed to generate the cooling we observe in multiple boreholes. In the ablation zone surrounding Issunguata Sermia, active moulins have a mean density of 0.1 per square kilometer (Smith et al, 2015), and Catania and Neumann (2010) found relict moulins to be spaced ∼ 1 km apart, which suggests that it is unlikely that multiple moulins have thermally altered the instrumented block of ice with a surface area of ∼ 0.125 km 2 .…”

Thinning leads to calving-style changes at Bowdoin Glacier, Greenland

“…1a). Field campaigns on Bowdoin Glacier were repeated in the summers of 2013-2017 and 2019 in a collaboration between Hokkaido University, ETH Zurich and University of Florence (Podolskiy et al, 2017;Seguinot et al, 2020).…”