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Etude de la dissolution de la silice biogénique des agrégats : Utilisation dans la reconstruction des flux de sédimentation de la silice biogénique et du carbone dans la colonne d'eau

Abstract : Diatoms are key species that strongly participate to primary production and to carbon export out of the surface layer. During this PhD, the role of diatoms and the impact of aggregation on the biological pump were investigated using direct measurement of bSiO2 dissolution rates in aggregates and freely suspended diatoms during laboratory experiments and modelling. Dissolution experiments determined that bSiO2 dissolution rate constants of aggregated cells are 2-3 times lower than that of freely suspended diatoms (Moriceau et al. 2007a). The dissolution model applied to experimental data from dissolution experiment undertook with diatom aggregate showed that both bSiO2 dissolution and silicic acid (dSi) accumulation outside the aggregate were low (Moriceau et al. 2007c). (1) The decrease of the bSiO2 dissolution rate constant was attributed to the strong dSi concentrations measured into aggregates and to the higher viability of aggregated cells. (2) dSi was adsorbed on the aggregate matrix, which results in lower dSi accumulation rate in the external medium surrounding aggregate.
Experimental results were then combined with in situ measurements of bSiO2 fluxes in eight areas of the ocean, into a simple model that reconstruct bSiO2 fluxes in the water column. This model allows to calculate the repartition of the BSiO2 between large particles and freely suspended cells and to better understand particles dynamic. The BSiO2 fluxes reconstructed using the model, were then associated with a relation between Si/C ratios and water column depth to determine the real importance of diatoms in the biological pump of carbon. We then calculated the carbon fluxes at the maximum depth of the mixing layer. The use of the Si fluxes as a proxy of the carbon fluxes allow to ignore difficulties due to the complexity of the carbon chemistry. The role of diatoms in the export and transfer of carbon strongly depend on the way used to calculate the export out of the surface layer.
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https://tel.archives-ouvertes.fr/tel-00353481
Contributor : Brivaela Moriceau <>
Submitted on : Thursday, January 15, 2009 - 3:56:24 PM
Last modification on : Wednesday, October 14, 2020 - 3:52:16 AM
Long-term archiving on: : Tuesday, June 8, 2010 - 6:13:40 PM

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  • HAL Id : tel-00353481, version 1

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Brivaëla Moriceau. Etude de la dissolution de la silice biogénique des agrégats : Utilisation dans la reconstruction des flux de sédimentation de la silice biogénique et du carbone dans la colonne d'eau. Planète et Univers [physics]. Université de Bretagne occidentale - Brest, 2005. Français. ⟨tel-00353481⟩

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