Modelling the dispersion and scavenging of plutonium in marine systems

An Oceanic General Circulation Model (OGCM) has been developed for modelling the dispersion of plutonium (Pu) and other non-conservative tracers in the marine system. A plutonium scavenging model as well as an advection-diffusion model has been incorporated into the OGCM. It appears that the best way to validate a numerical model for the dispersion of non-conservative tracers in the global ocean would be to calculate radionuclide concentrations in the ocean from atmospheric nuclear tests (global and local fallout) and to compare them with observations. This paper concentrates on predictions of the distributions and vertical profiles of 239,240Pu in the water column of the Pacific Ocean, both from global fallout as well as from local fallout from nuclear weapons tests at Bikini and Enewetak Atolls. The water profile concentrations, water and sediment inventories of 239,240Pu have shown generally good agreement between calculated and observed data. Nevertheless, the present model cannot calculate the water profiles in the north North Pacific or the west coast of the American continent very well, mainly because of the underestimation of the effect of biological productivity on Pu scavenging and its removal from the water column in these regions. (author)