Interactions between ocean circulation and the Northern Hemisphere ice sheets at 40 ky B.P. in an Earth System Model (iLOVECLIM-GRISLI)

During the last glacial period, the climate went through rapid fluctuations together with changes in ocean circulation and ice sheets volume accompanied by iceberg discharges. These rapid climate variations, namely Dansgaard-Oeschger events, are still not fully explained. This study’s aim is to contribute to their better understanding, focusing on interactions between ice sheets and ocean circulation. To this end, we use the iLOVECLIM-GRISLI coupled climate-ice sheet model and run two different perturbation experiments related to the ice sheet and ocean components. Starting from a quasi equilibrium corresponding to 40 ky B.P. greenhouse gas concentration, incoming solar radiation and ice sheet volume, the first experiment consists in imposing either constant or amplified sub-shelf melt rates in comparison with the control simulation. In the second experiment, we focus on the interface between the ice sheets and the bedrock. The basal friction coefficient values are imposed following the same procedure. These two experiments are similar to freshwater hosing experiments but here the water comes directly from the interactively computed ice sheets change. For each experiment, the perturbation is imposed for 500 years before returning to the unperturbed conditions for one thousand years and its impacts on the climate system are investigated. Our results highlight feedbacks that may help to explain the abrupt nature of the climate transitions observed during the last glacial period.