Meso and small-scale variations of 210Pb fluxes on the Northwestern Mediterranean continental margins

210Pb was analysed in samples collected from (16) sediment traps, deployed during 1 year on the Northwestern Mediterranean continental margins, within the framework of the (MTP I)-EUROMARGE-NB programme. The traps were moored within (5) submarine canyons and their adjacent open slope, corresponding to contrasting conditions of particle inputs (fluxes and constituents). The major meso-scale observation (at the margin) is the variation in 210Pb fluxes along the slope, increasing by a factor of 2–3 between the entrance and the exit of the slope, in relation to the general (water) circulation. At a smaller scale (canyon), the 210Pb fluxes showed trends which were common to the various sites, i.e. a seaward decrease at 500 m depth and an increase, with depth, in the canyons. All these features are related to mass flux variations, except for periods with huge mass fluxes, when 210Pb fluxes reached a constant value. 210Pb activities decreased with increasing mass flux; then did not show clear relationship with the concentration of the major constituents of the flux. fluxes, obtained from the traps were mainly in excess of the theoretical 210Pb flux, available in the overlying water column. Since 210Pb inventories, measured on the basis of the shelf and slope bottom sediments, were also in excess in relation to the available flux. The margin, as a whole, appears as a sink for 210Pb. This boundary-scavenging process appears to be controlled completely by the mass flux of particles. Differences were observed between 210Pb fluxes in the near-bottom traps and in the underlying sediments; there can be linked to mass flux and/or morphobathymetry (the trap flux is higher than the sediment flux in the canyon, but lower on the open slope). Overall, the differences were not in excess of 50%, confirming good representation of data collected by the sediment traps. However, this finding must be taken into account when comparing organic carbon or other constituent fluxes, between the traps and the sediment.