Numerical reconstructions of the penultimate glacial maximum Northern Hemisphere ice sheets: sensitivity to climate forcing and model parameters

ABSTRACT Numerous ice-sheet reconstructions of the last glacial cycle have been proposed, however due to limited geological evidence, reconstructing older Northern Hemisphere ice sheets remains a difficult exercise. Here we focus on the penultimate glacial maximum (PGM; ~140 ka BP) over the Northern Hemisphere. While some evidence of the PGM Eurasian ice-sheet extent were found, this is not the case for the corresponding Laurentide ice sheet. To improve the glaciological reconstructions of the PGM Northern Hemisphere ice sheets, we explore the parameter space of ice-sheet model uncertainties and carry out numerous univariate ice-sheet steady-state sensitivity simulations. We use two PGM climate simulations to force the ice-sheet model, differing in the prescribed Laurentide ice topography (small and large). The simulated Northern Hemisphere ice volume ranges from 124.7 to 152 m SLE when using the climate accounting for a small Laurentide ice sheet, which is compatible with global sea-level reconstructions of this period (−92 to −150 m). Conversely, using the climate simulation with a Laurentide ice sheet comparable in size to that of the last glacial maximum results in too large ice volumes. Changes in basal drag provide the upper bound ice volume of our experiments, whereas changes in the distribution of ice streams provide the lower bound.