EXCHANGE STUDIES 



I. OBJECTIVE 



The purpose of the exchange studies is to quantify the horizontal (alongshore and cross- 

 shelf) and vertical (air- sea, water column, benthic boundary layer, sediment column) fluxes of 

 carbon, including dissolved and particulate forms of organic and inorganic carbon. These 

 measurements will be linked to studies of the biological and biogeochemical processes that 

 transform carbon in order to assess the net flux of carbon through this coastal ocean system. 



II. COMPONENT STUDIES AND RATIONALE 



A. Shelf/Estuaries Exchanges 



In eastern North America, estuaries are the principle avenues of exchange of solutes and 

 particles between the continents and the coastal ocean. To address the fate of carbon produced 

 on the shelves, we must quantify the sign and magnitude of the carbon exchanges between the 

 shelf and estuarine systems. Appropriate sampling of temperature, salinity, PCO2, alkalinity, 

 nutrients, organic carbon and nitrogen, terrestrial biomarkers, and pigments of the Chesapeake 

 Bay would provide information about the estuarine-shelf exchange terms for carbon and 

 nitrogen. In addition, assessment of sedimentary burial rates in conjunction with local carbon 

 budget studies would constrain the long-term sequestration of shelf-derived carbon in the 

 estuarine systems. 



Alkalinity is a measure of ionic charge balance in seawater and river waters. River 

 waters have alkalinity values markedly different form that of seawater (2300 |aeq/kg), with 

 some rivers having values up to three times that of normal seawater. Since PCO2 in seawater 

 depends on alkalinity as well as temperature and total CO2 concentration, the spatial and 

 temporal distribution of riverine water influences the areal distribution of the oceanic CO2 flux. 



Major estuaries (Hudson, Delaware, and Chesapeake) along the northeast coast of the US 

 may contribute refractory dissolved organic matter (DOM) and particulate organic matter 

 (POM) to the shelf that is subsequently exported by along shelf transport to Hatteras, or by 

 cross shelf exchange. Indeed, mass balance calculations suggest that a significant fraction of 

 refractory DOM in the deep ocean could be supplied by fluvial inputs. Terrestrial and marine 

 sources of DOM have distinctive C and N isotopic values, and may be distinguished by 

 characteristic biomarkers (e.g. lignin, cellulose, sterols, and certain aromatic compounds, etc). 

 The recent introduction of compound-specific stable C isotope ratio GCMS analyses, and ^"^C 

 analyses provides a means for identifying source components of DOM at a more detailed level 

 than has been previously possible. These approaches are helping to integrate data from 

 molecular level studies with total (bulk) carbon analyses by using isotope and carbon mass 

 balance and statistical treatments of whole sample pyrolysis or NMR techniques. 



The qualitative influence of terrestrial organic matter on DOM and POM should be 

 readily observed in molecular level studies of DOM composition. These analyses can be made 

 on samples along a salinity gradient from the mouth of major estuarine systems to the shelf 

 water. Quantitative evaluation of the terrestrial component of DOM and POM is more 

 difficult, but may be attempted using a multiparameter approach. 



