Carbonate chemistry of the Sea of Japan

Abstract

The alkalinity and total CO 2 data were collected during the Kuroshio Edge Exchange Processes‐Marginal Sea Studies expedition (July 28 to August 5, 1992) in the Sea of Japan. The concentrations of normalized alkalinity (NTA = TA × 35/ S ) ( S represents salinity) and normalized total CO 2 (NTCO 2 = TCO 2 × 35/ S ) in the deep water are fairly low relative to that of the northwest Pacific Ocean, indicating relatively little CaCO 3 dissolution and organic carbon decomposition in the subsurface waters of the Sea of Japan. A benthic front between the deep water and the bottom water can be characterized by discontinuities of dissolved oxygen and NTCO 2 at about 2000 m. The bottom water is quite homogeneous with θ = 0.1 ± 0.05°C, S = 34.07 ± 0.005, dissolved oxygen = 215 ± 5 μmol/kg, NTA = 2373 ± 5 μmol/kg, and NTCO 2 = 2297 ± 5 μmol/kg. The inorganic carbon/organic carbon ratio shows that about a 15% increase in NTCO 2 of the deep water is contributed by the inorganic CaCO 3 dissolution. This is rather low compared to the open Pacific Ocean values of 30–40%. The degrees of saturation with respect to calcite and aragonite show that the deep water is undersaturated with respect to calcite below 1300 m. The water below 300 m is undersaturated with respect to aragonite. Excess CO 2 is present from surface to bottom, confirming rapid turnover of the Sea of Japan deep water (100 years turnover time) reported previously based on tritium, fréons 11, 12, and 226 Ra data. Previous age estimation of 300 years for deep waters based on 14 C data was inconsistent with the above results. Recalculation based on proper prebomb Δ 14 C value gives an age of about 120 years for deep Sea of Japan water. Overall, the Sea of Japan contains 3.1±0.5×10 14 g excess carbon.