Basal Mechanics of Marine Ice Sheets

Marine-based ice sheets like the West Antarctic Ice Sheet, whose beds are below sea level, are potentially unstable due to the possibility of rapid retreat of their grounding lines, where ice lifts off from their beds. Due to the catastrophic loss of ice into the ocean that would result from such a scenario, this process of grounding-line retreat is therefore crucial to understand if one is to be able to predict how much sea level rise there will be in the future. One important aspect of this is understanding not only how the ice deforms, but how it slides over its bed. Experimental evidence supports the fact that friction within granular tills underlying ice sheets becomes important in the near-flotation portions of ice sheets, but such frictional behavior has not been commonly included in ice sheet models to predict ice sheet stability. We address this question of how ice sheet profiles and ice sheet stability are modified with an improved model for basal sliding that includes friction. We find that stable parts of the ice sheet are generally more stable, but that unstable parts are more unstable than previous models would predict, and that ice sheets are more sensitive to climate perturbations (Tsai et al. 2015). See publications for more details.

The plot at right schematically shows a marine-based ice sheet that flows (from left to right) into the ocean. The main forces at play are gravity ('gravitational driving stress', gray), basal drag ('basal shear stress', red) and forces related to the stretching of ice ('extensional stress divergence', green). As shown schematically with the colored arrows in the insets, the inclusion of a standard 'Coulomb' friction on top of the standard 'power law' basal drag results in a different force balance in the region close to the grounding line. These differences in the force balance cause ice sheet stability to be significantly different.