Nepheloid structure and hydrographic control on the Barcelona continental margin, northwestern Mediterranean

Contemporary processes controlling the off-shelf transport of sediment particles on the Barcelona continental margin were identified using CTD/transmissometer profiles during three hydrographic surveys. A well defined pattern of particulate matter distribution consisting in surface, intermediate and near-bottom nepheloid layers related with topographic and hydrographic structures was observed. Suspended sediment supplied by rivers or resuspended on the shelf is transferred to the slope mainly through the bottom nepheloid layer. A detachment of this layer is produced at the shelf break generating an intermediate nepheloid layer that transports sediment from the shelf to the slope. This transport is observed along the whole shelf break, although the maximum transference takes place through the Foix submarine canyon. On the slope, an increase of particulate matter concentration has always been recorded along the 300-500 m isobaths associated with a permanent intermediate nepheloid layer. This slope nepheloid structure is controlled by the slope density front dynamics and by the associated geostrophic current. This pattern of particulate matter distribution had not been observed before in the study area, and shows some peculiarities different from any other continental margin that has been studied. (C) 1998 Elsevier Science B.V. All rights reserved.