Biological characterization of a mid‐water salinity maximum intrusion over the Northeast US Shelf

Le résumé fourni par la source

Abstract Salinity maximum intrusions, subsurface layers of anomalously salty and warm continental slope water moving onto the continental shelf along the thermocline, are recurring features over the Northeast US Shelf and represent an important cross‐shelf exchange mechanism. While their physical characteristics have been described, the biological composition and ecological role of these intrusions remain poorly understood. Here, we combine multidisciplinary physical, biological, and biogeochemical observations from summer 2023 to provide direct evidence that salinity maximum intrusions advect offshore biological communities onto the continental shelf, focusing on an event that ranked among the strongest recorded in terms of salinity anomaly and spatial extent. The intrusion layer coincided with distinct acoustic scattering layers containing amphipods and larvae of shrimp, crab, and fish. Several offshore phytoplankton taxa of different cell sizes including Prochlorococcus , Trichodesmium colonies, and mixotrophic dinoflagellates were also observed, with rhizarians the only small zooplankton consistently present within the intrusion layer. The presence of flatfish and crustacean larvae highlights the role of intrusions in early life‐history connectivity, while amphipod aggregations—likely linked to elevated food supply and reproductive demand—suggest that intrusions can also act as feeding hotspots. With their increasing frequency and shoreward extent, salinity maximum intrusions emerge as a dynamic mechanism shaping community composition and mediating cross‐shelf biological connectivity on the Northeast US Shelf.

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