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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.
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Seasonal Salinification of the US Northeast Continental Shelf Cold Pool Driven by Imbalance Between Cross‐Shelf Fluxes and Vertical Mixing
Abstract The US Northeast continental shelf “cold pool” comprises winter‐cooled Shelf Water that is trapped below the warm surface layer during the stratified season. The regional ecosystem relies on the preservation of winter temperatures within the cold pool throughout the year. Here, we present first evidence of a significant increase in the cold pool's salt content on the US Northeast continental shelf throughout the stratified season, suggesting that shelfbreak exchange contributes strongly to the seasonal erosion of the cold pool. Cold pool salinification rates of remain steady throughout the stratified season, leading to salinity differences of over between April and October. A cold‐pool salinity budget reveals that the observed salinification is caused by an imbalance between cross‐shelf salt fluxes, which deposit salt into the cold pool at all times of year, and the strong seasonal cycle of vertical mixing. During the stratified season, vertical mixing is inhibited and no longer counteracts the cross‐shelf flux, leading to net salinification of the cold pool over the summer. Along‐shelf freshwater advection from upstream is only present in the fall and contributes some additional freshening to shut down the salinification trend. Seasonal variability in the position of the US Northeast shelfbreak front is too small and out of phase to contribute to the salinity increase. The strong relationship between the seasonal cycle of cold pool modification and seasonal stratification points toward the importance of the timing of spring re‐ and fall de‐stratification on near‐bottom continental shelf temperature and salinity.
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- Award ID(s):
- 2241407
- PAR ID:
- 10665397
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 130
- Issue:
- 5
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2024JC021270
