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Abstract The Northeast U.S. continental shelf (NEUS) 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 have had profound impacts on regional fisheries. A majority of recent research studies 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 historical hydrographic data. Local river discharge drives decreasing salinities not only in spring and summer on the shelf but also in the Slope Sea. In spring, fresher water aids the build‐up of stratification and a low salinity surface layer extends to the shelf break above the pycnocline by the beginning of summer. An observed 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 offshore variability. Conditions on the NEUS in 2015 were 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 cumulative discharge as well as lower offshore salinities. Overall, salinity serves as a valuable additional tracer of these multi‐variate processes. 

Abstract Despite the ubiquity of eddies at the Mid‐Atlantic Bight shelf‐break front, direct observations of frontal eddies at the shelf‐break front are historically sparse and their biological impact is mostly unknown. This study combines high resolution physical and biological snapshots of two frontal eddies with an idealized 3‐D regional model to investigate eddy formation, kinematics, upwelling patterns, and biological impacts. During May 2019, two eddies were observed in situ at the shelf‐break front. Each eddy showed evidence of nutrient and chlorophyll enhancement despite rotating in opposite directions and having different physical characteristics. Our results suggest that cyclonic eddies form as shelf waters are advected offshore and slope waters are advected shoreward, forming two filaments that spiral inward until sufficient water is entrained. Rising isohalines and upwelled slope water dye tracer within the model suggest that upwelling coincided with eddy formation and persisted for the duration of the eddy. In contrast, anticyclonic eddies form within troughs of the meandering shelf‐break front, with amplified frontal meanders creating recirculating flow. Upwelling of subsurface shelf water occurs in the form of detached cold pool waters during the formation of the anticyclonic eddies. The stability properties of each eddy type were estimated via the Burger number and suggest different ratios of baroclinic versus barotropic contributions to frontal eddy formation. Our observations and model results indicate that both eddy types may persist for more than a month and upwelling in both eddy types may have significant impacts on biological productivity of the shelf break.