Surface winds across eastern and midcontinental North America during the Last Glacial Maximum: A new data-model assessment

Abstract

Last Glacial Maximum (LGM) proxy evidence of surface wind direction across eastern and midcontinental North America comes primarily from loess and dune deposits, and overwhelmingly suggests surface winds had a strong westerly component. However, the season of sediment deposition and the temporal scale of wind information preserved in these deposits remains uncertain. Furthermore, paleoclimate model simulations over the last several decades have indicated a predominance of easterly winds across this region, due to the presence of an anticyclone over the Laurentide Ice Sheet as well as katabatic winds flowing off the ice sheet and over the adjacent land surface. Here we reassess model-data near-surface wind direction agreement using nine general circulation models participating in the LGM experiment of the third Paleoclimate Model Intercomparison Project (PMIP3) and a compilation of previously published paleowind directions from loess and dune deposits dating to the LGM. We find the highest overall model-proxy data agreement in winter (December–February), indicating predominantly westerly winds across the region in the LGM model simulations. We also find high zonal and meridional wind direction agreement in spring (March–May) and fall (September–November) in many models. Winter, spring and fall also have faster mean daily near-surface wind speeds in the LGM simulations relative to pre-industrial control simulations. Thus, this model-data assessment suggests LGM aeolian deposition in the study region likely occurred dominantly in these three seasons, at times when local conditions favorable for aeolian deflation coincided with high wind speed events. Models that agree best with the proxy data have strengthened Aleutian and Icelandic Low pressure systems and a weakened Laurentide High pressure system, which constrains the spatial footprint of the Laurentide High to the ice sheet, reducing northeasterly winds near the ice sheet margin. A weaker Laurentide High in turn coincides with warmer surface temperatures over the ice sheet and the North Atlantic. The strength and location of semi-permanent pressure systems were thus key controls on surface wind direction across midcontinental and eastern North America during the LGM.