G. Air/Sea Exchange 



Carbon is also gained and lost via the air-sea exchange of CO2. The CO2 flux is 

 dependent upon the difference in concentration between atmospheric and surface seawater 

 PCO2. Many factors contribute to PCO2 variability in surface ocean waters. Mixed-layer 

 heating and cooling, advective transport, air-sea exchange, biological respiration and 

 photosynthesis, and chemical oxidation and dissolution all act to modulate PCO2 over widely 

 varying spatial and temporal scales. Within the Cape Hatteras region, surface water PCO2 

 variability may be dominated by physical advection of alongshelf and Chesapeake Bay waters. 

 By combining continuous mooring-based measurements of PCO2 with periodic ship based 

 measurements of other carbonate parameters (see below), we can begin to deconvolve the 

 mechanisms controlling CO2 gas exchange in the Cape Hatteras region. 



m. METHODOLOGIES 



A. Moorings and Remote Sensing 



The mooring array is designed to answer questions regarding physical processes that 

 affect the distribution of organic carbon within the system. Three cross-shelf transects of 

 moorings (designated as mooring transects 1, 2 and 3 arranged from N to S, Fig. 1) were 

 selected to address both cross- and along-shelf mass transports and the spatial variability in 

 physical structures and dissolved and suspended material including DIC, POC and DOC. It 

 was determined that a series of cross-shelf transects would better address questions regarding 

 along-shelf transport, as opposed to an approach based on a "picket-fence" line of moorings 

 following the shelf edge. The latter would be strongly influenced by the east-west movements 

 of the shelf-edge front, and would not allow for along-shelf flow/exchange calculations. The 

 location of these transects also allows us to examine the POC/DOC content of water 

 influenced by Chesapeake Bay run-off (inner-shelf stations) and water which is unaffected by 

 the Bay (outer-shelf stations). Mooring transect #1 is primarily influenced by the physical 

 processes of the Middle Atlantic Bight, whereas transect #2 is located near the oceanic 

 boundary between the Mid and Southern Atlantic Bights. The third transect is intended to 

 monitor the near shore flows and exchanges that are known to occur. 



Continuous time-series measurements of the horizontal flow fields together with 

 temperature and salinity will provide the basis for calculating cross-shelf and along-shelf 

 transports of volume, heat, and salt in the study area. Calculations of exchanges between the 

 shelf and slope and between the Mid and South Atlantic Bights will be based on concentration 

 differences between and along transects. From previously collected physical data sets, we 

 know that between the northern transect and the middle transect, much of the shelf water will 

 exit the shelf. Therefore, carbon export values may be calculated from POC/DOC 

 measurements and time-series flow data taken along the transects. 



A set of complementary and overlapping moored instruments will provide velocity and 

 water property measurements throughout the water column. Instrumented bottom tripods will 

 address bottom boundary layer processes. Meteorological buoys, with upper-ocean E-M current 

 meters attached, will be used to quantify air-sea momentum and buoyancy exchanges in this 

 meteorologically-complex domain. Coastal wind and sea level will be obtained from NODC. 



11 



