precision of about +/- 0.06% using a coulometric titration technique. The high precision 

 attainable with this technique will allow it to be used in biological incubation experiments 

 (which are described in the section on transformations) in addition to the routine water-column 

 concentration measurements. 



The PCO2 of surface seawater will be determined using a continuous flow-through 

 seawater-air equilibrator and infrared analyzer. Such an analysis system will be installed on 

 ships to be used for both hydrographic transect cruises and buoy deployment/servicing cruises, 

 in order to give improved temporal and spatial resolution. Preliminary measurements in the 

 study area have revealed intensely undersaturated areas associated with waters discharging 

 from the Chesapeake Bay (pC02 as low as 116 |iatm, approximately 1/3 of the saturation 

 value), making this increased resolution vital. Atmospheric CO2 concentrations will be 

 measured frequentiy (at least daily during the cruises) using the same infrared analyzers, to 

 allow the air- sea PCO2 differences to be calculated. 



The PCO2 in discrete samples of subsurface waters will be measured during all 

 hydrographic transect cruises. PCO2 is highly sensitive to changes in DIC concentration and 

 can be measured with gas chromatographic techniques with a precision of +/- 0.2%. This 

 allows smaller changes in DIC to be detected than can be done by measuring DIC directiy. In 

 addition, the measurement of DIC and PCO2 on the same water samples fully determines the 

 carbonate system, including the carbonate alkalinity and pH. 



Methane is of interest as both an atmospheric "greenhouse" gas and as a contributor to 

 organic carbon loss from the study area, being formed by microbial processes in sediments and 

 released to the overlying water column, from which it can be lost to the atmosphere by gas 

 exchange. Although not commonly measured, it can be determined with great sensitivity using 

 the same gas chromatograph (equipped with flame ionization detector) used in the 

 determination of discrete PCO2, and thus the analysis is essentially "free" and does not require 

 any additional time for sampling or analysis. 



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

 seawater, it decreases primarily due to the formation of biogenic CaCOs within the water 

 column and increases due to the its dissolution within the underlying sediments. In addition, 

 river waters often have alkalinity values markedly different from seawater, with some rivers 

 having values three times as high as normal seawater. Thus alkalinity measurements serve to 

 estimate the amount of biogeiuc carbonate formation or dissolution which has affected a parcel 

 of water, and as a tracer for river water. Also, since alkalinity strongly affects the relative 

 proportions of the various inorganic carbon species, the PCO2 and hence oceaiuc CO2 

 sink/source area distributions are strongly influenced by these biological and mixing processes. 



DOM is the largest reservoir of reactive carbon in shelf water. Concentrations of DOC 

 probably average 80-90 [Lm, typical of oceanic surface waters. Periodic pulses of DOC to 

 concentrations in excess of 120 |im may follow blooms in phytoplankton production. Such 

 pulses have been occasionally observed, but need to be studied in further. DOC may be 

 routinely measured by high temperature catalytic oxidation (HTCO). The measurement of 

 DOC by HTCO has been intensively studied over the past few years. While there is now 

 general agreement that the technique can yield highly precise and probably accurate values for 

 DOC, care needs to be exercised to minimize problems with contamination, instrument blanks 

 and analytical artifacts. DON can also be measured by high temperature methods. Methods 

 for DON analyses have not undergone the intensive scrutiny and intercalibration that DOC 



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