Distribution and transport processes of marine particulate matter off Cape Blanc (NW-Africa): results from vertical camera profiles

Abstract. In this study, we present vertical particle profiles acquired with the deep-sea camera system ParCa. The profiles were obtained during three campaigns in the spring seasons of 2001–2003 off NW-Africa (Cape Blanc). The camera profiles showed interannual and spatial variabilities regarding the particle concentrations in the ocean surface which were related to changes in the Chl-a biomass concentration. Although particle concentrations varied, all profiles showed rather similar distribution patterns. They were characterised by a subsurface particle maximum layer, around 200 m at stations close to the coast and around 400 m at stations further offshore. We argue, that at least a portion of the material seen in the subsurface maximum originates from the coast, and was laterally advected towards the open ocean by filament activity. Apart from this offshore transport, increased concentrations of particulate matter above the seafloor suggest a downslope transport of particulate matter near the seafloor. Both hypothesis were tested with model computations, described in a companion paper. A special sedimentation event was observed during a field campaign in 2001. The particle abundance patterns and the size distributions most likely reflect a sinking event, where particulate matter is transferred on very short time scales from the surface to the seafloor. We assume, that the fast sinking particle cloud preferably scavenges the more abundant small particles, resulting in larger particles sizes above and within the sinking cloud.