TRANSFORMATION STUDIES 



I. OBJECTIVE 



The Ocean Margins Program will employ an integrated set of measurements designed to 

 address the major transformations of carbon, often from a number of different perspectives. 

 The purpose is to evaluate the rates of these transformations as they occur in the coastal 

 waters of the Cape Hatteras study region. By coupling these studies with measurements from 

 broad shelf survey cruises, we will be able to assess the potential and mechanisms for long- 

 term removal of carbon from the atmosphere to the ocean in this ocean margin system. 



n. COMPONENT STUDIES AND RATIONALE 



A. Primary Production 



Primary production, the transformation of DIC to POC, is a key transformation and the 

 most important mechanism by which carbon dioxide enters the pool of particulate organic 

 matter. New primary production in the shelf system is constrained by nutrient supply rates 

 from shelf/slope and shelf/estuary exchange processes, atmospheric deposition, and benthic and 

 water column supply processes. Considerable seasonal variations in phytoplankton carbon 

 characterize shelf waters of the U.S. east coast, the most prominent being the spring 

 phytoplankton bloom. The physical oceanography of these waters is believed to be largely 

 responsible for this variability, by determining the residence time of nutrients and resulting 

 phytoplankton within the euphotic zone. Short residence times, on the order of days-weeks, 

 provide ample time for phytoplankton growth, but only grazers with explosive growth potential 

 (e.g. protozoan and gelatinous metazoan zooplankton) develop quickly enough to consume 

 such blooms. In the absence of such rapid grazing responses, substantial portions of 

 phytoplankton carbon may sediment or cascade off the outer shelf. Longer residence times of 

 weeks-months allows POC to be cycled and transformed, for example via bacterial activity and 

 zooplankton grazing, prior to being removed from the water column by deposition or 

 advection. Since the euphotic zone may extend to the seafloor at certain locations and times of 

 the year, benthic primary production and nutrient dynamics may contribute and influence the 

 integrated shelf DIC to POC transformation rate. The net loss or gain of carbon in the coastal 

 ocean is determined by the balance of these transformation processes. 



Although it is critically important to understand the rates of carbon fixation and 

 subsequent transformations, it is equally important to assess the composition of the 

 phytoplankton community. It has often been observed that blooms of larger cells, such as 

 diatoms, can lead to significant export of intact cells to the underlying sediments, while 

 blooms of smaller organisms can lead to cycling of carbon within the microbial food web. In 

 addition, blooms of coccolithophorids export carbonate from the upper water column to the 

 sediments. Thus it is important to determine the relative importance of each component of the 

 phytoplankton to the community primary production. 



Optical measurements can be used to infer temporal and spatial patterns in pigments, 

 particulates and primary production and provide increased vertical resolution of water column 

 biological properties. Discrete measurements of biomass can be extrapolated on the basis of in 



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