Recent sedimentation and mass accumulation rates based on Pb-210 along the Peru-Chile continental margin

The concentrations of the natural radionuclide Pb-210 were measured in sediment samples collected with a multicorer, boxcorer, and gravity corers along the Chilean continental margin (20-45 degreesS) in order to estimate sedimentation rate (SR) and mass accumulation rate. This database was compared with previously obtained results from central Peru (Callao). Pb-210 activities decreased exponentially with core depth and profiles showed a deepening of the Pb-210 in excess (unsupported) in the sediments from north to south (similar to6-18 cm sediment depth off Peru and northern Chile vs. 8-35 cm off central and southern Chile. An onshore-offshore decrease of surface activities was observed off central Peru whereas the reverse was true for surface activities along the Chilean margin. SRs increased from north (0.04-0.17 cm yr(-1)) to south (0.09-0.29 cm yr(-1)). Across the shelf, higher rates were observed at deeper sites, especially at those close to submarine canyons, except off central Peru, where SRs showed similar values through the slope area. Off northern Chile and central Peru, SRs seem to reflect the export of particles over the shelf and redistribution processes such as slumps and lateral transport. In contrast, SRs in central and southern Chile seem to be controlled by several additional factors that modulate the settling particles, such as onshore precipitation and river runoff. In addition, the more complex topography of the southern Chile margin allows for settling or winnowing areas. (C) 2004 Elsevier Ltd. All rights reserved.