HTCO methods have, and making the intercomparability of data collected at different sites by 

 different laboratories less clear. 



Developments in continuous underway or synoptic sampling of DOM include fiber optic 

 analysis of DOM fluorescence, and airborne oceanographic lidar fluorescence in the near UV. 

 DOM concentrations are often linearly related to seawater absorbance, offering the possibility 

 of remote sensing of DOM. However, algorithms are sensitive to the absorption/fluorescence 

 properties of the water body, such that if estuarines make significant contributions to local 

 DOM concentrations, DOM optical properties of the system need to be fully characterized in 

 order to obtain reliable algorithms. Synoptic measurements of DOM are in the early stages of 

 development, but are progressing rapidly. Some data from airborne oceanographic lidar may 

 be useful in the OMP Hatteras study. 



Large volume DOC isolation by ultrafiltration has made mg to g quantities of a colloidal 

 fraction of the DOM available for detailed molecular level analyses. Chemical degradative 

 and NMR studies have shown that approximately 50% of the > 1000 Dalton size firaction is 

 composed of polysaccharides. Chromatographic techniques are currently under study which 

 could further fractionate DOM by size or compound class, such that an even larger percentage 

 of DOM may be characterized by chemical degradative and spectrometric techniques. In- 

 source pyrolysis mass spectrometric analysis has been performed on a few samples of DOM 

 isolated by ultrafiltration, and shows promise as a means for rapid characterization of protein, 

 carbohydrate, and lipid fractions. In combination with on-line gas chromatography and isotope 

 ratio mass spectrometry, this technique may allow us to better characterize the sources of 

 DOM and follow changes in DOM composition along the shelf. 



ii. Particles 

 POC has traditionally been measured or derived from particle mass measurements using 

 nets (primarily collect zooplankton and large particles), water bottles (primarily phytoplankton 

 and small particles), in-situ filtration of large volumes of water, or optical measurements of 

 light scattering or attenuation. Optical methods provide the fastest and cheapest method of 

 determining the distribution of total particles in the water column, but most of the optical 

 signal is generated by the smallest particles, perhaps <20 |J.m. The small-particle mass has 

 traditionally been thought to constitute most of the total mass of particles in the ocean, but 

 recent measurements have shown that 10-50% of the particle mass is in aggregates >0.5 mm, 

 so both large and small particles are significant in computing lateral fluxes off the shelf. 



Large aggregates dominate the settling flux in the ocean and have received increased 

 attention in studying biogeochemical cycles. Sampling these large particles for abundance and 

 size distribution is difficult because traditional methods of determining particle concentration 

 such as light transmission and particle analyzers do not sample a large enough volume of 

 water to obtain statistically accurate data on aggregates. Water bottles can collect aggregates 

 and other large particles (fecal pellets, etc.), but they can settle quickly (in minutes) below the 

 bottie spigots or break up during extraction from the bottle. 



In order to quantify the large particles, camera systems integrated with a CTD and 

 transmissometer will simultaneously collect data on the distribution of suspended particles and 

 aggregates along with the physical structure of the water column. Profiles and horizontal 

 surveys of aggregate abundance allow for the identification of mid-water and benthic aggregate 

 nepheloid layers which might be missed by sediment trap or pump sampling. Downslope 



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