Annual Rep ort of RADARC, 2002

The spatial and temporal distributions of the anthropogenic radionuclides ¹³⁷Cs and ⁹⁰Sr, originating from nuclear bomb testing, the Sellafield reprocessing plants in the Irish Sea, the Ob and Yenisey river discharges, are simulated using a global version of the Miami Isopycnic Co-ordinate Ocean Model (MICOM). The physical model is forced with daily atmospheric re-analyses fields for the period 1950 to present. It is shown that the radionuclides from the Sellafield discharge reach the Barents Sea region after 4-5 years, in accordance with observations. The simulation provides a detailed distribution and evolution of the radionuclides over the integration time. For the Atlantic waters o the coast of Norway and in the southern Barents Sea, the atmospheric fallout dominates over of Sellafield release up to the mid 1960s and from the early 1990s, whereas Sellafield is the main source for the two radionuclides in the 1970s and 1980s. The Ob river discharge dominate the surface ⁹⁰Sr over most of the Arctic Ocean and along the eastern and western coasts of the Greenland before 1960. During the period of 1980 to 1990, the atmospheric fallout and the Ob river discharge are equally important in the ⁹⁰Sr distribution over the Arctic Ocean. It is furthermore argued that model systems like the one presented here can be used for future prediction of radioactive contamination in the Nordic Seas and the Arctic Ocean, for instance under various global warming scenarios