Last Glacial Maximum ice sheet impacts on North Atlantic climate variability: The importance of the sea ice lid



[1] Last Glacial Maximum (LGM) ICE-5G (VM2), ICE-6G (VM5a), and Paleoclimate Modelling Intercomparison Project Phase 3 ice sheet reconstructions are employed in high-resolution coupled climate model simulations to investigate the changes they induce in North Atlantic climate variability. An initial ICE-5G (VM2) experiment develops a rapid increase of sea ice extent once a thermal threshold is exceeded in this multimillennial simulation. Subpolar sea ice concentration and thickness are found to be strongly impacted by topographically induced downstream thermal effects from the Laurentide Ice Sheet in each of the reconstructions. However, in the two additional LGM perturbation experiments, the modeled changes in sea ice area are sufficiently similar to the LGM ICE-5G (VM2) experiment to lead to an equilibrium Atlantic Meridional Overturning Circulation strength that is also reduced by the same ~40% from preindustrial even though we find significant variation among the models in the deep convection regions of the subpolar glacial North Atlantic. Model-predicted sea ice concentrations in this critical region exceed those based upon multiproxy reconstructions, and we trace these significant differences to the intensity of the interannual variability of sea ice cover predictions.