Timing and Paleoceanographic Impacts of the Onset of Arctic-Baffin Bay Throughflow
Changes in the amount of sea ice and low salinity surface water (together called freshwater) that flow from the Arctic Ocean to the North Atlantic have global ocean circulation and climate impacts. The research involves analysis of the timing and consequences of the opening of the western route for Arctic freshwater flux after the retreat of glacier ice at the end of the last glaciation. The Arctic freshwater flows through the western route to the Labrador Sea, which is a critical area of deep ocean convection. Diverse analyses of sediment cores from northern Baffin Bay and computer modeling will be used to document and explore the large changes in sea-ice cover, Arctic freshwater flux, ocean circulation, marine productivity, and ocean acidification over the last 11,000 years that are associated with opening of the western freshwater route. An important component of the research is to study the history of the North Water Polynya (NOW), an oasis of high productivity and low sea-ice cover that forms where the Arctic freshwater enters northern Baffin Bay. The productivity of the NOW owes to the high nutrient content of the Arctic freshwater and to the blockage of Arctic sea-ice floes by the constricted channels forming the gateway. The NOW is a hotspot of biological productivity that has attracted humans to the area for millennia and sustains Arctic communities today. Both the history of freshwater flux via the western freshwater route and the history of the NOW are very poorly known, yet the behavior of this system is poised to change in response to continuing reductions in Arctic sea-ice cover. The understanding of how the opening of the western route of Arctic freshwater and the initiation of the NOW have changed through time will provide context to understand how these systems will affect the Arctic systems and global climate in future. The project uses existing sediment cores from the NOW polynya, and areas upstream of and downstream from it using both novel (nutrient tracers from Inductively Coupled Plasma Mass Spectrometry and algal biomarkers) and traditional (quantitative X-ray mineralogy, foraminiferal assemblages, stable C and O isotopes) proxies, climate modeling with the Community Earth System Model (CESM) and Glacial Isostatic Adjustment modeling and chronology development (radiocarbon and paleomagnetic secular variation) to test three hypotheses: Hypothesis 1: The opening of the western freshwater route of the Arctic-Atlantic throughflow changed the freshwater outflow to the North Atlantic with consequences for the Atlantic Meridional Overturning Circulation (AMOC). Hypothesis 2: Significant shallowing of the CAA channels by glacial isostatic uplift has changed the composition of the Arctic outflow with consequences for carbonate preservation and the AMOC. Hypothesis 3: The NOW formed in the middle to late Holocene as a consequence of increased Arctic sea-ice. The project is an international effort involving Canadian and EU cooperation and foreign graduate student interaction with CU faculty and scientists. It will provide support and mentoring for a female post-doc who will receive training in novel biogeochemical laboratory techniques. A PhD student will work on the CESM modeling. Several undergraduate students will receive training and participate in the research.