Seasonal to interannual variability of salinity on the Northeast U.S. continental shelf and links to large-scale North Atlantic variability

<p>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, have had devastating impacts on regional fisheries over the past decade. Stratification will strongly impact the magnitude of surface warming, i.e., a thin surface layer will heat faster, as well as facilitate cross-shelf exchange. 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. Data from the Coastal Pioneer array from the Ocean Observatory Initiative provides an ideal basis for validation and furthermore provides valuable subsurface data that allows assessment of the relative roles of temperature and salinity in driving density variability and stratification. River discharge along the eastern U.S. and Canadian 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. Furthermore, large-scale forcing in the North Atlantic can impact the along-shelf advection of Arctic-sourced freshwater, which likely shifted the shelf to higher salinities (along with warmer temperatures) in the recent decade. Salinity serves as a valuable tracer, in addition to temperature (having a large diurnal and seasonal cycle), of these multi-variate processes. With now more than a decade of satellite surface salinity we aim to shed new light on the spatio-temporal variability across various scales on the Northeast U.S. continental shelf and how it is embedded in large-scale North Atlantic variability.</p>