Boundaries between subtropical and subpolar oceanic gyres are characterized by confluent western boundary currents in the open ocean, like the Gulf Stream/Slope Sea confluence at Cape Hatteras. These regions also feature convergence in the adjacent shelf and slope waters, which leads to large net export of shelf waters to the open ocean. Complex, bidirectional shelf-open ocean exchange also occurs and is driven by variability in the western boundary currents, atmospheric forcing, and shelf water properties, and is influenced by local bathymetric characteristics. Exchanges between the shelf and open ocean are central to global carbon budgets, marine ecosystem dynamics, larval and pollutant transports, and modulation of storm tracks and intensity, and thus have significant environmental, economic, and societal implications. This project, known colloquially as the ‘PEACH’ project (Processes driving Exchange At Cape Hatteras), was a multi-institution effort that deployed a range of observational assets and employed process and realistic numerical modeling to detect shelf edge exchange near Cape Hatteras in response to wind, Gulf Stream, and density variability.

The roles of PIs at Skidaway Institute of Oceanography were to measure surface velocities across the shelf near Cape Hatteras using high resolution WERA HF radar, and to track the evolution of shelf salinity and temperature structure by deploying Slocum shelf gliders north and south of Cape Hatteras. Two bootleg current profiler with bottom CTD moorings were also deployed at the 30m isobath immediately north and immediately south of Cape Hatteras. The ambitious field components of the project were accomplished in Spring
2017 through Fall 2018, and produced an extensive and unprecedented range of datasets. Significant effort went into quality control of datasets, and into combining different data streams into a more complete observational picture of circulation in this complex region than has been possible to date.

Radar observations of surface currents by the paired WERA radars provided high resolution (2-5km horizontally) data revealing complex temporally and spatially variable circulation on the shelf. Combining these WERA data with the longer range CODAR systems operated by collaborators at UNC-CH revealed circulation over the slope and across the entire Gulf Stream immediately north and south of Cape Hatteras, from which to assess relationships between its variability (position and alongshelf curvature) and shelf circulation response. The subcontract with Georgia Tech has continued to improve the Glider Environment Networked Information System (GENIoS),
taking advantage of the combined WERA/CODAR fields, and developing flow partitioning strategies and recasting the optimization problem into belief space.  The glider data itself reveals complicated, multi-layered vertical structure along the Gulf Stream and Hatteras Fronts, with periodic strong salinity intrusions onto the shelf and as many as five layers with interleaving temperature and salinity characteristics in just 20-30 m water depth. These interleaving layers of different T-S characteristics suggest that these
layers arise due to motion along isopycnals, which leads to a net transport of heat or salt. In addition to the listed publications, analysis and integration of results with collaborators is continuing.

This project included a great deal of outreach work at multiple levels, from news, film, and online stories aimed at the general public, to open house/demo activities to let people put hands on the instruments, to outreach games in the classroom, to real time incorporation of data into ocean and atmospheric models. Significantly, the gliders collected real time data that has improved both the state of hurricane modeling and its predictions in real time. The project also entrained filmmaker Kyle Maddux-Lawrence of MADLAW Media, who constructed a film entitled "Beyond the Gulf Stream" based on this project. The 11-minute film includes footage from one cruise and interviews with project scientists, and examines Cape Hatteras, life at sea, and why and how research is done, the scientific process and connections to society. To date, the film has been shown at the 2020 Woods Hole Film Festival, and online through outreach activities. Several technicians, one postdoc, and two Georgia Tech PhD students were trained in glider and radar
operations, contributing to their professional training and development of two engineering PhD theses.

Last Modified: 05/03/2023
Modified by: Catherine R Edwards