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Étude des relations bio-optiques dans l’océan global et du fonctionnement biogéochimique des maxima de subsurface de chlorophylle en Méditerranée à partir des mesures des flotteurs profileurs BGC-Argo

Abstract : The main objective of this thesis is to improve our understanding of the spatio-temporal and vertical variability of phytoplankton biomass in the open ocean. First, we investigated the variability of the relationship between the particulate backscattering coefficient (bbp), a bio-optical proxy of the particulate organic carbon, and the chlorophyll a concentration (Chla) at a global scale. In subpolar regimes, concomitant changes in Chla and bbp correspond to variations in phytoplankton biomass. In contrast, in subtropical regimes, a decoupling between the two variables was attributed to photoacclimation processes or a change in the relative abundance of non-algal particles to the particulate assemblage. The Mediterranean Sea stands as an intermediate regime between these two end-members. Next, we analysed the seasonal and regional dynamics of subsurface Chla maxima (SCMs) in the Mediterranean basin by developing a classification of the vertical profiles of Chla and bbp. In the Eastern Mediterranean, SCMs corresponded to an increase in the intracellular Chla induced by photoacclimation of phytoplankton cells. However, in the Western basin of the Mediterranean Sea SCMs corresponded to an actual increase in carbon biomass at depth (SBMs). Lastly, we investigated the potentially significant contribution of SCMs to carbon production, by quantifying the gross community production in the subsurface layer. A method based on the diurnal cycle of bio-optical properties was used in order to estimate production in two distinct regions of the Mediterranean Sea during the oligotrophic season. Our study revealed that SCMs might contribute over 40% of the depth-integrated production in some areas, thereby suggesting the potentially important biogeochemical role of SCMs.
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https://tel.archives-ouvertes.fr/tel-02926277
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Submitted on : Monday, August 31, 2020 - 3:32:06 PM
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Marie Barbieux. Étude des relations bio-optiques dans l’océan global et du fonctionnement biogéochimique des maxima de subsurface de chlorophylle en Méditerranée à partir des mesures des flotteurs profileurs BGC-Argo. Océanographie. Sorbonne Université, 2019. Français. ⟨NNT : 2019SORUS490⟩. ⟨tel-02926277⟩

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