Spits Formed in Glacial Lake Algonquin Indicate Strong Easterly Winds Over the Laurentide Great Lakes During Late Pleistocene

Randall J. Schaetzl, Frank J. Krist Jr., Michael D. Luehmann, C.F. Michael Lewis, and Michael J. Michalek

We report on a unique, new dataset: 49 spits that formed in the various phases of Glacial Lake Algonquin in the northern Great Lakes region, between approximately 13,200 and 11,500 years BP. The spits, which are now subaerially exposed well above the level of the current Great Lakes, trail off from former Lake Algonquin islands and headlands. Several exceed 10 km in length. Steep, eroded headlands coupled with their coarse-textured sediments, suggest that spit development was driven by large waves and strong longshore currents. The lake’s islands and exposed headlands are usually strongly eroded on their eastern margins. Additionally, spits within &150–200 km of the former ice margin, and especially the very large spits in northern Michigan, trail to the west, particularly the WNWand SW. Some small spits that lie farther south trail to the east, and others, within confined bays, better reflect the localized littoral circulation systems. Together, these features provide on-the-ground evidence for persistent, easterly, summertime winds in the late Pleistocene in the northern Great Lakes region, supporting paleoclimate models that show southeasterly to easterly air flows, originating from a glacial anticyclone above the Laurentide Ice Sheet. Our research suggests that strong, anticyclonically driven, easterly winds were a key part of the regional circulation within &150–200 km of the southern ice margin, while acknowledging that winds may have been more dominantly westerly at locations farther south. The latter conclusion reconciles with the record of loess transport and dune formation on westerly winds during this (and earlier) time periods in the south-central Great Lakes region and the Great Plains of North America.