Anthropogenic radionuclides in the Japan Sea: their distributions and transport processes

The anthropogenic radionuclides, 90Sr, 137Cs and 239+240Pu, were measured in the water column of the Japan Sea/East Sea during 1997–2000. The vertical profiles of radionuclide concentrations showed: exponential decrease with depth for 90Sr and 137Cs, and surface minimum/subsurface maximum for 239+240Pu. These results do not differ substantially from results reported previously. The area-averaged concentrations of radionuclides in the Japan Sea are higher than those found in the Northwest Pacific Ocean below surface layer showing the accumulation of the radionuclides in the deep waters in the Japan Sea. Concerning spatial distributions, the area of high 137Cs inventory extends from the Japan Basin into the Yamato Basin. It is suggested that wintertime convection of water, occurring mainly in the Japan Basin, causes the radionuclides to sink. The nuclides then advect into the Yamato Basin after detouring around the Yamato Rise.