Modeling Northern Hemisphere ice-sheet distribution during MIS 5 and MIS 7 glacial inceptions

Abstract

The present manuscript compares Marine Iso- tope Stage 5 (MIS 5, 125–115 kyr BP) and MIS 7 (236– 229 kyr BP) with the aim to investigate the origin of the difference in ice-sheet growth over the Northern Hemi- sphere high latitudes between these last two inceptions. Our approach combines a low resolution coupled atmosphere– ocean–sea-ice general circulation model and a 3-D thermo- mechanical ice-sheet model to simulate the state of the ice sheets associated with the inception climate states of MIS 5 and MIS 7. Our results show that external forcing (orbitals and GHG) and sea-ice albedo feedbacks are the main fac- tors responsible for the difference in the land-ice initial state between MIS 5 and MIS 7 and that our cold climate model bias impacts more during a cold inception, such as MIS 7, than during a warm inception, such as MIS 5. In addition, if proper ice-elevation and albedo feedbacks are not taken into consideration, the evolution towards glacial inception is hardly simulated, especially for MIS 7. Finally, results high- light that while simulated ice volumes for MIS 5 glacial in- ception almost fit with paleo-reconstructions, the lack of pre- cipitation over high latitudes, identified as a bias of our cli- mate model, does not allow for a proper simulation of MIS 7 glacial inception.