Observations and in-situ modeling of boreal soil carbon and associated methane emissions

• Main Author: Morel, Xavier
• Other Authors: Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), Université Paul Sabatier - Toulouse III, Bertrand Decharme, Christine Delire, Gerhard Krinner
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2018
• Subjects: Permafrost; Methane; Soil carbon; Modeling; Greenhouse gas; Boreal ecosystems; Pergélisol; Méthane; Carbone du sol; Modélisation; Gaz à effet de serre; Ecosystèmes boréaux; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; Arctic; Climate change; greenlandic; permafrost; pergélisol
• Online Access: https://theses.hal.science/tel-02484763; https://theses.hal.science/tel-02484763/document; https://theses.hal.science/tel-02484763/file/2018TOU30347d.pdf

The methane is one of the most powerful greenhouse gases in the atmosphere, with the carbon dioxyde and the water vapour. At the global scale, most of natural methane emissions come from high latitude wetlands and permafrosts. These regions accounts for a large part of terrestrial carbon stocks. In a climate change context, their future is highly uncertain, like the associated greenhouse gas emissions. Understanding the biogoechemical processes leading to methane fluxes and their interactions with surface processes is therefore important. One of the objectives of this thesis is to represent methane fluxes from these regions within the land surface model ISBA. To do so, we developped a biogeochemical model that represents explicitely gases, their production, consumption and transport within the soil column. This model is coupled with a new dynamic soil carbon model, vertically discretized, also developed during this thesis. The new biogeochemical model represents correctly methane and carbon dioxyde fluxes on three distinct arctic sites, with or without permafrost. The representation of underground biogeochemical processes is also satisfying. Nevertheless, some parameters remain uncertain and the model is very sensitive to hydrological conditions. We also measured soil carbon stocks and profiles in one of the Greenlandic studied fen. Comparing these stocks and profiles with the modelled carbon stocks shows some shortcomings of the new discretized soil carbon model : CENTURY original structure and parametrisation is not perfectly suited for high-latitudes wetlands, and the representation of carbon vertical dynamics needs improvements. Le méthane est l'un des plus puissants gaz à effets de serre présent dans l'atmosphère, avec le dioxyde de carbone et la vapeur d'eau. A l'échelle globale, la majorité des émissions naturelles de méthane proviennent des zones humides et des pergélisols de haute latitude. Ces zones sont un réservoir important de carbone et dans un contexte de changement climatique, leur devenir est ...