We present simulations of the Northern Hemisphere land ice through the last glacial-interglacial cycle with a vertically integrated ice-sheet model and a three-dimensional thermomechanical ice-sheet model. Both models are coupled asynchronously to the zonally averaged Louvain-la-Neuve climate model, which includes simplified treatments of the atmosphere, ocean and sea ice. The two-dimensional vertically integrated ice-sheet model, which contains no thermomechanical coupling, was developed in spherical coordinates (Marsiat, 1994). The three-dimensional thermomechanical ice-sheet model was developed using the two-dimensional vertically integrated model as source.
We compare results of the vertically integrated with those of the thermomechanical ice-sheet model. in the thermomechanical model the deformation properties of ice depend on the temperature within the ice and the enhancement factor; the latter is introduced to model, in a simplified approach, the different flow properties of Pleistocene and Holocene ice due to varying dust content. The computations with the thermomechanical model show that the growth and decay of the Northern Hemisphere ice sheets can be modelled with a common enhancement factor for all ice sheets. It is shown that there are model set-ups for the thermomechanical model yielding temporal developments of the total ice volume comparable to those of the vertically integrated model. Furthermore, we demonstrate that for the coupled climate/cryosphere system the total ice volume depends considerably on the enhancement factor.