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 C TD/transmissometer profiles during three hydrographic surveys. A well defined pattern of particulate matter distribution consisting in surfa ce, intermediate and near-bottom nepheloid layers related with topogra phic and hydrographic structures was observed. Suspended sediment supp lied 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 l ayer that transports sediment from the shelf to the slope. This transp ort is observed along the whole shelf break, although the maximum tran sference takes place through the Foix submarine canyon. On the slope, an increase of particulate matter concentration has always been record ed along the 300-500 m isobaths associated with a permanent intermedia te nepheloid layer. This slope nepheloid structure is controlled by th e slope density front dynamics and by the associated geostrophic curre nt. This pattern of particulate matter distribution had not been obser ved before in the study area, and shows some peculiarities different f rom any other continental margin that has been studied. (C) 1998 Elsev ier Science B.V. All rights reserved.