An Eastern Gulf of Maine Salinity Index for Monitoring Winter Scotian Shelf Inflow and Its Relation to Coastal and Interior Pathways

The Gulf of Maine (GoM) hosts a variety of fish and sea mammals, beaches, and active commercial fishery. Understanding, monitoring, and predicting the status of and future changes in its food web and water quality are key goals of an ocean observing system that utilizes in situ buoys, gliders, shipboard surveys, satellite remote sensing, and numerical modeling. This study defines and explores the utility of a new Gulf-specific water mass exchange predictor designed to capture changes in winter inflow of fresh and cold waters from the upstream Scotian Shelf using soil moisture active passive satellite sea surface salinity (SSS) in the eastern GoM. A data assimilative ocean circulation model is used to characterize and assess results. GoM food web dynamics and water quality both depend on lower trophic productivity associated with Gulf-wide phytoplankton and zooplankton communities, and these are fundamentally controlled by water temperature and inorganic nutrients that often change due to varied exchange with the adjoining offshore North Atlantic and upstream Nova Scotian Shelf Water (SSW) that flows around southwestern Nova Scotia. Once in the Gulf, most of the SSW inflow to the eastern GoM is advected along southwestern Nova Scotia. This eastern GoM area (termed eGoM) is a useful gauge area where SSS reflects variations in SSW inflow. Results indicate that the SMAP-derived winter eGoM salinity index can help explain interannual variability in GoM conditions during the ensuing spring to summer, the seasons influenced by several advective pathways, as discussed in the study.