Patterns of ice recession and ice stream activity for the MIS 2 Laurentide Ice Sheet in Manitoba, Canada

Abstract

Reconstruction of deglacial ice margins provides insights into the demise of past ice sheets and ice-marginal lakes and helps to understand how former ice sheets responded to climate change. Here, we reconstruct deglacial Laurentide Ice Sheet margins across Manitoba (Canada), a dynamic region that in MIS 2 spanned from an inner core region of the Keewatin dome to the periphery of the ice sheet (~900 km north of the Last Glacial Maximum limit). The area was also overrun by ice flowing from both the Quebec-Labrador dome and the Hudson Bay Ice Saddle. The surficial landscape of Manitoba contains inherited relict and palimpsest glacial landscapes, which need to be separated from deglacial features. Ice-impounded glacial Lake Hind was present in southwest Manitoba at 13.0 cal. ka BP, meaning most of Manitoba was covered by ice at the start of the Younger Dryas. Northwest drainage of glacial Lake Agassiz in front of the Highrock Lake–Cree Lake moraine could have occurred near the end of the Younger Dryas, prior to 11.5 cal. ka BP, though the volume of the lake varies greatly depending on ice-margin reconstructions. Our interpretation is incompatible with the hypothesis that Lake Agassiz drainage to the Arctic Ocean triggered the Younger Dryas climatic cooling. Numerous ice streams developed across central and southern Manitoba during deglaciation, including the Souris, Red River, The Pas, Hayes and Quinn Lake. The dominant ice source was from the north early in deglaciation, switching to the northeast with growth of the Hudson Bay Ice Saddle and then back to the north again with demise of the saddle. The ice-margin ages are largely unconstrained, and thus we are unable to accurately assign climatic drivers to various ice stream events. Nonetheless, we record the development and demise of terrestrial ice streams over both hard-bed and soft-bed substrates.