Late-Pleistocene paleowinds and aeolian sand mobilization in north-central Lower Michigan

Simulation of late glacial atmospheric conditions with atmospheric general circulation models suggest a strong anticyclone over the Laurentide Ice Sheet and associated easterly winds along the glacial margin. In the upper Midwest of North America, evidence supporting this modeled air flow exists in the orientation of paleospits in northeastern Lower Michigan that formed ~13. ka in association with glacial Lake Algonquin. Conversely, parabolic dunes that developed between 15 and 10. ka in central Wisconsin, northwestern Indiana, and northwestern Ohio resulted from westerly winds, suggesting that the wind gradient was indeed tight. Study results refine our understanding of late-Pleistocene wind conditions even closer to the ice margin in the upper Midwest by focusing on the timing of aeolian sand mobilization in north-central Lower Michigan at the Rosco dune field. The area was deglaciated ~16. ka, and parabolic dunes have westerly orientations, indicating that they resulted from westerly winds. Optical ages suggest that mobilization last occurred between about 13. ka and 10. ka. The close proximity (~150. km) of this dune field to more northerly paleolacustrine landforms resulting from easterly winds suggests that anticyclonic circulation indeed extended only a very short distance south of the ice sheet, which is consistent with modeled airflow and the orientation of dunes in central Canada. This study also presents evidence suggesting that, in addition to prevailing winds, dunes likely formed because the sparsely-vegetated local outwash plain was deflated.