Recent inputs and budgets of 90Sr, 137Cs, 239,240Pu and 241Am in the northwest Mediterranean Sea

Monthly atmospheric depositional fluxes of Cs-137, Pu-239.240 and Am-241, coupled with measurements of these radionuclides in seawater of the northwest Mediterranean Sea, are presented. Precipitation rates are the dominant factor in controlling the temporal deposition of anthropogenic radionuclides onto the northwest Mediterranean; however, special events such as Saharan dust input bring a significant amount of radionuclides to this area. The average annual deliveries of Cs-137, Pu-238, Pu-239,Pu-240 and Am-241 through the atmosphere into the northwest Mediterranean were 990, 0.9. 22 and 7.9 mBq m(-2), respectively. The corresponding amounts delivered annually into the northwest Mediterranean were 0.02TBq for Pu-239,Pu-240, 0.007 for (241) Am, and 0.84 for Cs-137. The present atmospheric inputs represent about 0.08% for Pu-239,Pu-240, 0.58% for Am-241, and 0.02% for Cs-137 of their water-column inventories. While the present surface Pu-239.240 concentrations in the west Mediterranean have significantly decreased since 1976, those recorded in deeper layers (below 1000m) have increased. The observed differences between the Am-241 and 239.2411Pu profiles have been caused by the different scavenging efficiencies of the two radionuclides, and also by Am-241 in-growth from Pu-241. The activity ratios of Am-241/Pu-239,Pu-240 and Pu-239,Pu-240/Cs-137 through the water column appear to be lower than the global fallout ratio, whereas Cs-137/Sr-90 activity ratios reflect the global fallout ratio. Higher concentrations of Sr-90 and Cs-137 were found in the intermediate layer (200-600 m), where higher salinity and temperature levels prevail. This indicates the intrusion of Levantine Intermediate Water from the Eastern Basin into the northwest Mediterranean Sea. The estimated radionuclide inventories in the water column for 2001 were around 370Bqm(-2) for Cs-137, 2200 for Sr-90, 52 for Pu-239,Pu-240, and 7.0 for Am-241. (C) 2003 Elsevier Ltd. All rights reserved.