December 8, 2025: Thesis defense by Eva Ferreira, supervised by Christophe Rabouille and Bruno Lansard.
On Monday, December 8, 2025, Eva Ferreira defended her PhD thesis about “Benthic dynamics of carbonates and acidification in two contrasting deltas: the cases of the Rhône and Mississippi Rivers.” This thesis was completed within the OCEANIS team. It led to international collaborations, notably with Martial Taillefert (Georgia Tech University) and Jordan Beckler’s teams (Florida Atlantic University), and to the publication of two scientific papers.
The work focuses on two contrasting deltaic environments subject to increasing anthropogenic and climatic pressures: the Rhône River prodelta, characterized by significant terrigenous inputs without marked hypoxia, and the Mississippi River Delta in the northern Gulf of Mexico, subject to summer hypoxia and pronounced acidification. The thesis is based on three oceanographic campaigns and eight sea expeditions. These cruises enabled the collection of samples for the analysis of porewaters, benthic fluxes, and the characterization of sediments and bottom waters in order to identify the main diagenetic processes controlling the fluxes of total alkalinity (TA) and dissolved inorganic carbon (DIC) at the water-sediment interface, as well as the occurrence of carbonate dissolution.
The results highlight strong mineralization gradients between the river mouths and the continental shelf in both systems, with TA:DIC ratios below 1, indicating a contribution of sediments to the acidification of bottom waters. Despite variable states of undersaturation, which are more pronounced in the Mississippi River Delta, no dissolution of sedimentary carbonates is observed. Winter monitoring in the Rhône prodelta also reveals biogeochemical reorganizations associated with floods, with a temporary amplification of DIC production, highlighting the high seasonal variability of these deltaic systems.
Winter monitoring of the biogeochemistry of sediments in the Rhône River prodelta in response to flood inputs : https://doi.org/10.5194/bg-21-711-2024
Article studying the dissolution of carbonates in sediments in the northern Gulf of Mexico: https://doi.org/10.1016/j.marchem.2025.104515