Role of ice sheet topography change during the last deglaciation: effect of winds and thermal forcing on the AMOC stability

One major aspect of climate change during the last deglaciation is that abrupt climate events occurred superimposed on gradual warming. Such abrupt changes took place as climate forcing as insolation, greenhouse gases, ice sheet and associated meltwater was evolving. This is the case for the BllingAllerd (BA) event (about 14.7 / 14.2 ka), associated with an abrupt recovery of the Atlantic Meridional Overturning Circulation (AMOC), warming of northern high latitudes and cooling of the southern high latitudes. The BA is then followed by the Younger-Dryas cooling, characterized by a significant drop in the temperature in the Northern Hemisphere and weakening of the AMOC. One way to characterize the occurrence and the stability of abrupt event is to use transient simulations with Atmosphere-Ocean general circulation model. Obase and Abe-Ouchi (2019) realized transient experiment using MIROC4m with time-dependent orbital parameters, greenhouse gases and fixed ice sheet topography (at 21ka). The authors were able to demonstrate that abrupt event associated with BA occurs due to the gradual warming, with no meltwater reduction. Here, as a more realistic study, and in the direct continuation of the previous one, we carried out transient experiments with MIROC4m using in addition time-dependent ice sheet topography. Indeed, gradual retreat of the Northern Hemisphere ice sheet (both Northern America and Northern Eurasia) is known to affect thermodynamically the North Atlantic deep -water formation (i.e. AMOC). Our main findings are: BA like abrupt event still occurs, associated with an AMOC recovery, at about 14.7 ka. The onset of the event is very close to Greenland warming as recorded by proxy-based data, with a similar amplitude (+10°C). Retreat of the Northern Hemisphere ice sheet induce winds change (decrease between 15 and 13 ka) and temperature change over North Atlantic compared to Obase and Abe-Ouchi. Winds change is responsible of the abrupt weakening of the AMOC by enabling coverage of the convection areas by Arctic sea-ice. This indicate that wind reduction is more important than warming for AMOC stability.