My contribution to scientific research concerns the climate / biogeochemical cycles feedbacks, through studies of the temporal evolution of the atmospheric concentration of greenhouse gases (GHG), using ice cores and interstitial air in polar firn.

 

I mostly studied these feedbacks through the reconstruction of temporal trends for mixing ratios and some isotopic ratios of GHG such as methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O), ozone (O3) and some organo-halogenated compounds, but also of carbon monoxide (CO) which plays a major role on atmospheric chemistry. In another field of research, I have explored the state and dynamics of the climate system in the past, by initiating the use of global changes in atmospheric CH4 as a chronological constraint or to constrain climatic and glaciological parameters (temperature and accumulation in Antarctica, chronology of trapped gases in polar ice). Lastly, the last years have seen me investing into a new field : instrumental oceanography and process studies in the ocean through the in-situ and high resolution analysis of dissolved gases, and associated investigations of marine processes.

 

My research activity is dominated by instrumental and analytical work, including for instant the set-up and development of isotope geochemistry at LGGE in the mid 90s. In the mid 2000s, I also launched the application of new laser optical spectroscopy techniques on trace-gas analyses in ice cores.

 

I also contributed to modelling activities, with essentially a new major theme every 10 years. I started with modelling methane sources at different time scales. Then I contributed to a specific approach on the spatial distribution of wetlands. More recently I contributed to the use of a model of intermediate complexity to evaluate the role played by permafrost on the carbon cycle during the Quaternary era.

 

The main breakthroughs that one could extract from this activity can be summarized as :

• The pioneering reconstruction of the methane GHG in the atmosphere extended until the last 800,000 years, highlighting the amplitude of the recent anthropogenic impact, the strong coupling between climate and CH4 at orbital periodicities, the major role played by low latitude sources in its natural budget;

 

• The quantification of the dynamics of rapid climate events during a glaciation, revealing their impact at global scale, and with the first demonstration that they are accompanied by a bipolar see-saw, redistributing energy between the two hemispheres ;

 

• A few results at the forefront in reconstructing and interpreting isotopic ratios of GHG in firn and ice, with biogechemical conclusions of major impact : identification of the anthropogenic sources involved in the recent increase of atmospheric CH4 (carbon isotopes), a similar approach on N2O (oxygen and nitrogen isotopes), indication of a major role played by the deep ocean on the glacial-interglacial evolution of CO2 (carbon isotopes), demonstration of a large variability of biomass burning in the Southern hemisphere between 1600 and 1900 (carbon and oxygen isotopes of carbon monoxide), demonstration that tropospheric ozone increased by less than 40% since pre-industrial times (doubly substituted isotopologue of oxygen).

 

• The methodological revolution brought by OF-CEAS laser spectrometry for trace-gas analyses in ice cores and in the oceans : ERC Advanced Grant to develop the innovative probe SUBGLACIOR, first patent submission through CNRS for its oceanographic counterpart (SUBOCEAN) ; SATT and ERC Proof of Concept Grants to conceive new oceanographic instruments and to lead to their possible industrialization, application leading to a major revision of methane fluxes at the sediment-ocean interface in the Fram Straight.   

 

In terms of research management, my involvement largely increased since 2003 :

• Deputy director of LGGE (in alter ego with Michel Fily, director) and then director of the "Climate: Past, Present, Projections" (CLIPS) team followed by the "ice Core, Climate, Chemistry" (ICE3) team,
• contribution to national evaluation committees (PNEDC, National Committee recruiting and promoting CNRS researchers, ocean-atmosphere advisory committee of the National Institute for Earth Sciences and Astronomy),
• national contact within large international programmes/projects of IGBP (PAGES, AIMES, IPICS, EuroPICS) and member of evaluation Panels of the ERC.

 

From 2018 to 2022, most of my time was devoted to the position of Executive Director of the French polar institute Paul-Emile Victor (IPEV). I was also been nominated during that time as Project Manager for Polar Affairs, attached to the science directorship of CNRS.

From July 2021 to March 2025, I acted as Chairman of the Ice Memory Foundation.

In November 2022, I have been nominated Full Professor at the Swiss Federal Institute of Technology - Lausanne (EPFL) where I head the laboratory for Smart Sensors in Extreme Environments (SENSE), focusing on technologies and applications for greenhouse gas analyses in aquatic environments, in particular at the poles. I am also Academic Director of the ALPOLE consortium of EPFL on the Sion associated campus in Valais.