LAUSR

Vertical distributions of 90Sr and 137Cs in Sea of Japan/East Sea (SOJ/ES) water in the period of 1977-2010 exhibited a typical diffusion shape with surface/subsurface maxima and decreasing values with increasing depth. Apparent vertical diffusion coefficients (AVDCs) and apparent initial surface fluxes (AIFs) of 90Sr and 137Cs, which were estimated using a curve-fitting method from a vertical diffusion model, showed temporal and spatial variability. A diffusion depth introduced for understanding of vertical movements of 90Sr and 137Cs in the SOJ/ES well correlated with corresponding AIFs, suggesting that spatial variations of the 90Sr and 137Cs inventories have been governed by oceanic conditions such as changes in AVDCs, which may be related with eddy field, characterizing the SOJ/ES. The temporal changes of the AVDCs suggest that the production of eddies increased during the 2000s comparing with that in the 1990s. These observations represent the first applications of radionuclides as tracers in production of oceanic eddies.