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Approche de la dynamique des particules dans le sillage des Kerguelen, à l'aide des traceurs géochimiques : 230Th et 231Pa

Célia Venchiarutti 1
1 GEOMAR LEGOS
LEGOS - Laboratoire d'études en Géophysique et océanographie spatiales
Abstract : 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.
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Célia Venchiarutti. Approche de la dynamique des particules dans le sillage des Kerguelen, à l'aide des traceurs géochimiques : 230Th et 231Pa. Océan, Atmosphère. Université Paul Sabatier - Toulouse III, 2007. Français. ⟨tel-00204680⟩

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