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Mapping of a Mid‐Depth Salinity Maximum Intrusion South of New England in June 2021 and Implications for Cross‐Shelf Exchange.

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Title: Mapping of a Mid‐Depth Salinity Maximum Intrusion South of New England in June 2021 and Implications for Cross‐Shelf Exchange.
Authors: Gawarkiewicz, Glen G.1 (AUTHOR) ggawarkiewicz@whoi.edu, Taenzer, Lukas L.1,2 (AUTHOR), Silver, Adrienne1 (AUTHOR), Ryan, Svenja1 (AUTHOR), Green, Erica3 (AUTHOR), Gangopadhyay, Avijit4 (AUTHOR), Musgrave, Ruth5 (AUTHOR), Bahr, Frank1 (AUTHOR), Kukulya, Amy6 (AUTHOR), Yoder, Noa7 (AUTHOR)
Source: Journal of Geophysical Research. Oceans. Jun2025, Vol. 130 Issue 6, p1-16. 16p.
Subject Terms: Fish larvae, Hydrographic surveying, Gulf Stream, Autonomous underwater vehicles, Continental shelf
Abstract: The Northeast U.S. continental shelf is characterized by relatively cold and fresh shelf waters of Arctic origin, whereas the adjacent Slope Sea is home to warm and salty, Gulf Stream derived waters. These contrasting watermass properties form a strong Shelfbreak Front, which can act as dynamical barrier of exchange between onshore and offshore waters. A shelfbreak exchange process which has been commonly observed in the Middle Atlantic Bight, south of New England, is the mid‐depth salinity maximum intrusion, occurring predominantly in the stratified season. It is easily identified within salinity profiles, and yet there have been few hydrographic surveys that have resolved the spatial extent of these features. In order to study these features in more detail, a dedicated research cruise was directed in June 2021 toward mapping and characterization of one of these intrusions. Using a combination of shipboard CTD profiles, Autonomous Underwater Vehicle missions, and a towed microstructure profiler, a strong intrusion was mapped in three‐dimensions for the first time. The intrusion penetrated 33 km onshore of the upper portion of the Shelfbreak Front, was 14 km wide in the along‐shelf, and was 10–30 m thick. A warm core ring was directly offshore of the intrusion and likely contributed to the initiation of the intrusion. The intrusion contributed about 2.5% additional salt relative to the ambient salinity structure. These intrusions are relevant for the shelf salinity budget as well as the onshore transport of larval fish and are thus an important process for the shelf ecosystem. Plain Language Summary: An important cross‐shelf exchange mechanism that has been observed for nearly a hundred years in profiles of salinity has recently been shown to be increasing in frequency. It is potentially a significant process for the onshore transport of larval fish, such as eels, and squid. Despite frequent observations, the spatial scales of these intrusions have not been clearly identified in the past. A dedicated research cruise in June 2021 was able to map one of these intrusions and show that it was particularly salty, likely because of the close proximity of a Gulf Stream warm core ring. The intrusion penetrated a substantial distance onshore, and carried the equivalent of 2.5% of the total salt in the surrounding water onshore. This process may be significant in determining how larval fish move onshore to estuaries and how squid move onshore and are available for commercial harvesting. Key Points: A mid‐depth salinity maximum intrusion has been successfully mapped for the first time south of New EnglandThe intrusion had a large salinity contrast with the ambient shelf water massThe intrusion was in close proximity to a warm core ring immediately offshore, which likely contributed to the formation of the intrusion [ABSTRACT FROM AUTHOR]
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Abstract:The Northeast U.S. continental shelf is characterized by relatively cold and fresh shelf waters of Arctic origin, whereas the adjacent Slope Sea is home to warm and salty, Gulf Stream derived waters. These contrasting watermass properties form a strong Shelfbreak Front, which can act as dynamical barrier of exchange between onshore and offshore waters. A shelfbreak exchange process which has been commonly observed in the Middle Atlantic Bight, south of New England, is the mid‐depth salinity maximum intrusion, occurring predominantly in the stratified season. It is easily identified within salinity profiles, and yet there have been few hydrographic surveys that have resolved the spatial extent of these features. In order to study these features in more detail, a dedicated research cruise was directed in June 2021 toward mapping and characterization of one of these intrusions. Using a combination of shipboard CTD profiles, Autonomous Underwater Vehicle missions, and a towed microstructure profiler, a strong intrusion was mapped in three‐dimensions for the first time. The intrusion penetrated 33 km onshore of the upper portion of the Shelfbreak Front, was 14 km wide in the along‐shelf, and was 10–30 m thick. A warm core ring was directly offshore of the intrusion and likely contributed to the initiation of the intrusion. The intrusion contributed about 2.5% additional salt relative to the ambient salinity structure. These intrusions are relevant for the shelf salinity budget as well as the onshore transport of larval fish and are thus an important process for the shelf ecosystem. Plain Language Summary: An important cross‐shelf exchange mechanism that has been observed for nearly a hundred years in profiles of salinity has recently been shown to be increasing in frequency. It is potentially a significant process for the onshore transport of larval fish, such as eels, and squid. Despite frequent observations, the spatial scales of these intrusions have not been clearly identified in the past. A dedicated research cruise in June 2021 was able to map one of these intrusions and show that it was particularly salty, likely because of the close proximity of a Gulf Stream warm core ring. The intrusion penetrated a substantial distance onshore, and carried the equivalent of 2.5% of the total salt in the surrounding water onshore. This process may be significant in determining how larval fish move onshore to estuaries and how squid move onshore and are available for commercial harvesting. Key Points: A mid‐depth salinity maximum intrusion has been successfully mapped for the first time south of New EnglandThe intrusion had a large salinity contrast with the ambient shelf water massThe intrusion was in close proximity to a warm core ring immediately offshore, which likely contributed to the formation of the intrusion [ABSTRACT FROM AUTHOR]
ISSN:21699275
DOI:10.1029/2024JC021536