Isotopic tracing of anthropogenic Pb inventories and sedimentary fluxes in the Gulf of Lions (NW Mediterranean sea)

Abstract

Lead stable isotopes have been analyzed in 24 box-cores (0–50 cm) from various transects across the Gulf of Lions. Lead concentrations (23–85 ppm) and isotopic signatures ( 206Pb/ 207Pb=1.174−1.188) in surficial sediments clearly show the impact of pollutant lead that constitutes 22–80% of the lead accumulated in the first centimeter of these cores. This anthropogenic input is clearly distinct from the natural detrital lead, which comes with more radiogenic signatures ( 206Pb/ 207Pb=1.195−1.233). This makes stable lead measurements a useful complement to 210Pb or other radioactive tracers in studies of sedimentology and hydrodynamics in coastal environments. Comparison of riverine and atmospheric deposition with lead accumulated in the sediment cores indicates that the Rhône particulate input dominates the lead inventories in the continental shelf sediments. The total pollutant lead accumulated in the Gulf of Lions for the past century amounts to 84,000±18,200 tons. The accumulation of pollutant lead in the surficial sediments is in excess of the riverine and tropospheric input estimated from the literature. This may result from overestimation of pollutant lead accumulation on the continental self, due to insufficient sampling in this region and/or from an additional input from boundary scavenging of lead advected by the Liguro-Provençal current over the shelf.