CONTINENTAL/MARINE RATIO CHANGES IN SUSPENDED AND SETTLED MATTER ACROSS A MACROTIDAL ESTUARY (THE SEINE ESTUARY, NORTHWESTERN FRANCE)

Suspended matter movements in the macrotidal Seine estuary (France) are mainly controlled by tidal currents. During high river spates, suspended matter is carried out of the estuary into the English Channel. A large part of the estuarine suspended matter comes from continental inputs. Throughout the year, suspended matter is trapped in the Turbidity Maximum Zone and on the estuarine tidal flats. Marine particles which are concentrated in the Turbidity Maximum Zone can be transported upstream into fresh water conditions. Physical and chemical measurements, as well as grain size analysis associated with scanning electron microscopy techniques, are used to study the characteristics of silty sediments and suspended matter. In the Turbidity Maximum Zone of the Seine estuary, particulate tracers, such as diatoms, indicate a continental/marine ratio more than 90% in the suspended matter. These results are similar with those from radiotracers. Sedimentary analyses on fine deposits from the estuarine tidal flats show close similarities with suspended matter coming from the Turbidity Maximum Zone. The sedimentological processes of the Seine estuary are compared with those in some other estuaries.