Measures of specific surface area and organic carbon will allow testing of the hypothesis that 

 organic matter burial in this region is controlled completely by the supply of mineral surface 

 area to the depocenters. In other words, the correlation often found between sedimentation rate 

 and organic carbon biuial is indicative of a direct control of organic matter preservation by 

 mineral surfaces. Presence of organic carbon concentrations above the monolayer-equivalent 

 level (e.g., at the 900 m depocenter site) would provide an indicator of abnormally high input 

 of organic matter to a site; normally such high concentrations are found only in high- 

 productivity estuarine areas. Interpretation of organic carbon concentrations in the context of 

 grain size will also allow determination of organic carbon loading extends to greater water 

 depths along the slope off of Cape Hatteras relative to slopes farther north. 



Measurement of the amount of enzymatically hydrolyzable organic compounds provides a 

 direct measure of labile organic matter that fuels benthic communities. Cmrent methods are 

 capable of assessing enzymatically digestible amino acids. Methods that measure analogous 

 fractions of lipids are under development. These analytical approaches could be extended to 

 obtain the stable isotope composition of the labile fractions of organic matter. This approach 

 would provide a higher signalinoise ratio for the presence of organic matter from isotopically 

 distinct sources, one which is not confounded by the presence of older organic matter whose 

 source signal may have been obscured. 



The analysis of specific biomarker compounds may help identify the sources of organic 

 matter, the phases (particulate, dissolved, colloidal) that are important in transporting organic 

 matter and the reactivity, composition and age of the organic matter. Certain compounds, 

 particulately the pigment and lipid compounds, but to some extent the sugars and amino acids, 

 are only found in taxonomically restricted sets of organisms. "Molecular markers" can broadly 

 differentiate between terrestrial and marine organic matter. Such lipid markers include sterols, 

 hydrocarbons, lignins and fatty acids. Biopolymeric markers for source materials are also being 

 recognized. These terrestrial/marine source markers are useful in determining whether organic 

 matter in particles or sediments is firom water column primary production or from a terrestrial 

 source. 



Biomarkers can also be used to determine the rates and transformation pathways of 

 biological and chemical processes such as food web dynamics, remineralization processes, and 

 exchange between particulate, colloidal, and dissolved pools. Moreover, a new level of 

 information is now available through stable carbon isotopic composition of these individual 

 biomarkers. Much higher resolution of the source of the organic matter is potentially available 

 from these compound specific isotope measurements. In addition to the source, the age of 

 individual components can now be addressed by radiocarbon measurements. 



D. Bacterial Production 



Of the various methods available to measure bacterial production, [^H]- thymidine 

 incorporation has become the most widely used. This method estimates the rate of bacterial 

 DNA synthesis and consequentiy the rate of cell division. Some of the assumptions of the 

 thymidine method have been extensively tested with positive results in marine and freshwater 

 environments, while other assumptions remain untested or are disputed. The latter include the 

 specificity of thymidine for DNA, the best way to convert incorporation rates to bacterial 

 production values, and whether thymidine is a reliable predictor of growth rate for all, or only 



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