REVIEWING GEOLOGICAL AND NUMERICAL EVIDENCE ON THE EXTENT OF THE LAURENTIDE ICE SHEET DURING MARINE ISOTOPE STAGE 3 (Invited Presentation)

The evolution of the North American ice sheet complex (consisting of the Laurentide, Innuitian and Cordilleran ice sheets) prior to the last glacial maximum (~25 ka) has been the subject of intense research because this interval offers a critical long-term perspective from which to study the response of continental ice sheets to climatic change. Here, we review a suite of geological and numerical evidence that constrain the extent of the Laurentide Ice Sheet (LIS), the largest North American ice sheet, during Marine Isotope Stage 3 (MIS 3; ~57 ka to ~29 ka). We discuss hemispheric-scale inferences from the δ¹⁸O and atmospheric records, along with more local evidence from the chronostratigraphic record in the glaciated and unglaciated regions. We also discuss recent modelling efforts to ascertain ice sheet dynamics and sea level during this interval. Overall, there is conflicting evidence for the extent of the LIS during MIS 3: some studies provide evidence of a large ice sheet; others argue for severely reduced ice over central Canada, and other studies support a highly dynamic configuration of the ice sheet. Our goal is to facilitate a discussion on the key pieces of evidence and develop pathways for future collaborative research on this critical time interval. Key areas for future research include the development of additional proxies to track the ice extent and improved geochronological dating methods on stratigraphic records in the glaciated regions, as well as additional study of the causes and mechanisms behind Henrich Events.