My research contribution concerns climate/biogeochemical cycle feedbacks, via the study of the evolution of the atmospheric composition of greenhouse gases (GHGs) using ice cores and the interstitial air of the polar snowpack, but also via the study of GHGs in aquatic environments (oceans, lakes).
I have been able to reconstruct temporal trends in the mixing ratio and some isotopic ratios of the GHGs methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O), ozone (O3) and some organo-halogen compounds, but also of carbon monoxide (CO) which plays an essential role in atmospheric chemistry. My focal points have been both the Quaternary era and the industrial period. In another field of study, I have explored the past state and dynamics of the climate system by estimating the evolution of past temperatures and accumulations in Antarctica or by assessing the phase relationships between polar climate and GHG evolution. In recent years, I have been involved in the field of aquatic instrumentation and the study of biogeochemical processes in oceanic or lacustrine environments through in-situ and high-resolution analysis of dissolved gases.
The most important advances that can be retained from this work can be summarised as follows
- The pioneering reconstruction of GHGs in the atmosphere extended to the last 800,000 years, demonstrating the importance of the recent anthropogenic impact, the strong coupling between climate and CH4 at orbital periodicity, and the major role of low-latitude sources in its natural balance;
- The quantification of the dynamics of rapid climate events during an ice age, including the identification of their global extent, and the first demonstration that they involve a bipolar energy shift;
- Firsts’ in the study of GHG and CO isotope ratios in nevé and ice, leading to important biogeochemical conclusions: Identification of anthropogenic sources responsible for the recent increase in CH4 (carbon isotope) and N2O (oxygen and nitrogen isotope); Evidence of a major role of the deep ocean in the glacial-interglacial evolution of CO2 (carbon isotope); revealing a temporal modulation of biomass fires in the Southern Hemisphere by a factor of two between 1600 and 1900 (carbon and oxygen isotope of CO); demonstrating that ozone in the troposphere has increased by less than 40% since the pre-industrial period (a double-substituted isotope of oxygen).
- The methodological revolution brought by the application of OF-CEAS laser spectrometry to the analysis of gases in ice and in oceans and lakes: ERC Advanced Grant project and the innovative in-situ probe SUBGLACIOR, filing of a CNRS patent for the oceanographic derivative of this probe (SUBOCEAN); SATT and ERC Proof of Concept projects to design other oceanographic instruments and progress towards their industrialization; application leading to a major revision of methane fluxes at the sediment-ocean interface in the Fram Strait.
Most of my time from 2018 to 2022 was spent as Director of the French Polar Institute Paul-Emile Victor (IPEV), in charge of selecting and then operationally supporting French research projects in the polar regions. I was also in charge of polar affairs at the CNRS’s Directorate General for Science.
Since July 2021, I have been President of the Ice Memory Foundation, which aims to create an international sanctuary of glacier samples condemned to disappear due to climate change, stored in Antarctica for future generations of researchers.