Abstract

A survey of the chronology of late Pleistocene glaciers in the western United States indicates a record of glacier advances during the last glaciation which is more variable than that predicted by orbital forcing. Numerical dating of late Pleistocene deposits from the Puget lobe of the Cordilleran ice sheet and alpine glaciers and ice caps in the Rocky Mountains and Cascade Range suggests that advances and retreats of these glaciers were in phase with episodes of growth and collapse of the Laurentide ice sheet associated with the North Atlantic Heinrich events. Specifically, the existing chronologies indicate that these glaciers were advancing to their terminal areas up to several thousand years before a Heinrich event and retreated shortly thereafter. Because midlatitude glaciers respond relatively rapidly to climate change, this complex record of glacial fluctuations suggests mechanisms of climate forcing in western North America that are in some way tied to Heinrich events. One possible mechanism involves southerly and northerly displacement of the jet stream across the western United States in response to growth and collapse of the Laurentide ice sheet.

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