Abstract
Future projections of global mean sea level change are uncertain, partly because of our limited understanding of the dynamics of Greenland’s outlet glaciers. Here we study Nioghalvfjerdsbræ, an outlet glacier of the Northeast Greenland Ice Stream that holds 1.1 m sea-level equivalent of ice. We use GPS observations and numerical modelling to investigate the role of tides as well as the elastic contribution to glacier flow. We find that ocean tides alter the basal lubrication of the glacier up to 10 km inland of the grounding line, and that their influence is best described by a viscoelastic rather than a viscous model. Further inland, sliding is the dominant mechanism of fast glacier motion, and the ice flow induces persistent elastic strain. We conclude that elastic deformation plays a role in glacier flow, particularly in areas of steep topographic changes and fast ice velocities.
Highlights
Future projections of global mean sea level change are uncertain, partly because of our limited understanding of the dynamics of Greenland’s outlet glaciers
Several logical questions arise: Are the crevasse fields located in regions in which elastic strains and stresses do not decline due to stress changes? Could a viscoelastic model provide novel insights into the role of elastic strains and stresses in Greenland’s outlet glaciers? So far, observations of the elastic effects have primarily been focusing on tides: In Antarctica, it has been shown that tides can alter glacier flow up to 80 km upstream of the grounding line of large ice streams[20,23,24,25,26,27]
For the 79°NG, an outlet glacier of the Northeast Greenland Ice Stream (NEGIS), we first analyse the influence of tides on glacier flow (Fig. 1)
Summary
Future projections of global mean sea level change are uncertain, partly because of our limited understanding of the dynamics of Greenland’s outlet glaciers. We study Nioghalvfjerdsbræ, an outlet glacier of the Northeast Greenland Ice Stream that holds 1.1 m sealevel equivalent of ice. We use GPS observations and numerical modelling to investigate the role of tides as well as the elastic contribution to glacier flow. Ocean tides modulate the water pressure at the grounding line resulting in short-term changes of basal stress. These short-term stress changes are likely transmitted inland and impact the ice dynamics upstream[20]. Inversion of observed surface velocities provides the friction coefficient field Based on these results, we show that ocean tides change the ice flow only a few kilometres upstream of the grounding line at 79°NG. We propose ideas for future modelling work
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