Climate forcing and the carbon cycle

The study of the evolution of the greenhouse effect and the mechanisms regulating the carbon cycle, on all time scales, is one of the central themes of the Climate team. We are studying solar and volcanic climate forcings over the last millennium, based on records of 10Be concentration in Antarctic ice cores. Our reconstructions of these forcings contributed to the comparison of climate models (CMIP6 and PMIP4) in the latest IPCC report. To complement and better understand the information provided by 10Be, we have developed the measurement of 36Cl in polar ice, another climate indicator. Their isotopic ratio is also an important dating tool for ice cores. These approaches are being developed as part of several international projects (H2020 Beyond EPICA-Oldest Ice, 2019-2026, ANR ToBE 2023-2027, both led at CEREGE by Mélanie Baroni). Another aspect of this work is based on the measurement of 14C at annual resolution in subfossil wood covering the last deglaciation (ANR MARCARA, 2021-2025, continuation of the ANR CARBOTRYDH project, led by Edouard Bard). Our records from wood from the French Alps are being compared with similar results from the southern hemisphere (New Zealand and Tasmania) and with cosmonucleide records from polar ice, as well as with 14C measurements in planktonic foraminifera to assess air-sea exchanges of CO2. All these data will help to improve the calibration of the 14C radiochronometer, which is essential for tracing and quantifying processes in the carbon cycle.
The evolution of carbonate biogenic production has been shown to control the inorganic part of the oceanic carbon cycle over geological time, and its study is one of the strengths of the team. Recently, the ANR MioCarb project (2020-2024), led by Baptiste Suchéras-Marx, focuses on the study of this production during the late Miocene and early Pliocene. The study of the carbonate system in the carbon cycle has also recently been strengthened by the recruitment of Olivier Sulpis (CR CNRS; 2022).
Tom Chalk (CR CNRS; 2023), winner of an ERC-StG ForCry grant in 2022, will contribute to the analytical development of this theme with the analysis of stable boron isotopes. The application of this cutting-edge method will make it possible to reconstruct the pH and the evolution of atmospheric CO2 during the Neogene, with a view to reconstructing the evolution of the carbon cycle on a geological timescale.
Finally, the ANR-PRCI ORACLE project, funded in 2022 and led by Yannick Garcin, focuses on the study of soil carbon. ORACLE aims to reconstruct the Holocene history of peat in the Congo in order to gain a better understanding of the tropical carbon cycle and hydroclimatic dynamics in this region of the world.