Etude des émissions de fluide et de gaz dans un contexte d’éruption sous-marine au large de l’Ile de Mayotte : impact géochimique sur la colonne d’eau

• Main Author: Mastin, Manon
• Other Authors: Geo-Ocean (GEO-OCEAN), Université de Bretagne Sud (UBS)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Université de Bretagne occidentale - Brest, Olivier Rouxel, Emmanuel Rinnert, Cécile Cathalot
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2023
• Subjects: Geochemistry; Submarine volcanism; Fani Maoré; Dissolved gases; Liquid CO2; Water column; Géochimie; Volcanisme sous-marin; Gaz dissous; CO2 liquide; Colonne d’eau; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Indian; Ocean acidification
• Online Access: https://theses.hal.science/tel-04394229; https://theses.hal.science/tel-04394229/document; https://theses.hal.science/tel-04394229/file/These-2023-SML-Geosciences_marines-MASTIN_Manon.pdf

Submarine volcanism contributes significant fluxes of chemicals (e.g. He, CO2, CH4, H2, Fe2+, Mn2+) in the ocean. However, the geochemical processes behind these emissions and the impact of these discharges on the water column geochemistry are poorly documented. In this PhD thesis, we took advantage of the Fani Maoré newly born submarine volcano whose activity started in 2018-2019 (Mayotte Island, Comoros Archipelago, Indian Ocean). This exceptional and unique setting offers the opportunity to study the water column geochemistry during the eruption and formation of a new volcanic edifice, and after the eruptive event (i.e. during lava flows installation and hydrothermal circulation initiation). In particular, we investigate the impact of elevated levels of CO2 – major greenhouse gas involved in climate change and associated ocean acidification – on the water column geochemistry. We find evidence of the relationship between the degree of eruptive activity (i.e. ongoing eruption, lava flow installation) and the footprint of fluid and gas emissions within the water column. The volcanic activity also influences the carbonate system although a return toward local background levels was observed a year after the main eruptive event. Continuous discharge of liquid CO2 at venting sites are responsible of significant acidification, increase in alkalinity and in dissolved inorganic carbon. This impact on the water column depends on seafloor morphology and local hydrodynamics. Overall, this work is a step toward a better understanding of the impact of submarine volcanism on geochemical processes taking place within the water column and more generally on the ocean chemistry. Le volcanisme sous-marin émet des flux significatifs d’éléments chimiques (ex. He, CO2, CH4, H2, Fe2+, Mn2+) dans l'océan. Cependant, les processus géochimiques à l'origine de ces émissions et l'impact de ces rejets sur la géochimie de la colonne d'eau sont peu connus. Dans cette thèse, nous avons étudié le nouveau volcan sous-marin Fani Maoré, dont ...