Middle Wisconsinan marine shells near Repulse Bay, Nunavut, Canada: implications for Marine Isotope Stage 3 ice‐free conditions and Laurentide Ice Sheet dynamics in north‐west Hudson Bay

Abstract

Evidence suggesting a reduction of the Laurentide Ice Sheet (LIS) during Marine Isotope Stage 3 (MIS 3) is widespread but the boundaries of the ice sheet and the timing of minimum ice extent are still poorly constrained. Radiocarbon dating of glacially transported marine mollusks in Rae Isthmus ice stream till south of Repulse Bay, Nunavut, Canada, provides new evidence for MIS 3 deglaciation in the north‐west part of Hudson Bay. Middle Wisconsinan finite 14C ages varying between 31.7 and 39.2k 14C a BP (∼35.0 and 43.7k cal a) indicate a marine event(s) for a minimum of ∼8.7k cal years. Our findings suggest ice‐free conditions in the ice stream source area in proto‐Roes Welcome Sound, and therefore significant glacial recession of the LIS margin during the Middle Wisconsinan, much farther in the interior of the ice sheet than previously known. The marine incursion possibly occurred because of a calving bay developed from the north in the Gulf of Boothia − Committee Bay area following the recession and collapse of the ice stream. After the MIS 3 marine episode(s), the topographically controlled ice stream stemming from the eastern end of the Keewatin Ice Divide was re‐activated, and maintained until deglaciation.

A new global ice sheet reconstruction for the past 80 000 years

“…1 a–c), we have set the timing of the retreat of ice from Hudson Bay in MIS 3 to coincide with Heinrich Event 5 (45,000 yr BP), with ice-free conditions only lasting a few thousand years, before becoming ice covered again by 40,000 yr BP. This timing makes it possible to explain the finite-aged radiocarbon dates found in both northern and southern Hudson Bay 5 – 7 . After this event, there was a gradual expansion of the ice sheet to the culmination of the LGM.…”

“…Recent work in the Hudson Bay region in North America 5 – 7 shows that during part of MIS 3, ice-free conditions may have existed. Under this interpretation, the climatic conditions in this area were favorable to allow the growth of forests, with a climate that was potentially analogous to present 8 .…”

The marine δ18O record overestimates continental ice volume during Marine Isotope Stage 3

“…Additional evidence for ice-free conditions near the geographic center of the Laurentide Ice Sheet comes from radiocarbon dating of glacially transported marine mollusks in northwest J o u r n a l P r e -p r o o f Hudson Bay near Repulse Bay (Rae Isthmus ice stream; McMartin et al, 2019). In that area, eight shell samples from five sites yielded finite radiocarbon ages ranging from 35.8 ± 0.5 ka to 42.4 ± 0.5 ka (calibrated using Calib 8.1.0 and Marine 20 with 1σ error; Heaton et al, 2020;Reimer et al, 2020;Stuiver and Reimer, 1993).…”

“…Dredge and Thorleifson, 1987;Dyke et al, 2002). However, recent stratigraphic studies have reported new geochronological and biostratigraphic data from the core of glaciated regions that argue for significant changes in Northern Hemisphere ice extent during MIS 3 (Dalton et al, 2016;Helmens, 2014;McMartin et al, 2019;Sarala et al, 2016;. Furthermore, recent glacial isostatic adjustment modelling efforts support the feasibility of reduced ice cover and volume in some key areas of the formerly glaciated region (Gowan et al, 2021;Pico et al, 2018;Pico et al, 2017).…”

Was there a glacial outburst flood in the Torngat Mountains during Marine Isotope Stage 3?

“…Although documenting the growth of the Laurentide Ice Sheet is challenged by the sparsity of preserved records, recent work has refined Laurentide Ice Sheet extent and volume during MIS 3. In particular, there is an increasing number of nonglacial deposits in the Hudson Bay lowlands (Dalton et al, 2016), St. Lawrence lowlands (Parent et al, 2015), Repulse Bay (Mcmartin et al, 2019), New England (Munroe et al, 2016), and Atlantic Canada (Remillard et al, 2017), dated between 60 and 35 ka (Figure 2). This evidence suggests a substantially reduced ice sheet at ~50-35 ka relative to the LGM, with ice possibly restricted to two separate domes over eastern and western Canada at that time (Dalton et al, 2019).…”