Etude du cycle biogéochimique du fer : distribution et spéciation dans l’Océan Atlantique Nord (GA01) et l’Océan Austral (GIpr05) (GEOTRACES)

• Main Author: Tonnard, Manon
• 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 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), Antarctic Climate and Ecosystems CRC - Australia, Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC), Université de Bretagne occidentale - Brest, Université de Tasmanie (Australie), Géraldine Sarthou, Andrew Bowie, Hélène Planquette
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2018
• Subjects: Iron; Biogeochemical cycle; Phytoplankton growth limitation; Organic speciation; Fer; Cycle biogéochimique; Limitation de la croissance du phytoplancton; Spéciation organique du Fe; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; Austral; Southern Ocean; North Atlantic
• Online Access: https://tel.archives-ouvertes.fr/tel-02125289; https://tel.archives-ouvertes.fr/tel-02125289/document; https://tel.archives-ouvertes.fr/tel-02125289/file/These-2018-SML-Chimie_marine-TONNARD_Manon.pdf

It is now recognized that iron (Fe) availability dictates the efficiency of the global biological carbon pump such that any perturbation of Fe sources will lead to changes in the carbon cycles with consequences on both other major nutrient cycles and the climate system, controlling about 50% of the worldwide ocean primary production. However, the underlying processes themselves that affect the pathways releasing and trapping Fe, and the relative predominance of Fe sources among the different ocean basins are still poorly constrained. More importantly, the extent to which both the chemical and the physical speciation of Fe are available and accessible for marine organisms, once it enters the ocean, remains uncertain. The reactivity of Fe within the marine environment will depend on its redox and complexation state, with DFe generally considered the most bioavailable form for phytoplankton and Fe-binding organic ligands likely increasing the residence time of Fe that enables enhanced DFe concentrations way above its inorganic solubility in seawater (c.a. 10 pmol L-1).In this context and as part of the international GEOTRACES program, this thesis aims at improving our knowledge on Fe biogeochemical cycle in the ocean and its interactions with the phytoplankton community structure to better constrain the bioavailable forms of Fe. The objectives of this thesis revolve around three scientific questions: 1) What are the distributions, sources, and sinks of dissolved iron? 2) What is the link between the phytoplankton community structure and dissolved iron concentrations? 3) How the organic speciation of dissolved iron affects its concentrations and bioavailability for the phytoplankton community? These three questions were investigated through two contrasted areas: the North Atlantic Ocean (GEOVIDE, GA01 GEOTRACES voyage, PIs G. Sarthou and P. Lherminier) and the Southern Ocean (HEOBI, GIpr05 GEOTRACES voyage, PIs A. Bowie, T. Trull, Z. Chase) the former being occasionally seasonally depleted in Fe, the latter ...