| Summary: | The Northeast U.S. continental shelf is a highly productive and economically important region that has experienced robust changes in upper-ocean properties in recent decades. Warming rates exceed the global and North Atlantic average and in particular several episodes of anomalously warm temperatures, so called marine heatwaves, had devastating impacts on regional fisheries over the past decade. Stratification will strongly impact the magnitude of surface warming. Ocean salinity can play an important role in the development of seasonal stratification, ultimately also modulating horizontal density gradients. Here, we use various available products of sea surface salinity to assess seasonal to interannual variability with focus on the continental shelf south of New England. In-situ data from local observing systems and campaigns provide valuable (sub-) surface data for validation and assessment of the relative roles of temperature and salinity in driving density variability and stratification. Coastal river discharge coast drives a seasonal freshening on the shelf, while shelf break exchange driven by the interaction with Gulf Stream warm core rings is associated with an onshore salt flux. Large-scale forcing in the North Atlantic can impact the along-shelf advection of Arctic-sourced freshwater, which likely shifted the hydrographic properties on the shelf in the recent decade. Salinity serves as an valuable tracer of these multi-variate processes. With now more than a decade of satellite surface salinity we aim to shed new light on the spatiotemporal variability across various scales on the Northeast U.S. continental shelf and how it is embedded in large-scale North Atlantic variability.
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