The main purpose of this work was to study the biogeochemical fate of the Rhône River particulate organic matter, and investigate the mechanisms involved in the carbon cycle of its delta. In situ microsensors measurements allowed us to perform high resolution oxygen profiles in the sediment and estimate thus the sediment recycling. It appears that the seasonal variability of the Rhône River inputs, both in quality and in quantity, impacts the benthic mineralization activity in the Rhône River delta. Nevertheless, the influence of these pulsed inputs is limited in time: deltaic sediments are a stable centre of organic carbon degradation. More than just a major mineralization area, isotopic analyses (14C and δ13C) showed that the prodelta also acts as a massive burial centre for organic particulate matter of the Rhône River. Using a stationary diagenetic numerical model, we were able to quantify these burial and degradation terms, and highlighted the importance of anoxic mineralization processes. Moreover, an important pool of suspended matter particles feeding the prodelta and originating from the adjacent continental shelf was identified: terrigeneous and marine particles, already degraded and that have encountered many deposition/resuspension cycles, dilute the riverine particles and decrease thus the lability of the material reaching the sea floor. Finally, respiration measurements in the water column underlined the impact of hydrological variations of the Rhône River that change distinctly the carbon export terms from the delta towards the continental margin.
Fate and impact of fluvial inputs on continental margins : biogeochemical and environmental importance of the recycling in the sediments of the Rhône River prodelta