Anthropogenic radionuclides in the Japan Sea; Their distributions and transport processes

Ito, Toshimichi ; Aramaki, Takafumi; Kitamura, Toshikatsu; Otosaka, Shigeyoshi  ; Suzuki, Takashi  ; Togawa, Orihiko ; Kobayashi, Takuya ; Senju, Tomoharu*; Chaykovskaya, E. L.*; Karasev, E. V.*; Lishavskaya, T. S.*; Novichkov, V. P.*; Tkalin, A. V.*; Shcherbinin, A. F.*; Volkov, Y. N.*

The anthropogenic radionuclides, Sr, Cs and Pu, in the seawater column of the Japan Sea were measured during 1997-2000. The vertical profiles of radionuclide concentrations showed their typical features; exponential decrease with depth for the Sr and Cs and surface minimum - subsurface maximum for the Pu, and there are no substantial differences between the present study and the previous ones. The area-averaged concentrations and the inventories of radionuclides in the Japan Sea are higher than those in the Northwest Pacific Ocean. In the spatial distributions, high inventory area extends and intrudes from the Japan Basin into the Yamato Basin. It is suggested that radionuclides sink by the vertical transport occurring mainly in the Japan Basin then advect into the Yamato Basin after detouring around the Yamato Rise, and finally, they are accumulated in the deep seawater of the Japan Sea.