Atelier national sur les nuages polaires

24/06/2025 09:00

SIRTA / ICEO : Journée Scientifique 2025

24/06/2025 09:00

Evénement de clôture projet FAIR-EASE

12/06/2025 09:00

Laser-based mass spectrometry in the planetary sciences: convergence of emerging priorities and enabling technologies

17/06/2025 11:30

Séminaire du LATMOS.

Big Data Assimilation Revolutionizing Numerical Weather Prediction Using Fugaku

13/06/2025 14:00

Séminaire du LMD.

Simulated climatologies of Northern Hemisphere blocking and storm tracks in AGCMs

12/06/2025 14:30

Séminaire du LMD à l’ENS.

De la distribution de la matière organique dans le système solaire

12/05/2025 14:00

La présence de matière organique est une condition nécessaire à l’habitabilité des corps du système solaire. Comprendre sa distribution, et par là-même ses sources et ses puits, est l’enquête que je mène. Cette enquête pourrait in fine mener à la détection de biosignatures. Dans cette soutenance je décris mes travaux passés qui ont abouti à la première détection de molécules organiques sur Mars. Pour cela, je travaille autant à l’analyse de données in situ (rover Curiosity) qu’à des analyses en laboratoire sur des échantillons simples ou complexes. La forme initiale des molécules détectées sur Mars commence à être élucidée, mais leur origine est inconnue : apport météoritique ou formation sur Mars par des sources atmosphériques, hydrothermales ou biologiques.

Si de nombreux exobiologistes ont leurs yeux rivés vers Mars et que de nombreuses missions continuent à étudier la planète rouge, aujourd’hui, Jupiter et Saturne sont sous le feu des projecteurs : leurs satellites glacés comme Europe, Encelade ou Titan ont un potentiel qui ne cesse de s’accroître quant à leur possibilité d’abriter des formes de vie. La mission Dragonfly explorera des environnements variés de Titan dès 2034 et je suis responsable scientifique de la fourniture hardware française à cette mission. De cette expertise, nous préparons des prochaines missions d’exploration des mondes-océans, Europe, Encelade. À l’instar des études martiennes, je recherche et analyse des environnements terrestres analogues pour préparer la science et la technique des futures missions d’exploration de l’habitabilité de ces satellites glacés.

 

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Mots clés : molécules, biosignatures, Mars, mondes-océans, chimie analytique, instrumentation

The Antarctic climate from an atmospheric point of view: modelling and water isotopes to improve reconstructions and projections

12/05/2025 14:00

The large Antarctic ice sheet is strongly connected to the Earth climate through the atmospheric circulation and water cycle. My research aims to better understand and model the processes involved in this water cycle, with two main areas of application: (i) improving reconstructions based on the isotopic signal of annually resolved firn cores and (ii) improving climate projections for the Antarctic ice sheet, in particular its contribution to sea level.

Understanding the climatic drivers of the water isotope signal measured in high-resolution firn cores requires a modelling chain comprising large-scale atmospheric water transport, air-snow exchanges and in-snow post-deposition processes. We recently leveraged newly deployed isotopic records in surface snow and water vapour in Antarctica to evaluate the isotope-enabled global atmospheric model LMDZiso. Then we used process decomposition to understand the origin of vapour isotopic variability in the model. Ongoing work aims at improving isotopic processes in snow and during air-snow exchanges. This is a fundamental step towards the use of water isotopes to constrain physical processes. It will also allow going to paleoclimate data assimilation with reduced uncertainties in the modelling chain.

Modelling the future of the Antarctic climate, including its surface mass balance, requires representing correctly both the large-scale circulation and the polar-specific processes at play. I designed specific metrics to evaluate the large-scale circulation of CMIP models in polar regions. I also developed diagnostics for evaluating the snow accumulation over the ice sheet, which I used to analyse and improve the estimation of the Antarctic surface mass balance. Then we focused on the improvement of polar processes in atmospheric models related to snow and boundary layer (albedo, densification, liquid water content, turbulence). Finally, we developed momentum budget decomposition to quantify the drivers of Antarctic surface winds.

I am pursuing the improvement of polar physics in the atmospheric model of IPSL, ICOLMDZiso, aiming at an integrated framework of the ocean-to-snow water cycle including water isotopes and coupling with ice sheet models.

Carbon cycle on fire - New insights in the carbon cycle of terrestrial ecosystems

11/04/2025 14:00

This document summaries my research for the past 18 years at the university of Zurich and the Ecole normale supérieure. It is based on three main concepts: a scientific view on the persistence of the organic matter in the ecosystems, a holistic approach on how to study plant-soil systems, and a general desire to study such complex systems with transdisciplinarity. In a nutshell, my main research questions are “how much” carbon is there is the terrestrial ecosystems, and “how fast” they transfer from one compartment to another. The main focusses of my work are the pyrogenic carbon and the root-derived carbon in the terrestrial ecosystems. The pyrogenic carbon is the remaining organic fraction of biomass after exposed to heat and fire. On this topic, I was particularly interested in the method to describe it quantitatively and qualitatively, its amount in the ecosystems, at local and global scales, as well as the mechanisms describing its distribution. I also worked on a nature based solution related to this pyrogenic carbon, namely the biochar. Regarding the plant-soil systems and the focus on root-derived carbon, I am interested in how this carbon can be studied from different time and space perspectives, with a focus on the quantity of carbon that flows through the roots and the rhizosphere during the life of the plant, and during its decomposition later on. During these studies, I came across the observation that the effect of roots on the native soil organic matter may be as important as the root-derived carbon itself. This work is globally a playdoyer for experimental science, associated to other disciplines, to study ecosystem complexity.