Tracing the dispersion of particles from the Rhône River to the Gulf of Lions using plutonium isotopes

Titre du congrès :ASLO Summer Meeting Ville du congrès :Saint-Jacques-de-Compostelle Date du congrès :19/06/2005

The dispersion and fate of terrigenous matter are key points for a better understanding of continental margin processes. Due both to their high affinity for particles and their long half life, Pu isotopes (238Pu, 239,240Pu) are appropriate tracers to follow the dispersion of particulate matter from the Rhône River to the Gulfof Lions (Mediterranean Sea). Most of the 238Pu introduced into the Rhône River were discharged by the Marcoule reprocessing plant since 1958. This work présents a first detailed spatial distribution of Pu isotope concentrations in surface sédiments off the Rhône mouth. Using 137Cs concentrations and their corrélations with Pu isotopes, we are able to give a first estimate of Pu inventories for the sédiments of the study area. The 238Pu balance indicates that at least 85 % of the 238Pu discharged by the Marcoule reprocessing plant are currently trapped in the sédiments close to the Rhône River mouth. Thèse results suggest a low exportation of particulate matter introduced by the Rhône River towards the Gulf of Lions.