Calculation of artificial radionuclides in the ocean by an ocean general circulation model

The concentrations of three artificial radionuclides (Sr-90, Cs-137 and Pu2 39+240) introduced into seawaters from global fallout were simulated from 1 957 to 1994 by using an ocean general circulation model. The distributions of the calculated Cs-137 and Sr-90 concentrations were in good agreement wi th the observed concentrations. The vertical distribution of the calculated Pu239+240 concentration in the South Pacific also agreed with the observed data. However, the calculated Pu239+240 concentrations in the North Pacifi c water columns were significantly underestimated in comparison with the ob served data, which strongly suggests the presence of additional sources of plutonium input to the North Pacific.