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Ice-stream response to ocean tides and the form of the basal sliding law

This paper focuses on a puzzling observation of ice-stream motion that has so far remained unexplained. The flow of many a few large ice streams are known to display periodic changes, where velocities increase by about 10% over a span of one week and then decrease back to previous levels in the following week. Previous analysis has shown very clearly that these changes must be driven by the effect of ocean tides at the point where the ice begins to float on the ocean, but the exact mechanism of the interaction has remained unknown.

In this paper, a numerical model has been used to show that the velocity variations can only arise if the sediments beneath the ice stream deform in a particular way, becoming increasingly stiff as they are forced to deform quickly. The model allows clear constraints to be put on the relationship between stress and deformation in the sediments. Beyond providing an explanation for a puzzling set of observations, this finding also has a much wider significance. The demonstration that sub-glacial sediments have these ‘non-linear’ properties, will allow us to improve the way that ice streams are represented in the continental-scale ice-sheet models that we use to project the future of the Antarctic Ice Sheet. These are the models that are used to predict the contribution Antarctica and Greenland will make to sea-level rise in future decades and centuries.

Link to the full paper in the NERC Open Research Archive


Gudmundsson, G.H. 2011.


Cryosphere, 5, No. 1, 59-270