Carbonate chemistry of the Sea of Japan

Abstract

The alkalinity and total CO2 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 CO2 (NTCO2 = TCO2 × 35/S) in the deep water are fairly low relative to that of the northwest Pacific Ocean, indicating relatively little CaCO3 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 NTCO2 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 NTCO2 = 2297 ± 5 μmol/kg. The inorganic carbon/organic carbon ratio shows that about a 15% increase in NTCO2 of the deep water is contributed by the inorganic CaCO3 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 CO2 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 226Ra data. Previous age estimation of 300 years for deep waters based on 14C data was inconsistent with the above results. Recalculation based on proper prebomb Δ14C value gives an age of about 120 years for deep Sea of Japan water. Overall, the Sea of Japan contains 3.1±0.5×1014 g excess carbon.