Shoreward Migration of the Shelfbreak Front in the Middle Atlantic Bight

The Northwest Atlantic continental shelf is home to one of the richest ecosystems in the world, however it is also among the fastest warming regions globally and experienced multiple temperature extreme events, termed marine heatwaves, in the recent decade. These ongoing changes pose a large challenge for the highly valuable fishing industry in the Northeast U.S.. The generally cooler and fresher shelf water is supplied by subpolar waters via the Labrador current, while offshore waters in the Slope Sea, that is the continental slope region bounded by the Gulf Stream and the shelfbreak, are of subtropical origin. Warm core rings shedding of the Gulf Stream transport warm and saline water but also nutrients shoreward and frequently cause cross-shelf intrusions when interacting with bathymetry. The boundary of the two water masses is the Shelfbreak Front and the foot of the front is climatologically found over the 100\,m isobath in the northern Middle Atlantic Bight. While marking a transition of physical properties, the front and its position has also large implications for fisheries as temperate species are found shoreward of the front and more tropical species remain offshore of the front in the warm, saline waters. Monitoring the frontal position is challenging and requires high-resolution sampling, however large and persistent diversions may be detectable in coarser and more sporadic observations. Using data from the Coastal Pioneer Array by the Ocean Observative Initiative along with recent observations obtained during research cruises on the continental shelf and satellite-based sea surface salinity, we assess indicators of the frontal position in recent years. In 2021 the front migrated tens of km inshore for multiple months resulting in irregularities for the regional fishermen. This migration was likely connected to the presence of multiple warm core rings in the Slope Sea, driving record temperatures over the slope and shelf. We address the question whether similar frontal shifts occur more frequently and discuss how these maybe connected to larger scale forcing such as a shifting Gulf Stream, a slowing Atlantic Meridional Overturning Circulation or changes in the supply of subpolar water to the shelf.