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Etude des Particules Exopolymériques Transparentes (TEP) en milieu marin. Dynamique et rôle dans le cycle du carbone

Abstract : The study of Transparent Exopolymeric Particles (TEP) has been a field of increasing interest over the past ten years. Their main source is exsudation of polysaccharides by phytoplankton and bacteria. These particles, which are formed abiotically, essentially by coagulation of colloidal organic matter, are strongly involved in marine biogeochemical processes. Two techniques for determining the presence of TEP were compared (“Filter-Transfer-Freeze” and “Frosted White Slides”) and their limits and advantages were evaluated in order to establish an optimal procedure. In the following work, the second method was preferred for its better results in terms of precision and accuracy. A study of the seasonal variations of TEP in the North-western Mediterranean from February 1999 to February 2000 was carried out at two sites, one being at the coast and the other offshore (DYFAMED-JGOFS program). The TEP remained very abundant during the whole year (from 2.104 to 2.105 TEP ml-1) in the euphotic zone. Their dynamics tended to reflect the trophic status of the ecosystem rather than the regional differences. Generally, an increase of the TEP pool was observed after the spring bloom, persisting during the summer period. The present in situ study also revealed the importance of this pool of matter as a stock of organic carbon (from 0.6 to 20.5 µmol.C.l-1; up to 15% of total organic carbon). Furthermore, these particles have a C/N molar ratio which is significantly greater than the Redfield ratio (C/N = 21 in average). The formation of TEP would therefore have a major role in the transfer of carbon when over-consumption of dissolved inorganic carbon (DIC) by phytoplankton during oligotrophic conditions takes place. TEP consequently represent an important component in the carbon cycle by trapping organic carbon in a particulate form. The effect of the trophic regime associated to different degrees of turbulence on the dynamics of TEP has been monitored in controlled conditions, under the European project NTAP (Nutrient dynamics mediated through Turbulence And Plankton interactions). This showed that strong turbulence (1.10-4cm2s-3) enhances the persistence of this pool at the surface by encouraging the aggregation of particles. It is equally favourable towards bacterial colonisation of TEP. Hence, the hydrodynamics of the ecosystem should be able to influence the formation of TEP as well as the outcome of this pool of matter (accumulation and/or sedimentation). Transmission electronic microscopy coupled to an X-ray micro-analysis was applied to determine the elementary composition (C, N, P, Mg, Ca, Fe, Mn) of TEP as a function of the trophic conditions. Results confirmed the importance of these particles in terms of carbon as well as their role in the over-consumption of DIC when the environment is nitrogen-deficient. Furthermore, TEP are able to adsorb iron and manganese (up to 1.7 nM Mn and 18.7 nM Fe in a Norwegian fjord), thus pointing to their role in the biogeochemical cycle of trace elements.
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https://tel.archives-ouvertes.fr/tel-00003711
Contributor : Sophie Beauvais <>
Submitted on : Wednesday, November 5, 2003 - 3:39:12 PM
Last modification on : Wednesday, December 9, 2020 - 3:05:26 PM
Long-term archiving on: : Friday, April 2, 2010 - 7:18:50 PM

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  • HAL Id : tel-00003711, version 1

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Sophie Beauvais. Etude des Particules Exopolymériques Transparentes (TEP) en milieu marin. Dynamique et rôle dans le cycle du carbone. Autre. Université Pierre et Marie Curie - Paris VI, 2003. Français. ⟨tel-00003711⟩

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