McGill paleoclimate model ice sheet sensitivity to ice flow rate and discharge parameters

Abstract.

Sensitivity studies of the ice-sheet model and forcing in the McGill Paleoclimate Model (MPM) are presented. The MPM is a five component (atmosphere, ocean, sea ice, land surface, ice sheet) sectorially averaged Earth system model of intermediate complexity (EMIC). An isothermal flow line model is employed for the ice sheet component, where the flow is considered to be exclusively in the meridional (north–south) direction. The formulation for the lateral (east–west) flux of ice into the ocean employs a lateral length scale for the ice sheets, which is parameterized by assuming the ice sheets to have a perfectly plastic behaviour in the east–west direction. The meridional flow of ice in the ice-sheet component depends on the temperature dependent flow parameter, or rate factor. A sensitivity study is performed on this parameter. The ice flow rate factor is found to have a large effect on both the ice volume and the extent of the southern margin. A sensitivity study is also performed on the east–west length scale of the ice sheets. Significant increases in both the ice volume and growth rate are obtained when this length scale is augmented. The bedrock relaxation time is shown to have a moderate effect on the growth rate of the ice sheets, but only after model year 35 ka. To improve the ice sheet-atmosphere coupling in the MPM, a high resolution nested land surface component is introduced. By calculating the land surface processes on the higher resolution of the ice-sheet component, a more accurate representation of the dependence of the surface air temperature on the surface elevation of the ice sheet can be included. This removes grid-related artifacts from the equilibrium ice sheets determined by the model. It is shown that this high-resolution nested component does not significantly affect the growth rate of the ice sheets during the initiation phase of glaciation.