The impact of spatially varying ice sheet basal conditions on sliding at glacial time scales

Spatially variable bed conditions govern how ice sheets behave at glacial time scales (>1000 years). The presence or lack of complete sediment cover is responsible for changes in dynamics between the core and peripheral regions of the Laurentide and Fennoscandian ice sheets. A key component of this change is because sliding is promoted when unconsolidated sediments below the ice become water saturated, and become weaker than the overlying ice. We present an ice sheet sliding module for the Parallel Ice Sheet Model (PISM) that takes into account changes in sediment cover. This model routes meltwater, derived from the surface and base of the ice sheet, towards the margin of the ice sheet. The sliding is accomplished through water saturated sediments, or through hard-bedded sliding induced by changes in the effective pressure in the water drainage system. In areas with continuous, water saturated sediments, sliding is almost always accomplished through sediment deformation, except during times of high discharge. In areas with even a small portion of bare rock, sliding is dependent on the seasonally changing supply of water. Our model causes a more rapid buildup of ice sheets compared to a sediment-deformation only model, especially into areas with complete sediment cover.