Concentration and Regeneration of Cd in the Japan Sea Proper Water

The concentration level of cadmium (Cd) and the regeneration related to phosphate (PO₄) were examined at two stations (CM10, CM12) in the eastern Japan Basin in July 1998. The observed Cd concentrations were around 0.2–0.3 nM and 0.5–0.6 nM in the surface and deep layers (Japan Sea Proper Water; JSPW), respectively; the concentration of Cd in the JSPW was much lower than that in the Pacific deep water, which is attributed to its specific formation system (which driven by the winter convection of the surface layer within the Japan Sea, thereafter descending to the deep layer) connected with the relatively active vertical mixing in the Japan Sea. A plot of Cd against PO₄ showed good linearity with positive y-intercept values, suggesting that the excess Cd was apparently not available in the biogeochemical cycle. The molecular ratios of consumed O₂ to regenerated Cd and PO₄ in the JSPW were 688,000, 140 and 881,000, 146 for CM10 and CM12, respectively, and a lower preformed Cd concentration (around 0.37 nM) was also estimated in the JSPW, different from that of the North Pacific deep water (613,000 for Cd, 170 for PO₄, and 0.64 nM of preformed Cd).