Ice sheet grounding zone stabilization due to till compaction

K. Christianson, B. R. Parizek, R. B. Alley, H. J. Horgan, R. W. Jacobel, S. Anandakrishnan, B. A. Keisling, B. D. Craig, and A. Muto

Geophysical Research Letters (28 October 2013)

DOI: 10.1002/2013GL057447

Based on modeling motivated by new GPS and radio-echo sounding surveys, a few-kilometers-long zone of Whillans Ice Stream, West Antarctica, just inland of the grounding line has higher basal shear stress than the ice farther upstream or the freely slipping ice shelf downstream. Data from this zone show a few-meter-high upwarp of the surface overlying a large fold extending through all internal radar layers observed. Flowband modeling shows that the fold can be generated by decreased basal lubrication beneath the upwarp. Basal topography alone cannot create this fold. Physical modeling and available data suggest that low-amplitude tidal flexure of the ice shelf extends a few kilometers inland. Downward flexing of this grounded ice from the rising tide would compact subglacial till, resulting in higher basal shear stress. This result suggests that important processes influencing grounding line stability are not included in modern whole-ice-sheet models.

keywords: ice stream; ice shelf; tidal flexure; subglacial hydrology; radio-echo sounding; glacier dynamics; 0726 Ice sheets; 0730 Ice streams; 0728 Ice shelves; 0774 Dynamics; 0776 Glaciology

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