Evaluating seasonal sea-ice cover over the Southern Ocean at the Last Glacial Maximum

Simulations and paleo-proxy records suggest a fairly well-constrained glacial winter sea-ice edge between 50.5 and 51 degrees S. However, the spread in simulated glacial summer seaice is wide, ranging from almost ice-free conditions to a seaice edge reaching 53 degrees S. Combining model outputs and proxy data, we estimate a likely LGM summer sea-ice edge between 61 and 62 degrees S and a mean summer sea-ice extent of 14-15 x 10(6) km(2) , which is similar to 20 %similar to 30 % larger than previous estimates.

These estimates point to a higher seasonality of southern hemispheric sea-ice during the LGM than today. We also analyze the main processes defining the summer sea-ice edge within each of the models. We find that summer sea-ice cover is mainly defined by thermodynamic effects in some models, while the sea-ice edge is defined by the position of Southern Ocean upwelling in others.

For models included in both PMIP3 and PMIP4, this thermodynamic or dynamic control on sea-ice is consistent across both experiments. Finally, we find that the impact of changes in large-scale ocean circulation on summer sea-ice within a single model is smaller than the natural range of summer sea-ice cover across the models considered here. This indicates that care must be taken when using a single model to reconstruct past climate regimes.