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 three-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 localisation may be controlled by preferential meltwater infiltration in topographic dips between ogives.
Highlights
In many parts of the world, glaciers have recently slowed down as they thinned (Heid and Kääb, 2012; Dehecq et al, 2019)
Bowdoin Glacier (Kangerluarsuup Sermia) is a tidewater glacier located in northwestern Greenland
The glacier was chosen for fieldwork due to its accessibility, and the previously observed propagation of the mass loss of the Greenland Ice Sheet from the south to the northwest (Khan et al, 2010), the more recent satellite gravimetry data shows that virtually all margins of the Greenland Ice Sheet are loosing mass (Groh and Horwath, 2016)
Summary
In many parts of the world, glaciers have recently slowed down as they thinned (Heid and Kääb, 2012; Dehecq et al, 2019). Around the margins of the Greenland Ice Sheet, marine-terminating outlet glaciers have thinned, but they have accelerated and retreated faster than any of its other parts (e.g., Krabill et al, 2000; Rignot and Kanagaratnam, 2006; Pritchard et al, 2009; Moon et al, 2012, 2015; Hill et al, 2017), significantly impacting the total mass loss of the ice sheet (e.g., Enderlin et al, 2014; Khan et al, 2015; McMillan et al, 2016). Longitudinal stress coupling becomes apparent through the upstream propagation of tidal velocity variations (Walters, 1989; Walter et al, 2012; Sugiyama et al, 2014; Podolskiy et al, 2017; Seddik et al, 2019) In such conditions, the increased flow velocities and longitudinal stretching are largely controlled by the ice viscosity. Numerical models show that such differences in ice viscosity influence the flow and shape of entire glaciers and ice sheets (e.g., Figures 2, 7 of Seguinot et al, 2016)
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