Abstract

A time-dependent, flow-line ice-sheet model is used to explore interactions between last glacial climate, the Laurentide ice sheet, and the Great Lakes. We seek to understand perturbations in the ice-flow field that caused three neighboring lobes to leave different geomorphic and sedimentary records. Driven by reconstructed air- temperature variations from 65 to 18 ka, the simulated lobe dynamics are consistent with constraints from loess and till chronologies, till stratigraphy, and ice-surface profiles. Contrasts in lobe dynamics are best explained by the geometry of lakes along each flow line. As ice entered these lakes, calving influenced glacier mass balance. In particular, deep water in Lake Superior likely delayed ice advance into northern Wisconsin by promoting large calving losses, whereas lobes to the east that encountered shallower water were less affected by calving. The Driftless Area of Wisconsin may thus owe its existence, at least in part, to the presence of Lake Superior. Our results suggest that morainal-bank evolution should be treated in ice-sheet models in lacustrine and shallow-marine settings. Determining the sediment flux to the morainal bank remains a difficult task. For example, ice advance across central Lake Superior was probably sediment-flux limited. Otherwise, the Driftless Area would have been glaciated.

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