The fate of biogeochemical elements in Mediterranean sea at the air-sea interface in the context of climate change

• Main Author: Louis, Justine
• Other Authors: Laboratoire d'océanographie de Villefranche (LOV), Observatoire océanologique de Villefranche-sur-mer (OOVM), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris VI, Cécile Guieu
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2015
• Subjects: Ocean acidification; Saharan desert; Bioavailability of atmospheric nutrients; Acidification de l'océan; Évènement saharien; Agrégation; Dissolution; Pompe biologique; Pompe lithogénique; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography
• Online Access: https://theses.hal.science/tel-01316537; https://theses.hal.science/tel-01316537/document; https://theses.hal.science/tel-01316537/file/2015PA066527.pdf

The objective of this thesis was to assess the biogeochemical effect of two forcings: the ocean acidification and the dust deposition. Firstly, we showed that in the Low Nutrient Low Chlorophyll (LNLC) area the effect of the ocean acidification on the marine cycle of nitrogen (N), phosphorus (P) and iron (Fe) will be likely negligible. The pH decrease of the surface waters depleted in N and P would not affect the speciation of these elements, and the absence of effect on the composition of the plankton community would not lead to a shift in the dynamic of inorganic nutrients. Secondly, the experiments performed during this thesis allowed a better parametrization of the post-depositional processes of atmospheric nutrients in the surface seawater after a Saharan event. The exchanges dissolved/particulate occurred in the short timescale. They were controlled by both the particles dynamic and the nature of the dissolved organic matter (DOM) that can aggregate with the lithogenic particles. Under ocean acidification conditions, while the dissolution of anthropogenic elements adsorbed onto dust, such as the inorganic nitrogen, will not be affected, the dissolution of the crustal elements (P and Fe) could be higher and faster according the formation of organic-dust aggregates. The major role of the aggregation process on the availability of atmospheric nutrients was highlighted by the rapid and large abiotic formation of transparent exopolymeric particles (TEP) following the dust deposition to the surface waters. L'objectif de cette thèse a été d'évaluer l'effet biogéochimique de deux forçages : l'acidification de l'océan et les dépôts de poussières sahariennes. Dans un premier temps, nous avons montré que dans une région dite Low Nutrient Low Chlorophyll (LNLC) l'effet de l'acidification de l'océan sur les cycles marins de l'azote (N), du phosphore (P) et du fer (Fe) sera surement négligeable. L'acidification des eaux de surface appauvries en N et P n'affecterait pas la spéciation de ces éléments, et la composition ...