Ice sheet grounding zone stabilization due to till compaction

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. Key Points Radar data depict the grounding line and associated internal layer folding Fold in radar internal layers can be explained by enhanced basal friction Enhanced friction is likely due to till compaction from tidal flexure