Radionuclides As Tracers Of Water Fronts In The South Indian Ocean-Antares Iv Results
Résumé
Anthropogenic Sr-90, Pu-239,Pu-240 and Am-241 were used as tracers of water mass circulation in the Crozet Basin of the South Indian Ocean, represented by three main water fronts-Agulhas (AF), Subtropical (STF) and Subantarctic (SAF). Higher Sr-90 concentrations observed north of 43A degrees S were due to the influence of AF and STF, which are associated with the south branch of the Subtropical gyre, which acts as a reservoir of radionuclides transported from the North to the South Indian Ocean. On the other hand, the region south of 43A degrees S has been influenced by SAF, bringing to the Crozet Basin Antarctic waters with lower radionuclide concentrations. The Pu-238/Pu-239,Pu-240 activity ratios observed in water and zooplankton samples indicated that, even 35 years after the injection of Pu-238 to the Indian Ocean from the burn-up of the SNAP-9A satellite, the increased levels of Pu-238 in surface water and zooplankton are still well visible. The radionuclide concentrations in seawater and their availability to zooplankton are responsible for the observed Po-210, Pu-239,Pu-240 and Am-241 levels in zooplankton.