Increasing Frequency of Mid‐Depth Salinity Maximum Intrusions in the Middle Atlantic Bight.

Shelfbreak exchange processes have been studied extensively in the Middle Atlantic Bight. An important process occurring during stratified conditions is the Salinity Maximum Intrusion. These features are commonly observed at the depth of the seasonal pycnocline, and less frequently at the surface and bottom. Data collected from NOAA's National Marine Fisheries Service Ecosystem Monitoring program as well as data collected from the fishing industry in Rhode Island show that the middepth intrusions are now occurring much more frequently than was reported in a previous climatology of the intrusions (Lentz, 2003, https://doi.org/10.1029/2003JC001859). The intrusions have a greater salinity difference from ambient water and penetrate large distances shoreward of the shelf break relative to the earlier climatology. The longer term data from the Ecosystem Monitoring program indicates that the increase in frequency occurred in 2000, and thus may be linked to a recent regime shift in the annual formation rate of Warm Core Rings by the Gulf Stream. Given the increased frequency of these salty intrusions, it will be necessary to properly resolve this process in numerical simulations in order to account for salt budgets for the continental shelf and slope. Plain Language Summary: An important exchange process between waters of the continental slope and continental shelf is the Salinity Maximum Intrusion. These have been studied before but there is little information on their along‐shelf scale, how they are generated, or their broad impact on shelf ecosystems. Observations from both a multi‐decadal data set from the National Marine Fisheries Service as well as community science data collected by the commercial fishing industry over 5 years show that the frequency of these intrusions has increased significantly since 1998. In addition, the intrusions appear to be saltier and penetrate further onshore than previous reports. Future work is necessary to determine how the increasing frequencies of this important process may be affecting continental shelf heat and salt balances as well as broader impacts to the continental shelf ecosystem. Key Points: Observations over several decades show substantial increase of frequency of middepth Salinity Maximum IntrusionsThere is significant inter‐annual and month‐to‐month variability in the frequency and occurrence of Salinity Maximum IntrusionsSalinity Maximum Intrusions now commonly extend up to 100 km shoreward of the shelfbreak and profiles may contain multiple intrusions [ABSTRACT FROM AUTHOR]