In-situ depth profiling of particle sizes

A new in-situ particle-size profiling system is presented. It allows direct determination of particle distribution spectra in 30 size classes ranging from 0.7 to 400 μm-equivalent diameter as well as an unbiased estimation of the total particle load. This profiler includes among standard probes a particle-size analyser. This new probe uses the well-known principle of diffraction pattern analysis previously used in bench-top instruments. However, the rigorous mechanical tolerances imposed by oceanographic use required a completely new design. Its description and validation is presented as well as some oceanographic applications. This instrument presents numerous advantages in oceanographic research. Its use in different European waters has demonstrated its reliability and allowed the description of common features of the profiles, particularly the accumulation of aggregates or mucilages and, in some cases, the confinement of dinoflagellates at the pycnocline. This makes possible a new sampling strategy for toxic dinoflagellates and improvements in the study of sedimentation and flocculation processes.