Abstract
The radioactive decay rate of radio-carbon in the ocean (1.5x10-11g/m2, y) is much smaller than the rate of biological uptake and regeneration of inorganic radio-carbon from organic matters (1 x 10-10 g/m2, y)and the exchange rate at the air-sea interface (2 x 10-10 g/m2, y). Therefore, the radio-carbon age of sea water is controlled not only by the radioactive decay but also by the other factors mentioned above. This is the reason for the higher age of the surface water in polar areas.
The radio-carbon age of sea water in the deep layers of the oce a ns is determined by radioactive decay, the exchange of inorganic carbon between the surface and the deep layers and regeneration of the inorganic carbon through biological decomposition. Owing to the smaller concentration of the inorganic carbon at the surface layer than that in the deep layer, the specific activity of radio-carbon in the deep layer tends to decrease through mixing with surface water, which gives a higher radiocarbon age to the deep waters. Results of calculation show that when the residence time of the deep waters is 200 to 300 years and that of the surface water is 5 to 7 years, the apparent age is estimated to be about 1,300 years, which is in good accordance with the observation.
