RAPID: Collaborative Research: HF Radar Surface Current Measurements in Support of Constraining Shelf Edge Exchange in the SAB Under Wind, Tidal and Gulf Stream Influence

This is a RAPID award, evaluated and funded on an accelerated schedule because of critical time pressures.

A recently funded proposal (NSF-OCE biological and physical oceanography programs, Awards 1032285 and 1032276) by Jim Nelson, H. Seim and C. Edwards focuses on physical-biological coupling during winter on the outer shelf/upper slope off Long Bay (between Cape Romain, SC and Cape Fear, NC. In this region, elongated shelf-edge phytoplankton bloom features are common occurrences in wintertime satellite imagery. Unlike other sections of the South Atlantic Bight shelf, where shelf edge upwelling associated with Gulf Stream frontal eddies is the largest source of nutrients supporting new production on the shelf, it appears that in Long Bay, other processes must sustain the phytoplankton blooms throughout the winter months. The Nelson et al. work will use mooring, glider, ship and satellite measurements to investigate both physical and biological aspects of these other shelf-edge physical mechanisms. This project will expand upon the scope of science made possible by their suite of measurements by adding long-range HF radar surface current measurements to the experiment, using existing HF radar instrumentation available for this work. Deployment of the radars will enable the collection of data on surface ocean current with a spatial resolution of 3000m and with a temporal frequency of 30 min and over ranges reaching the Gulf Stream.

Two beam forming, Wellen Radars (WERA) are available at the University of South Carolina (Voulgaros) for use in this project. A primary reason this deployment is suitable as a RAPID project is that one of the two radars has only recently become available as a result of unanticipated down-time in its dedicated mission as part of the national HF-radar network. It would not have been possible to commit this radar to the Nelson et al project at the time of their original proposal, but this interruption in operation makes the system temporarily available for a focused scientific research deployment. Necessary tasks for this deployment, such as modifying the frequency of one of the radars, obtaining radio licenses from the FCC, and finding suitable locations and obtaining permissions need to be started quickly so as to deploy these systems in time for concurrent operation with the Nelson et al. scheduled deployment in late January 2012.

Intellectual Merit The proposed data collection will contribute substantially to the funded Nelson et al. work by providing a significant improvement in their capacity to define Gulf Stream offshore position and orientation at high spatial and temporal resolution. Assuming availability of internet communications at the installations, real-time surface current maps can contribute to the ship and glider operations of the Nelson et al. project. With the addition of the Long Bay radar deployments to the existing IOOS-supported radar coverage on the Georgia shelf, it will be possible to contrast the surface expression of wind-forced alongshelf flow, internal tides and shelf edge eddies between the Georgia shelf and Long Bay, and determine their correspondence with different modes of Gulf Stream variability. This will further permit the assessment of alongshelf convergence and off shelf import/export between these contrasting regions of wind and Gulf Stream influence at larger scales than have been possible in the past.

Broader Impacts Newly defined denitrification processes (sinks) in the global coastal ocean imply much higher fixation and input rates (sources) than are presently identified, requiring a more accurate accounting of nitrate sources at the shelf edge. The export of shelf derived carbon sources and the import of nitrate into the coastal ocean are both poorly constrained in the South Atlantic Bight, and may contribute to global carbon and nutrient cycles in important ways. These measurements will better constrain those contributions for winter forcing in this region. This collaboration will also enhance collaboration between the neighboring states of North Carolina, South Carolina and Georgia, leading to a potential regional synergy in the area of Physical Oceanography that could benefit all three regions.