Spatial variability of organic matter and phosphorus cycling in Rhône River prodelta sediments (NW Mediterranean Sea, France): a data-model approach

The Mediterranean Sea (MS) is a large oligotrophic sea. Its productivity may be sensitive to riverine nutrient inputs. Understanding its productivity involves quantifying phosphorus (P) river supply which is crucial for calculating P mass balances in the anthropogenically disturbed sea. Yet the precise role of the deltaic filter is not known, especially concerning the  differential trapping/recycling of nutrients in deltaic sediments. A benthic dataset from the Rhône River prodelta was coupled to an early diagenetic model, including the benthic P cycle. The dataset comprised  porewater oxygen, nitrate, sulfate, dissolved inorganic carbon, ammonium, dissolved reduced and total iron, dissolved inorganic phosphorus (DIP) and solid data (organic carbon, Fe-bound P, Ca-bound P and organic P) for 9 stations from the Rhône River prodelta. The model results indicated that the intensity of biogeochemical processes occurring near the sediment–water interface decreased from the river mouth to the adjacent continental shelf. This decrease occurred according to OC fluxes to the seafloor, sedimentation rates and integrated rates of OC mineralization (from 160 mmol C m-2 d-1 near the mouth to 10 mmol m-2 d-1 on the shelf). The organic P mineralization was intense, especially near the river mouth (1196 µmol m-2 d-1), and its contribution to DIP release was large (> 90%). Fe-bound P had a key role in promoting Ca-bound P precipitation in anoxic sediments. These sediments played an important role as a source of regenerated DIP.A significant part of DIP was recycled to the overlying waters (72-94%), representing 25% of the riverine discharge input of DIP. While 6-28% of produced DIP was buried as Ca-bound P, which represented 3-6% of the riverine inputs. Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.