HUDSON STRAIT HEINRICH EVENTS 6 TO 4 REFUTE AN OPEN HUDSON BAY DURING MIS3

Recent papers have argued that Hudson Bay was ice-free during MIS3, specifically between 55 and 35ka BP coinciding with the presence throughout the Labrador Sea of Hudson Strait Heinrich (HS H) layers6,5, 5a, and 4 that span the interval ~60 to 38 ka BP. Thus the issue is whether the marine records refutes an “open MIS3 Hudson Bay” during MIS3. The last advance of the ice sheet along Hudson Strait transported shells on to Nottingham Island and the SE Baffin coast that have dates ≥40 ka and amino acid D/L ratios on the transported shells define the Loks Land interstadial also with an age of >40 ka. CSS Hudsonconducted high resolution seismic surveys that detected the presence of pre-MIS2 sediments in Hudson Strait. Numerous radiocarbon dates on foraminifera and molluscs indicated that deglaciation of outer Hudson Strait was underway by 14 ka and deglaciation took ~5-6 kyr, interrupted by two significant re-advances of Labrador ice. In order to identify the role of Hudson Strait in Labrador Sea H events, the mineral signatures of sediments from Resolution, Eastern, and Western basins and the Ungava Platform (n = 81) were determined by X-ray diffraction---the Ungava Platform composition was notably different. These samples we used as “sources” in a sediment unmixing program using 9 non-clay and 4 clay minerals and compared to the mineral compositions of three cores from the Labrador Sea---HU97048-007, HU2008029-004 and HU2011031-059, 194 km NE, 305 km E, and 1890 km SE respectively from outer Hudson Strait. In these cores, H4 dated at ~38 ka BP, is closely associated with Resolution Basin mineralogy requiring prior major ice sheet and ice stream build-up. In core 059 on the Flemish Cap the mineralogy of H layers 6, 5a, 5, and 4 closely match those from Resolution Basin, and the intra-H6-4 dolomite wt% are >5% indicating continuous glacial erosion. At 059 and nearby sites MD95-2024 and -2026, light d¹⁸O values on planktonic foraminifera matched the detrital carbonate peaks during HS H 6, 5 and 4 indicating the coeval release of glacial meltwater and detrital carbonate-rich sediments. The widespread occurrence of HS H events 6, 5, 5a, and 4 in the Labrador Sea necessitates an ice stream in Hudson Strait and the intervals between them (~7 kyr) are too short to accommodate deglaciation of Hudson Bay and regrowth of the ice sheet.