vivo fluorescence and transmissometry measurements. Using active fluorescence, it is possible 

 to derive rates of phytoplankton photosynthesis. Depth-resolved time series information about 

 the irradiance field and pigment biomass can be used to support primary production models. 

 This time-series capability will allow the identification of episodic high-productivity events. 

 Inadequate sampling of such events can lead to underestimation of regional primary 

 production. Since primary production over the continental margins is both high and more 

 variable than in the open ocean, there is a clear need for high- resolution temporal and spatial 

 information. 



B. Respiration 



Photosynthesis and respiratory metabolism of organic matter are major determinants of 

 the vertical distribution of carbon in the ocean. The gradients of organic and inorganic carbon 

 created by these two processes in turn affect the exchange rates of CO2 between the ocean and 

 the atmosphere. The rate of respiration of organic matter in the water column also regulates 

 the supply of organic matter to the ocean's interior ("biological pumping") and ultimately the 

 benthos. While much research has focused on the production of organic matter, there are still 

 surprisingly few direct measurements of respiration rates in the ocean. Much of the difficulty 

 associated with measuring respiration in the ocean has been due to a lack of precision in 

 determining the small changes in the concentration of dissolved oxygen or CO2 in samples 

 over short periods time. Using commercially available automatic titrators with potentiometric 

 end point determination it is now possible to accurately and precisely determine small changes 

 (<1 |iM/h) in dissolved oxygen. Likewise, small changes (1 ^iM) in DIG can now be routinely 

 detected by coulometry. In either case, the measurements will reflect the net respiratory 

 activity of the community. 



The net flux of carbon dioxide across the air-sea interface is most strongly affected by the 

 net transformation of carbon between inorganic and organic forms. Therefore, it will be 

 important to make robust, long-term estimates of net community production and respiration in 

 the water column, BBL and sediments. Such transformations are likely to be episodic and 

 temporally variable, and continuous measurements and/or tracer measurements will therefore 

 be required. In the Ocean Margins Program, we will take advantage of the heavily 

 instrumented moorings and new technologies, especially in applying a multiple tracer approach 

 based on in-situ measurements of p02, pN2, and pC02. 



C. Heterotrophic Bacterial Production 



Bacterial turnover and metabolic activity are now generally accepted as crucial and often 

 dominant processes which drive major biological and biogeochemical cycles, ranging firom the 

 direct importance of bacteria as a food resource, to a critical role in global carbon and nitrogen 

 budgets and the production and consumption of greenhouse gases. It has become increasingly 

 evident that a large fraction (commonly 20-50%) of oceanic and freshwater primary production 

 cycles through bacterioplankton. Bacteria are primarily responsible for recapture of DOC into 

 particulate form, which can tiien re-enter pelagic and marine food webs. Bacteria are 

 frequentiy the initial, and sometimes the primary route of nutrient and energy cycling in 

 aquatic sediments. As a result of tiiese activities, bacteria mediate much of the oxygen 



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