MODELING OF THE SEDIMENTATION OF MARINE PARTICLES IN LAMINAR-FLOW - APPLICATION TO THE CONTINENTAL-MARGIN

In the present paper we propose an initial stage of modeling of the sedimentation of marine particles in the water-column, excluding the turbulence and the surficial water layer from 0 to 100 m. This marine sedimentation depends on several parameters: the mass concentration of particles, their density and diameters, the water temperature and salinity, the currents, etc... These parameters vary with depth and time. The model that we have developped related the flux to the different parameters; it allows to determine which among them have a prevailing influence, and to calculate some parameters whose direct measurement is difficult, provided the other parameters are well known. In order to compare the general tendences foreseen by the model and those revealed by experiment, we use experimental data obtained in the southwestern margin of the Gulf of Lions in the Northwestern Mediterranean in the framework of the ECOMARGE programme (France-JGOFS). This comparison shows that our model gives a satisfactory description of those tendences. The calculations revealed the prevailing influence of the current speed and its inclination on the particle flux in the water column. It should be noted that even an extremely slight inclination of the current modifies that flux considerably. This parameter is seldom taken into consideration and in itself it can explain the sedimentation of fine particles which are located optically in the form of nepheloids. These particles, dominanthly mineral, are found in abundance in the traps, at least in the context of continental margins. It is sure that the use of a new generation of current meters and optical instruments will cause an evolution of our hypotheses on marine sedimentation.