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Shoreward intrusions of anomalously salty water along the continental shelf of the Middle Atlantic Bight are often observed in spring and summer. Exchange of heat, nutrients, and carbon across the salinity-intrusion front has a significant impact on the marine ecosystem and fisheries. In this article, we developed a method of using an autonomous underwater vehicle (AUV) to detect a salinity-intrusion front and track the front’s movement. Autonomous front detection is based on the different vertical structures of salinity in the two distinct water types: the vertical difference of salinity is large in the intruding saltier water because of the salinity “tongue” at mid-depth, but is small in the nearshore fresher water due to absence of the salinity anomaly. Every time the AUV crosses and detects the front, the vehicle makes a turn at an oblique angle to cross the front, thus zigzagging through the front to map the frontal zone. The AUV’s zigzags sweep back and forth to track the front as it moves over time. From June 25 to 30, 2021, a Tethys-class long-range AUV mapped and tracked a salinity-intrusion front on the southern New England shelf. The frontal tracking revealed the salinity intrusion’s 3-D structure and temporal evolution with unprecedented detail. 

Abstract Monthly observations are used to study the relationship between the Atlantic meridional overturning circulation (AMOC) at 26° N and sea level (ζ) on the New England coast (northeastern United States) over nonseasonal timescales during 2004–2017. Variability inζis anticorrelated with AMOC on intraseasonal and interannual timescales. This anticorrelation reflects the stronger underlying antiphase relationship between ageostrophic Ekman‐related AMOC transports due to local zonal winds across 26° N andζchanges arising from local wind and pressure forcing along the coast. These distinct local atmospheric variations across 26° N and along coastal New England are temporally correlated with one another on account of large‐scale atmospheric teleconnection patterns. Geostrophic AMOC contributions from the Gulf Stream through the Florida Straits and upper‐mid‐ocean transport across the basin are together uncorrelated withζ. This interpretation contrasts with past studies that understoodζand AMOC as being in geostrophic balance with one another.