The Northeast U.S. continental shelf is a highly productive and economically important region that has undergone substantial changes in recent years. Warming exceeds the global average and several episodes of anomalously warm, sustained temperatures, so called marine heatwaves, have had profound impacts on regional fisheries. A majority of recent research focused on the analysis of temperature, however salinity can serve as a valuable tracer as well. With now more than a decade of remote-sensing sea surface salinity data, we shed new light onto salinity variability in the region with focus on the Mid-Atlantic Bight and assess its role for modulating stratification on the shelf using historic hydrographic data. Seasonal freshwater input via local river discharge drives decreasing salinities in spring and summer on the shelf, but also in the Slope Sea. In spring, freshwater aids the build up of stratification and a freshwater lens of about 20m thickness extends to the shelf break above the pycnocline by the beginning of summer. An observed strong salinification in the fall is linked to offshore forcing over the slope associated with the presence of Warm Core Rings. Coherent low-frequency salinity variability is found over the slope and shelf, highlighting that shelf conditions are significantly impacted by local offshore variability and vice versa. 2015 was characterized by anomalously high salinities, associated with a northerly position of the Gulf Stream. A freshening between 2015 and 2021, is in agreement with increased river discharge. Overall, salinity serves as a valuable additional tracer of these multi-variate processes.
