Modelling Greenland Ice Sheet inception and sustainability during the Late Pliocene

Understanding the evolution and dynamics of ice sheet growth during past warm periods is a very important topic considering the potential total removal of the Greenland ice sheet in the future. In this regard, one key event is the full glaciation of Greenland that occurred at the end of the Pliocene warm period, but remains partially unexplained. Previous modelling studies succeeded in reproducing this full glaciation either by imposing an unrealistically low CO2 value or by imposing a partial ice sheet over the surface of Greenland. Although highlighting some fundamental mechanisms, none of these studies are fully satisfactory because they do not reflect realistic conditions occurring during the Late Pliocene. Through a series of simulations with the coupled climate model IPSL-CM5A used to force the ice sheet model GRISLI, we show that a drop in CO2 does not lead to an abrupt inception of the Grenland Ice Sheet (GrIS). High ablation rates in Central and North Greenland combined with low accumulation prevent such an abrupt inception. Ice sheet inception occurs when combining low summer insolation and CO2 levels below modern values, the GrIS being restricted to the Southeast region where high topography favors this build-up. This ice sheet experiences only partial melting during summer insolation maxima combined with high CO2. Further growth of the ice sheet with recoupling experiments is important at 360 ppm and 280 ppm during insolation minima. Thus, the full glaciation at 2.6 Ma could be the result of a cumulative build-up of the GrIS over several orbital cycles, leading to progressively more intense glaciations during low summer insolation periods. Although this result could be a shortcoming of the modeling framework itself, the gradual glacial inception interpreted from the oxygen isotope record could support our scenario.