Measuring Oceanic Carbon Dioxide

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Te ocean carbon dioxide system is important on the carbon cycle in the earth. It is estimated ocean uptakes about 30% of the anthoropogenic carbon dioxede. However, change of oceanic carbon dioxide system owing to the anthoropogenic carbon dioxede is too small to detect conveniently because the ocean contains more than 50 times as much carbon as the atmosphere. The ocean carbon dioxide system is investigated by the temporal and spatial variations of fugacity of dissolved carbon dioxede [fCCO_2)], total carbon dioxide, pH,alkalinity, ratio of stable carbon isotopes, etc. These data should be highly precise and accurate to detect the change in the earth's environment. Recent developments in analytical chemistry make it possible to reduce the random errors. However, the systematic errors between institutes or scientists are often serious, but not well known. In this study, we discussed most precise and accurate method of oceanic carbon dioxide measurements under any conditions and standar … More d materials to decrease of the systematic errors with the researchers in the world and conducted an intercomparison of analytical works with Institute of Ocean Sciences (IOS) in Canada.The f(CO_2) value of seawater is commonly obtained by the determination of the air equilibrated with sample seawater using the showering type equilibrator and detected with ND= It was known the pressure inside this type equilibrator has to be controlled in order to obtain high accurate f(CO_2) value because the f(CO_2) value is affected by the pressure inside the equilibrate.Standard materials are necessarily for the highly precise measurements of total carbon dioxide, pH,alkalinity and ratio of stable carbon isotopes. The standards for pH and total carbon dioxide developed by Dickson were useful, but standard for alkalinity measurement has been still under the discussion. Intercomparison of stable carbon isotope measurement using the standard for total carbon analysis was conducted by C.S.Wong. However, it was not enough to detect the small change induced anthoropogenic carbon dioxide.Results of the intercomparison with IOS are as follows : (1) the f(CO_2) value obtained by the equilibrator of Hokkaido University was same as that by IOS's equilibrator, (2) difference between amounts of total carbon dioxide measured by Hokkaido University and by IOS was about 10mumole/l, (3) there were systematic errors between pH values obtained by Hokkaido University and these by IOS doe to instrument's standardization and (4) ratios of stable carbon isotopes of bottled Seawater samples and carbonates prepared by Hokkaido University were about 0.7%。 deferent from these analyzed at IOS. Less