Biogeochemical cycling of Fe and Mn in the Indian sector of the Soutern Ocean

• Main Author: Baudet, Corentin
• Other Authors: Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Bretagne occidentale - Brest, Hélène Planquette, Géraldine Sarthou, Eva Bucciarelli
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2023
• Subjects: Biogeochemical cycle; Iron; Manganese; Sources; Sinks; Processes; Cycle biogéochimique; Fer; Manganèse; Puits; Processus; [CHIM.OTHE]Chemical Sciences/Other; Austral; Indian; Southern Ocean; Prince Edward Islands
• Online Access: https://theses.hal.science/tel-04614538; https://theses.hal.science/tel-04614538/document; https://theses.hal.science/tel-04614538/file/These-2023-SML-Chimie_marine-BAUDET_Corentin.pdf

This thesis focuses on the study of the iron (Fe) and manganese (Mn) cycles in the Indian sector of the Southern Ocean, between the the South African coast and the Marion and Prince Edward Islands. This transect covers two zones: the subtropical zone (STZ) and the subantarctic zone (SAZ). Fe and Mn are two essential micronutrients for phytoplankton, as they are involved in many key metabolic processes. Particularly in the SAZ, Fe is considered to be a limiting element for phytoplankton growth, and Mn can sometimes be co- limiting. However, the sources, sinks and processes controlling Fe and Mn distributions remain poorly identified. The thesis reveals that atmospheric and sedimentary inputs are the dominant sources of these elements close to South Africa. The resuspension of sediments in the STZ favors the scavenging process, limiting the supply of dissolved Fe and Mn to the open ocean. Between Marion and Prince Edward Islands, biogenic particles above the shallow plateau influence the distribution of dissolved Fe and Mn and potentially promote spring phytoplankton bloom. In the SAZ, the less refractory nature of the sediments could enhance the dissolution process. Hydrothermal inputs have also been identified on the South-West Indian Ridge using a multi-element approach. Although this hydrothermal source has not been precisely localized, it generates an increase in concentrations (~ 1500m) of dissolved Fe and Mn in the surrounding waters. The potential impact of these hydrothermal inputs on the fertilization of surface waters appears to be limited, however, due to the low topography of the area. The possible importance of sources and sinks has also been examined:biological assimilation and remineralization contrai dissolved Fe distributions more in the SAZ, while these processes are masked by external sources in the STZ for dissolved iron, and over the entire transect for dissolved Mn. In conclusion, this thesis sheds light on sources, sinks and processes influencing trace métal distributions in the South-West ...