Approach of the particle dynamics in the wake of Kerguelen, using geochemical tracers: 230Th and 231Pa

• Main Author: Venchiarutti, Célia
• Other Authors: GEOMAR LEGOS, Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Université Paul Sabatier - Toulouse III, Catherine JEANDEL
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2007
• Subjects: KEOPS; thorium; protactinium; boundary scavenging; Southern Ocean; Isotopic tracers; particles; settling velocities; Océan Austral; traceurs isotopiques; particules; vitesses de chute/ KEOPS; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Austral; Kerguelen; Le Plateau
• Online Access: https://tel.archives-ouvertes.fr/tel-00204680; https://tel.archives-ouvertes.fr/tel-00204680/document; https://tel.archives-ouvertes.fr/tel-00204680/file/TheseComplete_Venchiarutti_version_80108.pdf

During the Kerguelen Ocean and Plateau compared Study Project, particle dynamics (settling velocities, residence times) and dissolved/particle exchanges (boundary scavenging) were investigated to understand the mechanisms responsible for the natural iron fertilisation observed over the Kerguelen plateau. This work proposes to use two oceanic radionuclides 230Th and 231Pa - both decay products of Uranium and submitted to particle removal - as particle dynamic tracers. More than a hundred 230Th and 231Pa concentrations in dissolved and particulate phases were obtained, resulting in 10 characteristic and relevant oceanic profiles. The plateau, in spite of its high C export revealed low 230Th derived particle settling velocities (S= 500 m/y) whereas the off-plateau stations, considered as HNLC area, exhibit higher settling speeds (S= 800 m/y). This unexpected result raises a question on the relevance of 230Th reversible scavenging model applied. The influence of lateral advection on the plateau was highlighted by a "2D" reversible scavenging model which seems more appropriate to represent the coast-open ocean system. On the plateau, high 231Pa dissolved concentrations suggest the release of 231Pa in solution, likely linked to the re-mineralisation of opal rich aggregates (efficient Pa scavenger). On the eastern escarpment of the plateau, evidence of an intensive boundary scavenging has been shown in the deep waters by conspicuous depletions in both dissolved 230Th and 231Pa concentrations with a concomitant enrichment in the particles, due to the presence of nepheloid layers or re-suspension from the shelf or bottom opal rich sediment. Lors du projet Kerguelen Ocean and Plateau compared Study (KEOPS), la dynamique des particules (vitesses de chute, temps de résidence) et les interactions entre dissous et particules (" boundary scavenging ") ont été étudiées afin de mieux comprendre les mécanismes responsables de la fertilisation naturelle en fer observée sur le plateau des Kerguelen. Notre étude utilise deux ...