My contribution to scientific research concerns the climate / biogeochemical cycles feedbacks, through studies of the temporal evolution of the atmospheric composition, mainly in terms of trace gases having a radiative impact, using ice cores and interstitial air in polar firn.
I mostly worked on the reconstruction and interpretation of temporal trends for mixing ratios and some isotopic ratios of greenhouse gases, such as methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O) and some organo-halogenated compounds. But also carbon monoxide (CO) which plays a major role on atmospheric chemistry. In another field of research, I have initiated the use of global changes in atmospheric CH4 as a chronological constraints on the dynamics of past climate, or to constrain glacio-climatic parameters (temperature, accumulation, gas age-ice age difference).
My research activity is dominated by instrumental and analytical work, including for instant the set-up and development of isotope geochemistry at LGGE. About 10 years ago, 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 different times.
The main breakthroughs that one could extract from this activity are in my opinion :
- Reconstruction of the detailed temporal evolution of the atmospheric methane mixing ratio, progressively 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;
- Major chronological constraints on the dynamics of rapid climate events during the last glaciation, revealing their impact at global scale, and with the 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 trace gases in firn and ice, with biogechemical conclusions of major impact : caracterization of the anthropogenic sources involved in the recent increase of atmospheric CH4 through carbon isotopes, a similar approach on N2O using oxygen and nitrogen isotopes, indication of a major role played by the deep ocean on the glacial-interglacial evolution of CO2, thanks to its carbon isotopes, demonstration of a large variability of biomass burning in the Southern hemisphere, using carbon and oxygen isotopes in carbon monoxide.
- The revolution brought by OF-CEAS laser spectrometry for trace-gas analyses in ice cores, but also now for analyzing dissolved gases in the oceans : ERC Advanced Grant to develop the innovative probe SUBGLACIOR, leading in particular to my 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.
In terms of research management, my involvement largely increased since 2003 (making up to ~50% of my work time) :
- 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 evaluating 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).
Most of my current research time is devoted to the ERC project ICE&LASERS that I lead since 2012.