B. Lateral Fluxes - Cross-shelf and Shelf-slope Exchanges 



Quantitative assessment of cross-shelf and shelf-slope exchanges will require 

 determination of the transport of dissolved and particulate organic matter within the water 

 column and benthic boundary layer. The quantitative distribution and particulate organic 

 carbon (POC) content of suspended particles and particle aggregates will be measured across 

 the shelf and upper slope. These data combined with information on water volume transport, 

 near-bottom flow, and measured POC fluxes into sediment traps deployed in the slope region 

 will be used to quantify the flux of particulate organic carbon from the shelf and across the 

 slope. The deep water POC fluxes extrapolated from aggregate abundance profiles and 

 measured by the sediment traps will be integrated with the benthic flux measurements to 

 provide estimates of nutrient regeneration occurring at the sediment water interface. Off-shelf 

 transport will also be indirectiy estimated by assessing the deposition of shelf-produced 

 organic matter on the adjacent continental slope and rise. 



The BBL could be a conduit through which a significant quantity of POC is carried off 

 continental shelves. Previous studies over the Middle Atiantic Bight (MAB) shelf have not 

 resolved near-bottom flow or particulate concentration to the extent necessary for reasonable 

 estimates of POC transport through the BBL. However, they have shown that shelf sediments 

 of the MAB are mobilized by a number of processes. Those predominant over the shelf near 

 Cape Hatteras are storm-induced flow (principally wave motions but also wind driven 

 currents), internal waves and the Gulf Stream. Storm-induced currents are dominant in 

 resuspending sediments over the inner and middle shelf, whereas internal waves and Gulf 

 Stream currents are most important in mobilizing sediment at the shelf-edge and upper slope. 



The flux of nutrients and dissolved inorganic carbon (DIC) will be estimated from 

 automated sensor measurements, based on their correlation with proxy measurements such as 

 dissolved O2 saturation and pC02. Preliminary data from the Cape Hatteras region indicate 

 that >95% of the variation in direct measurements of DIC can be predicted from measurements 

 of temperature, salinity and oxygen. The required correlations can be determined during 

 survey cruises, whereas the proxy measurements can be made continuously on moorings. If 

 this approach works well, it will be possible to extend greatiy the time scale and resolution 

 with which nutrient and DIC fluxes can be estimated. 



The loss of DOM generated in the shelf area and subsequentiy exported into the deep 

 ocean basins may constitute a significant mechanism for the sequestering of anthropogenic 

 carbon dioxide from the atmosphere. Thus, it is necessary to quantify changes in the dissolved 

 organic carbon (DOC) pool on the shelf in order to fully characterize the carbon budget This 

 is especially important since the DOC pool is the second largest pool of exchangeable carbon 

 in the oceans (could equal as much as 15% of the DIC), and the one whose magnitude is least 

 well known in absolute terms. While dissolved organic nitrogen (DON) measurements cannot 

 be used to accurately quantify the changes in the carbon pool, because the ratio of DOC/DON 

 varies, changes in DON are useful to help characterize these transformations and to fuUy 

 characterize the nitrogen budget. Biomarker analyses may also prove to be extremely useful 

 in the DOC/DON pools to constrain sources and fluxes of the DOM. 



