Dynamics of the Japan Sea Deep Water Studied with Chemical and Radiochemical Tracers

Abstract

Abstract Chemical and radiochemical tracers have been used to make clear the dynamics of the Japan Sea deep water including its chemical alteration. They are the Si-O combination, tritium, CFCs (trichlorofluoromethane and dichlorodifluoromethane), C-14 and Ra-226. The Si-O diagram method has revealed a small areal variation of the Japan Sea deep water except water in a small basin surrounded by the Yamatotai Rise and its coastal upwelling off Japan. The tritium and Ra-226 combination method is applied to a box model with three layers and four boxes, which is based on the vertical profiles of tracer components including conservative and nutrient elements. The result shows that the turnover time of the Japan Sea water for vertical mixing is about 100 yrs and the residence time of the whole Japan Sea water except the warm Tsushima current water is about 1000 yrs, indicating that the Tsushima current flowing through the Japan Sea makes little interaction with the Japan Sea Proper Water. The difference between the apparent C-14 age of the Japan Sea deep water of 300 years and the turnover time is originated in the delay in the air-sea gas exchange equilibrium of carbon dioxide. The gas transfer velocity has been calculated to be 1.5 m/day. The vertical profiles of CFCs also support the estimated water exchange rates between the reservoirs, but our present data are insufficient to explain their small apparent gas exchange rates less than 0.1 m/day. The oxygen consumption rate of the Japan Sea deep water is nearly equal to that of the Pacific deep water indicating that the Japan Sea is not fertile, while the regeneration rate of silica in the Japan Sea is much larger than that in the Pacific.