Large ensemble simulations of the North American and Greenland ice sheets at the Last Glacial Maximum with a coupled atmospheric general circulation-ice sheet model

Abstract. The Last Glacial Maximum (LGM) is characterised by huge ice sheets covering the Northern Hemisphere, especially over North America, and by its cold climate. Numerical simulations of the climate and ice sheets of the LGM have been performed to better understand these systems, however the inherent uncertainty and sensitivity in the simulations to the selection of model parameters remain uncertain. Here, we perform a 200-member ensemble of simulations of the North American and Greenland ice sheets and climate of the LGM with an ice sheet-atmosphere-slab ocean coupled model (FAMOUS-BISICLES) to explore sensitivities of the coupled climate-ice system to 16 uncertain parameters. In the ensemble of simulations, the global temperature is primarily controlled by the combination of parameters in the large-scale condensation scheme and the cumulus convection scheme. In simulations with plausible LGM global temperatures, we find that the albedo parameters have only a small impact on the Greenland ice volume due to the limited area of surface ablation associated with the cold climate. Instead, the basal sliding law controls the ice volume by affecting ice transport from the interior to the margin. On the other hand, like the Greenland ice sheet in future climate change, the LGM North American ice sheet volume is controlled by parameters in the snow and ice albedo scheme. Few of our simulations produce an extensive North American ice sheet when the global temperature is above 12 °C. Based on constraints on the LGM global temperature, the ice volume and the southern extent of the North American ice sheet, we select 16 acceptable simulations. These simulations lack the southern extent of ice compared to reconstructions, though show reasonable performance on the ice sheet configuration and ice streams facing the Baffin Bay and the Arctic Ocean. The strong sensitivities of the North American ice sheet to albedo at the LGM may imply a potential constraint on the future Greenland ice sheet by constraining the albedo schemes.