Anthropogenic Radionuclides in the Arctic Ocean: Distribution and Pathways

Sammanfattning: Anthropogenic radionuclide concentrations have been determined in seawater and sediment samples collected in 1991, 1994 and 1996 in the Eurasian Arctic shelf and interior. Global fallout, releases from European reprocessing plants and the Chernobyl accident are identified as the three main sources. From measurements in the Eurasian shelf seas it is concluded that the total input of Cs-134, Cs-137 and Sr-90 from these sources has been decreasing during the 1990's, while I-129 has increased. The main fraction of the reprocessing and Chernobyl activity found in Arctic Ocean surface layer is transported form the Barents Sea east along the Eurasian Arctic shelf seas to the Laptev Sea before entering the Nansen Basin. This inflow results in highest Cs-137, I-129 and Sr-90 concentrations in the Arctic Ocean surface layers, and continuously decreasing concentrations with depth. Chernobyl-derived Cs-137 appeared in the central parts of the Arctic Ocean around 1991, and in the mid 1990's the fraction to total Cs-137 was approximately 30 % in the entire Eurasian Arctic region. The transfer times for releases from Sellafield are estimated to be 5-7 years to the SE Barents Sea, 7-9 years to the Kara Sea, 10-11 years to the Laptev Sea and 12-14 years to the central Arctic Ocean. The transfer times for releases from Sellafield are estimated to be 5-7 years to the SE Barents Sea, 7-9 years to the Kara Sea, 10-11 years to the Laptev Sea and 12-14 years to the central Arctic Ocean. Global fallout is the primary source of plutonium with highest concentrations found in the Atlantic layer of the Arctic Ocean. When transported over the shallow shelf seas, particle reactive transuranic elements experience an intense scavenging. A rough estimate shows that approximately 75 % of the plutonium entering the Kara and Laptev Seas are removed to the sediment. High seasonal riverine input of Pu-239,240 is observed near the mouths of the large Russian rivers. Sediment inventories show much higher concentrations on the shelf compared to the deep Arctic Ocean. This is primarily due to the low particle flux in the open ocean.