Recent accumulation of trace metals in sediments at the DYFAMED site (Northwestern Mediterranean Sea)

The DYFAMED site (Ligurian Sea, 43 degrees 25'N; 7 degrees 52'E) has been the subject of multidisciplinary research since 1987, including the study of atmospheric deposition of metals and their association with marine particles in the water column. On the other hand, the attention paid to the underlying sediments as the ultimate repository of elements, particularly pollutants, has been considerably lesser. Through the combined use of (210)Pb chronologies and elemental analysis, we studied the concentrations and fluxes of trace metals (Zn, Pb, Ni, Cu, Cr) in a sediment core collected from approximately 2300 m water depth at the seafloor beneath DYFAMED. Surface metal enrichment during the 20th century is apparent in the case of Pb, Zn and Cu (maximum enrichment factors 1.5, 1.2 and 1.4, respectively). A comparison with published data suggests that atmospheric deposition is the main entrance route of anthropogenic trace metals accumulated in the recent sediments, while lateral advection of sediments by currents and sediment gravity flows is proposed to account for the pre-industrial concentrations of metals. Recent atmospheric inputs of Pb and Cu are more efficiently stored in sediments with respect to Zn, most of which is apparently advected elsewhere.