ALBERT

Description: Previous modelling efforts have investigated climate responses to different Milankovitch forcing during Marine Isotope Stage (MIS) 13. During this time the climate has been highly variable at atmospheric CO2 concentrations of ~240 ppm. As yet, ice sheet-climate feedbacks were missing in previous studies. Therefore we use the state-of-the-art coupled climate-ice sheet model, AWI-ESM-1.2, to investigate the MIS-13 climate and corresponding Northern Hemisphere ice sheet (NHIS) evolution by performing simulations under three different astronomical configurations representing 495, 506 and 517 kyr BP. The simulated excess ice compared to present-day is mainly over the Cordillera, Arctic islands and Tibet. The global mean surface air temperature for the MIS-13 experiments have the same magnitude. At 506 kyr BP with boreal summer at perihelion, the Northern Hemisphere continents are warmer during summer than the other experiments, which could potentially inhibit the development of the ice sheets. The Cordilleran Ice Sheet is found to be especially sensitive to orbital (precession) forcing, at an intermediate CO2 level. This is probably due to its high elevation where the freezing point could be easily maintained. The other ice sheets over northeast America and Eurasia, however, are absent in our simulations. We propose that the alpine-based Cordilleran Ice Sheet is more sensitive and easier to build up than other NHISs in response to the astronomical controlled summer insolation. Dynamic surges are simulated for the Cordilleran Ice Sheet under fixed low orbital forcing. These surges due to internal ice sheet-climate feedbacks could potentially be the mechanism for the millennial scale H-like events.