Particulate matter from the bottom nepheloid layer, off the Rhone river mouth was sampled with a newly-designed frame code-named SYMPHY. Several spreading phases of the Rhodanian suspensions on the continental shelf were evidenced by currentmeter records, particulate matter analyses, CTD and nephelometric measurements. These data permitted the study of the mechanisms which control the aging of the suspensions during their transfer to a sea with very small amplitude tides. The bottom nepheloid layer can be defined as a vertical concentration gradient resulting from an equilibrium between the horizontal (Rhodanian inputs) and the vertical (surface nepheloid layer) components of the particulate flux. The variability of this equilibrium, controlled by hydrodynamic fluctuations, involves different residence times and permits modifications of the nature of suspensions by biogeochemical processes.