A numerical study on cyclic behaviour of polar ice sheets

Possible cyclic behaviour of polar ice sheets is studied with a numerical ice-flow model. The model includes a calculation of bedrock adjustment and temperature field in the ice sheet. Basal water is traced and affects ice-mass discharge. Relaxation oscillations occur only for low ice-accumulation rates (less than 5 cm ice depth per year). For larger ice-accumulation rates, 2 steady-state regimes exist, depending on temperature: an ice sheet frozen to the bottom, and an ice sheet subject to basal melting every where. The volume of the latter is considerably smaller (about 65% of that of the “cold sheet”). In general, the mean basal ice temperature decreases with increasing ice accumulation rate. This is due to the advection term in the heat equation (which has been ignored in earlier studies of ice-sheet surging).