Résumé
The aim of this work was to developed field incubations of seawater using isotopically enriched inorganic mercury (199IHg) and monomethylmercury (201MMHg) to understand processes involved in mercury transformations. Experiments were carried out for different sites of the Mediterranean Sea, at coastal and open water stations as a contribution to the MERCYMS project in the framework of the EU ELOISE program. Water incubations were conducted under various controlled conditions (dark and light, filtered and unfiltered water) to assess the major biogeochemical pathways regulating mercury transformations. Biological characteristics of the incubated samples were also monitored through phytoplankton and bacteria diversity. Isotopically enriched species were used as chemical tracers and have allowed the direct determination of specific methylation and demethylation yields. This experimental approach demonstrates that the use of isotopically labeled mercury species offers a unique potential to examine mercury transformation processes in seawater.