In the next grant cycle we plan to work at both the macroscopic and mesoscopic scales: 

 macroscopic scale being the entire Middle Atlantic Bight and mesoscopic being the process/box 

 scale off Hatteras. Macroscopic sampling should include at least 2 cruises, and preferably three, 

 over the spring-summer-fall period. Mesoscopic sampling should be conducted at least once 

 during each season of the year. Experimentation initiated during mesoscopic cruises would entail 

 daily resampling for an initial 2 week period followed with a monthly frequency thereafter. 



We think working across larger shelf gradients (100+km) is essential for following DOM 

 cycling and for comparing one shelf system to another (e.g., international comparisons). 



METHODS AND PLATFORMS 



Our methods center around water collected at sea and processed in our home laboratory. 

 Hydrocasts and large volume pumping from ships are adequate for our purposes of obtaining 

 water. Methods used are state-of-the-art. DON and D0 15 N are being measured using UV 

 oxidation as no HTOC method presently gives quantitative recoveries of added compounds in a 

 variety of coastal waters. 



STRENGTHS AND LIMITATIONS OF PROPOSED RESEARCH 



The strengths of the combined isotope/concentration approach to understanding DOM 

 cycling is the redundancy of multiple measurements on bulk DOM. A strength of our particular 

 program is our interest in DON, which seems to be more dynamic than DOC. A limitation of 

 the macroscopic survey approach is that sampling needs to be frequent, 2-4x/year, to characterize 

 DOM dynamics across and along the shelf to the Hatteras region. We feel that repeated field 

 sampling will probably better reveal natural patterns. So far, we have not had frequent ship time. 



We are conducting mesocosm experiments to test controls of DOM cycling, as this is the 

 kind of information necessary to construct simulation models of shelf C dynamics. Extrapolation 

 of results to other shelf systems will be difficult if not impossible without the aid of mathematical 

 models. 



STATUS OF RESEARCH 



DOM analysis 



We have developed a reference, high temperature sealed tube method for DOC analysis, 

 and have joined three intercalibration exercises designed to show how to and how not to analyze 

 DOC (dissolved organic carbon). The overall conclusion of this community- wide analytical effort 

 seems to be that the older, low temperature wet chemistry techniques for analyzing DOC 

 (including persulfate and UV digestions), were largely adequate. The new high temperature 

 techniques are, however, more rapid and, in the hands of experienced investigators, more precise. 



44 



