Basal conditions of Denman Glacier from glacier hydrology and ice dynamics modeling

Abstract. Basal sliding in Antarctic glaciers is often modeled using a friction law that relates basal shear stresses to the effective pressure. As few ice sheet models are dynamically coupled to subglacial hydrology models, variability in subglacial hydrology associated with the effective pressure is often implicitly captured in the friction coefficient – an unknown parameter in the friction law. We investigate the impact of using effective pressures calculated from the Glacier Drainage System (GlaDS) model on friction coefficients calculated using inverse methods in the Ice-sheet and Sea-level System Model (ISSM) at Denman Glacier, East Antarctica, for the Schoof and Budd friction laws. For the Schoof friction law, a positive correlation emerges between the GlaDS effective pressure and friction coefficient in regions of fast ice flow. Using GlaDS effective pressures generally leads to smoother friction coefficients and basal shear stresses, and smaller differences between the simulated and observed velocities, compared with using an effective pressure equal to the ice overburden pressure plus the gravitational potential energy of the water. Compared with the Budd law, the Schoof law offers improved capabilities in capturing the spatial variations associated with known physics of the subglacial hydrology. Our results indicate that ice sheet model representation of basal sliding is more realistic when using direct outputs from a subglacial hydrology model, demonstrating the importance of coupling between ice sheet and subglacial hydrological systems. However, using our outputs we have also developed an empirical parameterization that improves application of the Schoof law without requiring explicit hydrological modeling.