Pb-210 sedimentation rates from the Northwestern Mediterranean margin
Résumé
A total of 83 cores were collected in the Gulf of Lions continental margins and analysed for Pb-210(xs) (excess Pb-210) in order to understand sedimentation patterns. Apparent sedimentation rates (ASR) range from 0.65 cm year(-1) in the vicinity of the Rhone River mouth to 0.01 cm year(-1) in the deep basin. Except for the prodelta, area, rates decrease with depth linearly with the water depth. On the slope, ASR do not differ between canyons and open slope, except for the western area where the rates are slightly higher in the Lacaze-Duthiers canyon compared to its adjacent, open slope. In the canyon and open slope areas, mass accumulation rates determined from Pb-210(xs) profiles (0.10 and 0.08 g cm(-2) year(-1), respectively) are in good agreement with particulate fluxes calculated from 5 years of near-bottom sediment trap data, even when the trap particle fluxes and the apparent accumulation rates are overestimated in response to resuspension and bioturbation effects. However, differences in sediment trap data, between west and east portion of the slope, are not observed in the sedimentation rates calculated with Pb-210(xs). The outer shelf area may have an important role in trapping sediment but it is not sufficiently documented. Sediment surface mixed layer depths decrease with water depth, with a mean value for the whole margin of 8 +/- 6 cm. Pb-210(xs) inventories in the sediment are systematically higher than the net Pb-210 export flux estimated from the above water column. Over the margin, the ratio between accumulated Pb-210 and available Pb-210 is about 3, suggesting boundary scavenging effects and advective transport