Signatures and pathways of subsurface Gulf Stream water intrusions and fresh water lenses on the shelf to the north of Cape Hatteras

In May/June of 2017, an extensive campaign of glider and ship-based measurements were made to observe submesoscale features on the North Carolina shelf north of Cape Hatteras. This effort was part of a collaboration between the U.S. Naval Research Laboratory’s (NRL) “Smart Glider Teams for Rapid Update of Local Analysis” project and the National Science Foundation funded multi-institution project titled, “Processes Driving Exchange at Cape Hatteras” (PEACH). Altogether, six NRL gliders collected more than 13,000 CTD profiles, which were supplemented by 144 ship-collected CTDs and 7 Underway-CTD sections. The warmest and saltiest waters (> 22°C and > 35.5 psu) that were observed on the shelf during this period often occurred as sub-surface intrusions north of 35.6°N and as shelf-bottom waters south of 35.6°N closer to Cape Hatteras. Typical depth ranges for the intrusions centered at 10-40 m below the sea surface, with thickness of a few meters to greater than 10 meters. Additionally, very fresh (< 30.5 psu) surface lenses were observed both near the shore and near the shelf-break by the gliders and by the ship’s thermosalinograph that suggest a fresh water circulation pattern which traces the edges of a mesoscale eddy on the shelf. The pathways of the Gulf Stream intrusions and the fresh water lenses are being analyzed using these data sets and data-assimilative runs of high-resolution Navy Coastal Ocean Model simulations of the shelf near Cape Hatteras.