On the Dissolved Carbon in Sea Water

Abstract

Both inorganic and organic carbon dissolved in sea water were studied. New equations concerningthe dissociation of carbonic acid in sea water were introduced which enabled the calculationof each concentration of free carbonic acid, bicarbonate and carbonate ions. By these equations, the quantitative relation between carbonate alkalinity (CA) and total inorganic carbon concentration (C) was obtained. In addition, equations to estimate ratio of simultaneous changes in carbonate alkalinity and calcium content were given which indicate that the ratio is not constant (0.5), but changes widely from 0.1 to 1.0.
It is considered that total content of carbon dissolved in inorganic and organic forms is nearly constant in the entire ocean owing to longer residence time of carbon in the ocean.
It is postulated that the concentration of both inorganic and organic carbon can be expressed as a sum of each own constant term (primary concentration) and variable terms relating to biological and biochemical effects. The constancy of total carbon concentration was proved experimentally by employing dry combustion method of analysis of organic carbon.
In the upper layer (0-1,000 m), carbon concentration is mainly controlled by biological production including shell formation, while in deep layer, by oxidative decomposition of organic matters and solution of calcium carbonate. The concentrations of inorganic and organic carbon in the upper layer are 1.9 to 2.1 mg at/kg and 0.27 to 0.35 mg at/kg respectively. In deep layers, 2.2 to 2.35 mg at/kg for inorganic and 0.07 to 0.10 mg at/kg for organic carbon. It was estimated thatprimary concentrations of inorganic and organic carbon are respectively 2.15 mg at/kg and 0.26mg at/kg, and the total concentration of dissolved carbon is 2.41 mg at/kg. Since two atoms of oxygen forms one molecule of carbon dioxide, and 80% of AOU is used for oxidation of organic carbon, 0.4 AOU is consumed through reproduction of inorganic carbon. The ratio of analytical results of organic carbon by dry combustion and wet oxidation methods was about 2.5 near the surface and 1.3-1.4 in middle and deep layers.
In the last chapter, equations to express the ratio of inorganic carbon and nitrogen concentration were deduced which agreed well with observations. As to organic carbon and nitrogen, the constantratio of 9.3 was proposed. Finally, it was suggested in this paper to revise substantially socalled radio-carbon age of sea water.