What are the physical forces which control carbon export off Hatteras? 



In this document we describe in some detail the experimental approaches which will be 

 used in the OMP to answer these questions. The experiment must address the exchanges and 

 transformations of carbon in the coastal ocean, from bidirectional exchanges between the shelf 

 system and atmospheric, terrestrial and marine sources, to long-term accumulation of carbon in 

 sediments and the ocean interior. As such, this document is divided into an exchanges section, 

 which addresses the processes that result in transport of carbon across internal or external 

 boundaries of the coastal ocean, and a transformations section, which includes the biological, 

 chemical and physical processes that alter the form of carbon within the coastal ocean. 



Two complementary strategies will be applied to the problem of measuring carbon 

 exchange and transformation processes. Semi-continuous measurements of some key 

 parameters will be obtained from instrumented moorings equipped with automated, high- 

 frequency measuring devices. Other biogeochemical parameters and process rates must be 

 measured discontinuously from ships. The OMP field studies have been designed to bridge 

 the gap between mooring- and ship-based measurement strategies. 



The Ocean Margins Program will explicitly link instrumented moorings with 

 comprehensive biological/chemical/physical cruises focused on characterization of the detailed 

 workings of the carbon cycle. This linkage will include a concentration of ship-based 

 sampling within a region bounded by mooring sites, with overlapping measurements acquired 

 from both ships and moored instruments. For example, ship-based measurements of 

 chlorophyll concentrations and photosynthesis rates are coupled with fast-repetition fluorometer 

 (FRR) measurements of the same parameters, collected from both ships and moorings. 

 Similarly, zooplankton biomass measurements based on net tows are coupled with biomass 

 estimates based on the acoustic backscatter recorded by moored acoustic Doppler current 

 profilers (ADCP). 



Moored instruments also will acquire measurements of integrating parameters that 

 represent the net result of complex biogeochemical processes best studied from ships. For 

 example, oxygen concentration will be measured by both moored and ship-based instruments. 

 Changes in oxygen saturation integrate the effects of biological processes that produce and 

 consume oxygen. Time series data on oxygen concentration obtained from moored 

 instruments will be related to ship-based measurements of these autotrophic and heterotrophic 

 processes, including direct respirometry measurements. Sediment accumulations also integrate 

 the net results of processes influencing carbon fluxes and provide an historical record for 

 assessing temporal changes. 



In addition to providing coverage over longer time scales than are sampled by cruises, 

 moorings provide high resolution temporal data which can be used to understand the 

 importance of episodic events on the margin carbon cycle. If episodic events are significant, 

 then the margin carbon cycle may be especially sensitive to man-made pertiirbations which 

 have not been considered in previous models. 



Comprehensive field studies will be logistically constrained to detailed coverage over a 

 relatively restricted spatial scale determined by the design of the mooring array. Such studies 

 will require sampling in different seasonal conditions within a single year. In addition, as 

 confidence is gained in many of the new techniques and instrumentation proposed here, repeat 

 cruises or process specific studies should be conducted in following years. At the start of the 



