Using colored dissolved organic matter fluorescence to trace Pacific-derived water in the Eastern Canadian Arctic.

Low-salinity Pacific Water (PW) entering the Arctic Ocean through the Bering Strait is the second largest source of freshwater to the Arctic Ocean and dominates the freshwater inventory of Baffin Bay due to PW advection through Nares Strait and the Canadian Arctic Archipelago (CAA). PW carries nutrients vital for Arctic primary production and the marine ecosystem. Yet, the relative contribution of these pathways to PW advection remains unclear. Here, we focus on PW transport through the northernmost oceanographic passageway of the CAA, Nansen and Eureka Sounds, where observations have been particularly sparse. Using profiles of temperature, salinity and fluorescence of colored dissolved organic matter (FCDOM) collected during the summer of 2024 we contrast PW outflow through Nansen and Eureka Sounds against outflow through Nares Strait and northern Baffin Bay. We find that the subsurface FCDOM maximum successfully traces the PW flow through the CAA and Nares Strait. However, the FCDOM peak of PW erodes when PW passes over the rough bottom topography of the CAA channels and Nares Strait. Further downstream, when PW reaches Jones Sound, Smith Sound, and northern Baffin Bay, lateral interactions with water masses from the West Greenland current and vertical mixing both disrupt the subsurface FCDOM maximum of PW. Overall, our findings indicate that FCDOM assessed by optical sensors is a powerful tool for tracing PW in the CAA, Nares Strait and the adjoining Canada Basin providing valuable insights into water mass mixing processes over the CAA continental shelf and downstream in northern Baffin Bay.