North American Ice Sheet reconstructions at the Last Glacial Maximum

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The areal extent of the last glacial maximum (LGM) ice sheets is well known in North America, but there is no direct geological proxy for ice sheet thickness or volume. Uncertainties associated with glaciological and geophysical reconstructions give widely varying estimates of North American Ice Sheet (NAIS) volume at LGM. In an effort to quantify the uncertainty associated with glaciological reconstructions, we conducted a suite of 190 numerical simulations of the last glacial cycle in North America, prescribing different climatic, mass balance, glaciologic, and isostatic treatments for the least constrained model variables. LGM ice sheet reconstructions were evaluated using the well-established geologic record of ice sheet area and southern extent at LGM ( Dyke and Prest (1987)). These constraints give a subset of 33 simulations that produce reasonable LGM ice cover in North America. Ice sheet dispositions and the associated parameter settings in this subset of tests provide insight into the plausible range of NAIS thickness, form, and mass balance regime at LGM. Ice volume in this subset of tests spans a range of 28.5–38.9×10 15 m 3 at LGM, with a predominant cluster at 32–36×10 15 m 3 . Taking floating ice and displaced continental water into account, this corresponds to 69–94 m eustatic sea level (msl). More than 75% of the accepted tests fall in the range 78–88 msl . We argue that this is a plausible estimate of the volume of water locked up in the NAIS at LGM.