Transfer mechanisms and biogeochemical implications in the bottom nepheloid layer. A case study of the coastal zone off the Rhone River (France)

Particles supplied to the coastal zone are involved in numerous biogeochemical processes that rapidly modify particulate composition. The Bottom Nepheloid Layer (BNL) thus plays a significant role on the budget of elements transferred to the coastal zone. Although it should not be ignored in flux studies, little is known about the quantity and the quality of particles transported within it, mainly due to sampling difficulties. From field experiments in the coastal zone off the Rhone River, the physical mechanisms occurring within the BNL were delineated. Its temporal variability was then examined, regarding the influence of wind, river discharge and current velocity, in order to investigate the temporal scales that control the BNL's character and the processes occurring within it. In the BNL off the Rhone, particulate transfer can be as important, quantitatively, as in the river plume, and larger by far than within the water column.