GSA Connects 2021 in Portland, Oregon

Paper No. 193-5
Presentation Time: 2:30 PM-6:30 PM


BRECKENRIDGE, Andy, Department of Natural Sciences, University of Wisconsin - Superior, Belknap and Catlin, P.O. Box 2000, Superior, WI 54880, LOWELL, Thomas V., Department of Geology, University of Cincinnati, 500 Geology/Physics Building, Cincinnati, OH 45221, WATTRUS, Nigel, Large Lakes Observatory & Department of Earth and Environmental Sciences, University of Minnesota Duluth, 1114 Kirby Drive, HH229, Duluth, MN 55812, PETEET, Dorothy M., Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 and RITTENOUR, Tammy M., Department of Geosciences, Luminescence Laboratory, Utah State University, 4505 Old Main Hill, Logan, UT 84322

Pro-glacial varves from large lakes rimming the Laurentide Ice Sheet (LIS) have the ability to not only resolve LIS sensitivity to late-glacial climate fluctuations, but also reconstruct lake levels and meltwater paleohydrology. Here we provide a varve chronology from glacial lakes Norwood and Agassiz, which fronted the Rainy Lobe of the LIS. The chronology is compiled from sediment cored from 19 modern lakes, which preserve underlying glacial lake sediment, plus correlations to regional varve thickness records in Ontario by Rittenhouse (1933) and Antevs (1951). Radiocarbon and optically-stimulated luminescence results provide direct dates, and an independent check on the varve counts. In total, the varve chronology spans from 14,300 to 10,850 cal. yr BP. We illustrate the utility of the record by: 1) reconstructing century-scale, ice-margin isochrons, 2) comparing ice-margin behavior to Greenland ice-core climate archives, and 3) connecting changes in varve sedimentology to a major drop in Lake Agassiz level known as the Moorhead lowstand. Results indicate that the Moorhead lowstand did not occur until long after the onset of the Younger Dryas, therefore models that link this major Lake Agassiz drawdown to meltwater drainage impacting ocean circulation and global climate should be abandoned.