whereas PCO2 is also affected by biocalcification and dissolution of calcium carbonate. 



Because of the shallow nature of shelf systems, a significant proportion of the respiratory 

 oxidation of organic carbon may occur in bottom sediments. Pore water concentrations are 

 sensitive indicators of metabolic reactions occurring in sediments. Reactions that do not 

 produce measurable variations in the chemistry of the solid phase often produce easily 

 observable signals in the pore waters. As such, pore water concentration measurements and 

 complementary reaction rate incubation experiments are necessary to identify the diagenetic 

 processes and reactions that determine the fate of organic materials deposited on the 

 continental shelf sea floor. Furthermore, diffusive and non-diffusive exchange rates of solutes 

 across the sediment-water interface are directiy proportional to the concentration difference 

 between the pore waters and overlying bottom waters. Studies of sea floor exchange rates and 

 processes therefore require pore water concentration measurements. 



Initial measurements will focus on redox sensitive species that are known to participate in 

 the oxidation of organic matter, nutrients, and carbon system parameters. The measured 

 down-core variations in concentrations will be interpreted in terms of the solid phase 

 chemistry, known metabolic and inorganic reactions, and in the context of transport - reaction 

 models. These studies should identify the dominant reactions influencing pore water 

 composition and constrain the relative rates at which the ttansport processes and reactions are 

 occurring. Incubations of sediment samples will provide direct measures of reaction rates 

 permitting total transport and exchange rates to be estimated. These can then be compared to 

 those estimated by other strategies in the program. 



C. Organic Carbon Preservation 



To understand and quantify the sequesttation of organic carbon in continental shelf 

 systems, the properties and processes that retard remineralization and promote preservation 

 must also be identified. Characterization of the solid phase wUl provide measurements 

 necessary to interpret process studies such as organic decay and carbon burial, and provide 

 indicators of the sources of carbon in the sediment. These characterizations wiU form the bulk 

 of measurements to be made in extensive surveys, and will also be performed at the more 

 intensively studied sites focusing on transformations. 



Organic matter will be characterized in terms of total concentrations (TOC, TN) and 

 measurement of labile subfractions that fuel benthic metabolic activity (e.g., enzymatically 

 hydrolyzable compounds). Extensive work on biomarkers will seek to identify the sources of 

 organic matter to the sediment; this work will be supplemented by bulk and compound-specific 

 stable isotope measurements. Characterization of the refractory macromolecular materials will 

 help clarify reasons for survival of organic matter during burial. Analysis of metal oxide and 

 sulfur concentrations will provide evidence for the dynamics of metabolic oxidants and 

 products. 



Calcium carbonate concentrations wiU be measured to assess the importance of this form 

 of carbon in both seasonally varying processes and long-term burial. Other mineralogical 

 studies will allow interpretation of the origin of the sediments and diagenetic reactions that are 

 associated with metabolic activities. 



The organic matter-grain size relationships that define monolayer-equivalent 

 concentrations need to be measured on cores used to determine shelf-slope burial rates. 



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