IAEA'97 expedition to the NW Pacific Ocean; Results of oceanographic and radionuclide investigations of the water column

Povinec, P. P.*; Livingston, H. D.*; Shima, Shigeki*; Aoyama, Michio*; Gastaud, J.*; Goroncy, I.*; Hirose, Katsumi*; Huynh-Ngoc, L.*; Ikeuchi, Yoshihiro*; Ito, Toshimichi ; La Rosa, J.*; Liong Wee Kwong, L.*; Lee, S.-H.*; Moriya, Hiroshi*; Mulsow, S.*; Oregioni, B.*; Pettersson, H.*; Togawa, Orihiko 

An international sampling cruise, IAEA'97, was carried out in 1997 in the NW Pacif1c Ocean. The main results of this study are following: (1) The levels of oceanographic parameter showed differences from the historical data, (2) Transuranics water profiles showed typical sub-surface concentration maxima with decrease in concentration by about a factor of 4 from the historical results, deepening their positions by about a factor of 2 and declining the water column inventory by about 20% over 24 years, (3) Sr-90 and Cs-137 data confirmed that the observed changes in concentration profiles have been resulting from the regional water masses circulation, and (4) The concentrations of these radionuclides in surface water after 40 years of their main introduction to the NW Pacific are still showing a latitudinal dependence. The results present the most comprehensive recent study on the distribution of radionuclides in the NW Pacific Ocean with the implications for behaviour of these radionuclides in the water column and physical forcing of water mass circulation over the last 24 years.