The impact of the friction law on coupled ice flow/subglacial hydrology modeling

Basal sliding is a key component of ice motion that is implemented in ice flow models via the use of a friction law, a relation between the basal shear stress, basal sliding velocity, and the effective pressure. Recent studies have performed two-way coupling between two-dimensional subglacial hydrology models with inefficient and efficient drainage components, and ice flow models via the effective pressure in the friction law. However, to date, there has not been an investigation of the impact of the friction law on two-way coupled ice flow/subglacial hydrology modeling. Here, we examine the effect of the Budd friction law, the Schoof friction law, and two regularized-Coulomb friction laws that we develop, on coupled modeling in the Siple Coast of West Antarctica. We found that when using the Budd friction law, the basal shear stress failed to respond to changes in both ice speed and effective pressure in a fashion that was consistent with the state of the subglacial hydrologic system, and the Schoof friction law did not accurately estimate the state of the subglacial hydrologic system. Consequently, using the Budd and Schoof friction laws led to instabilities in ice motion and flooding of the subglacial hydrologic system due to dynamic thinning of ice. The new friction laws we developed ensured an accurate estimation of the state of the subglacial hydrologic system, and no such instabilities arose in the corresponding simulations.