Use of the Underwater Video Profiler for the study of aggregate dynamics in the North Mediterranean

The Underwater Video Profiler is a vertically deployed survey system designed for the quantification of particles >280 mu m and of large zooplankton in the 0-1000 m water column. Light reflected by undisturbed target objects forms a dark-field image, which is recorded at 25 Hz frequency. The recorded images are automatically digitized and analysed. The results are expressed as abundance or size distributions and they can be converted to volume or mass units. The system can be configured as a multi-instrument array and can simultaneously acquire biological and physical data. From May 1994 to April 1995 a monthly survey was performed across a frontal structure associated to the North Ligurian geostrophic current. In winter and spring 1995 the front, as well as the offshore dispersion limit of particles, were located near to the coast. In contrast, during autumn 1994, its position was open sea and the terrestrial matter was dispersed far from the coast. The continuous presence of intermediate nepheloid layers along the continental slope indicates that different processes may supply and transport the particulate matter to deeper layers, from where it can be diffused into the basin. (C) 2000 Academic Press.