We are continuing development of a D0 15 N technique. As HTOC techniques do not give 

 uniform recoveries, we are relying on UV oxidation both for concentration determinations and 

 for the initial step in collecting N for isotopic determination. 



Offshore cruises 



We joined Dan Repeta and Tim Eglinton of WHOI in April 1993 for a short 5-day cruise 

 to Georges Bank. DOC analyses did not show any marked changes across the Bank, in spite of 

 large changes in algal biomass. We also collected water from Georges Bank and from over 

 benthic cores to check how fast DOM might decay. Overall, rates of decay were very slow, 

 declining less than 25% over six months of incubation. 



In April of this year, we participated in a cruise from Georges Bank to Hatteras. 

 Preliminary results show an increase in DOC near shore and to the south in the Middle Atlantic 

 Bight, suggesting that DOM is exported from estuaries and then off the shelf in the Hatteras 

 region. 



In the upcoming summer cruise to Georges Bank, we will be searching for transient DOC 

 increases that we expect at the end of phytoplankton blooms. Dynamics of DOM decomposition 

 will be examined in water collected from various stages of bloom development. 



Isotope methods development work 



We have expended much of our effort developing routine, reliable methods for analyzing 

 carbon and nitrogen isotopes in DOM. This effort is ongoing. 



We are looking towards a renewal submission (Dec. 1 1993) that emphasizes DON 

 dynamics both in the Hatteras region and along the entire Middle Atlantic Bight. We are 

 interested in labile vs. refractory DON, DON export from estuaries, and rates of DON 

 degradation in situ. The details of the DON cycle are poorly known compared to the growing 

 knowledge about DOC, but DON appears more dynamic than DOC, and may partially control 

 DOC distributions. Our last year of funding includes a heavy emphasis on developing methods 

 for DON analysis. 



Our renewal will also focus on elucidation of the controls of DOM production and 

 decomposition and on the mechanisms that may lead to preferential recycling of N relative to C. 

 Preferential recycling is critical to being able to sequester C on a long term basis. 



At the scale of the entire Middle Atlantic Bight, our renewal will use a combination of 

 concentration and isotopic measurements (DOC, DON, D0 13 C, D0 14 C, D0 15 N, POC, PN, P0 13 C, 



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