FORAMINIFERAL STRATIGRAPHY AND LITHOFACIES REVEAL THE TIMING AND ENVIRONMENTS OF DEGLACIATION AND ONSET OF ARCTIC/ATLANTIC THROUGHFLOW IN THE ARCTIC ISLAND CHANNELS

The Arctic Island Channels (AIC) usher low-salinity, nutrient-rich Arctic surface water (ASW) and sea ice into the North Atlantic with consequences for the Atlantic Meridional Overturning Circulation (AMOC). The channels were blocked to Arctic/Atlantic throughflow by confluent ice sheets until the early Holocene. However, the timing of opening of the channels is poorly constrained as is the ensuing development of the North Water polynya that occupies northern Baffin Bay today, with productivity fueled by nutrient rich ASW. Sediment cores from key sites near the mouths of these channels capture sediment sequences that reflect environments of ice-sheet retreat through to the development of modern conditions in northern Baffin Bay. Foraminiferal assemblage data from these cores provide insight into the environmental conditions during deglaciation and establishment of the Arctic/Atlantic throughflow and also provide ¹⁴C dates to constrain the timing of events. A pair of ¹⁴C dates on benthic and planktic foraminifers from the same sample suggests that the local reservoir correction, ΔR= 600 years, can be applied to early Holocene dates on benthic organisms in the deep shelf trough sites of our cores (>580 m) in this area. In Lancaster Sound cores, glaciomarine conditions as defined by pebbly mud lithofacies overlying till begin by 11.1 cal ka BP and end at about 10.5 cal ka BP based on lack of >2mm clasts interpreted as ice rafted detritus (IRD). The overlying mud unit with pyritized burrows and highly abundant calcareous benthic and planktic foraminifers as well as an increase in biogenic silica suggests that Lancaster Sound may have been open to the Arctic Ocean by 10.5 cal ka BP. An agglutinated faunal zone with >80% agglutinated foraminifers coincides with a change to increased bioturbation and lower sedimentation rates. This zone begins soon after 8.7 cal ka BP based on ¹⁴C dates on seaweed macrofossils in 3 cores and is similar in timing to the opening of Nares Strait to ASW throughflow. A later increase in biogenic silica c. 5.8 cal ka BP in cores farther east off Smith Sound may reflect the formation of the North Water polynya.