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.
In collaboration with lead-PI George Voulgaris at the University of South Carolina, two long-range beam-forming WERA HF Radars were successfully deployed and operating by mid-Feb 2012 overlooking Long Bay, SC. Our objectives included contributing to the separately funded Nelson et al activities there (NSF Awards 1032285 and 1032276). Our data will be especially useful in developing glider guidance algorithms, though collaboration with Edwards (co-PI on the Nelson grant) utilizing spatial patterns of circulation. Data will also assist in Gulf Stream position determination. New research facilitated (but not funded) by data collected under this grant will including examine shelf edge eddies, compare shelf response to wind and Gulf Stream forcing, relative to coastline curvature. We will contrast the GA and Long Bay shelves in each case, as this grant helped continue Georgia radar operation while Long Bay radars operated, to assure comparison was possible. Two ADCP moorings were deployed on the Georgia shelf from Feb-August 2012 (bootlegged), at similar isobaths as the Nelson et al project in Long Bay, and were successfully retrieved. Radar data from both subregions have been quality controlled and preliminary analyses undertaken. Tide correlated eddies on the Long Bay shelf edge have been detected, of similar scale to those on the Georgia shelf. Long Bay eddies appear along southward flowing Gulf Stream filaments at the shelf edge, shoreward of the large seaward deflection of the Gulf Stream. These small eddies are clockwise, in contrast to the counter-clockwise eddies off Georgia. Now have over a year of concurrent radar coverage of two subregions, located immediately upstream and downstream (in the Gulf Stream sense) of the Charleston Bump, and data from several months of mid-shelf and shelf edge moorings in each subregion. This will provide rich research fodder for the near future.