Abstract:
A general hydrographic and nephelometric survey of the NW Portuguese continental shelf and upper slope Was undertaken, under winter and spring conditions. The general circulation controls the seaward extension of the nepheloid layers. In winter, under dominant downwelling conditions, an intense bottom nepheloid layer (BNL) was
observed on the shelf due to river borne particle supply and remobilization of mid-shelf muddy sediments (depth,,;IOOm). Near the shelf-break the BNL detached to form intermediate nepheloid layers (INL). A surface nepheloid layer (SNL) appears in the surface water over the shelf and slope. In spring the SNL produced I mainly biologically is evident and separated from the BNL by clear waters, but in winter it was restricted to the
inner shelf and was due to fluvial particles. Downwelling circulation probably induces transport of shelf particles to deeper waters in the BNL. In spring, the predominant circulation was southward (upwelling), the water column was highly stratified, and dispersion of particles in the SNL was offshore.
