Hudson Bay was not deglaciated during MIS-3

Abstract

The debate over the dimensions of the Laurentide Ice Sheet during the Middle Wisconsinan has been reinvigorated recently by a claim that Hudson Bay was deglaciated sometime between 57 and 29 ka, based on 735 published dates purported to support a dramatic reduction of the ice sheet. We review the evidence and conclude that an ice-free Hudson Bay in the proposed time window is inconsistent with major plumes of sediment-laden icebergs and meltwater (i.e. Heinrich events) derived from a Hudson Strait ice stream that deposited clastic layers on the sea floor from NE North America to the coast of Europe. We also show that almost all of the 735 published dates are either irrelevant to the claim of an ice-free Hudson Bay, or are mis-interpreted. A careful evaluation of the ∼40 14C ages on Hudson Bay Lowland wood, the most reliable medium for 14C dating sites >∼35 ka, suggests that only two of these dates can be plausibly considered to be finite ages, while the rest of those 14C ages can only be taken at best as minimum limiting ages. Collectively, the sum of the stratigraphic and geochronologic data from the Hudson Bay Lowlands indicate that Hudson Bay was likely deglaciated during Marine Isotope Stage 5a, consistent with Late Quaternary sea-level records, high Northern Hemisphere summer insolation and relatively high atmospheric CO2. But coupled with the nature of Heinrich events we conclude that Hudson Bay remained under a thick Laurentide Ice Sheet throughout MIS-3.