This work area focuses on the past and future evolution of climate forcings and the links with the different compartments of the carbon cycle.
The main external climate forcings are reconstructed at very high resolution for the late Pleistocene from continental archives: variations of solar forcings derived from cosmogenic isotopes in ice (10Be, 36Cl) and trees (14C); variations of volcanic forcings derived from continental and glacial archives (detection of stratospheric volcanic eruptions with 10Be and ice chemistry). The reconstructions of these solar and volcanic forcings are part of the forcings used for the climate models whose simulations are synthesized by the IPCC.
The carbon cycle is approached under different aspects. The 14C analysis of micro-samples allows the separation of natural and anthropogenic sources of carbonaceous aerosols which have an influence on the local and global climate, as well as on the health of populations (EQUIPEX ASTER-CEREGE project). On the other hand, the measurement of 14C of carbonates and organic compounds varied in oceanic sediments or corals, allows us to evaluate the residence time of the different reservoirs of the carbon cycle over the last 50,000 years (EQUIPEX ASTER-CEREGE project). The variations of the carbon cycle are also studied from the high resolution measurement of the 14C content of subfossil woods during the last deglaciation and the Holocene (ANR CARBOTRYDH project). The carbon cycle in soils is also studied by improving the global modeling of carbon exchanges between the atmosphere and soils by taking into account the impact of climate change (precipitation) and land use changes, as well as feedbacks for climate change mitigation. This approach involves the quantification of soil organic carbon turnover, using 13C and 14C natural isotope tracings (total or molecular C). The spatial scale of these studies is global, with specific expertise for the intertropical zone and temperate agrosystems. All these advances are made possible by technical developments made with the AixMICADAS gas pedal for the analysis of micro-samples (carbonates and organic matter).
This axis also focuses on the study of the carbon cycle during the major climatic transitions of the Cenozoic (65-0 Ma): Eocene-Oligocene transition (34 Ma) and Middle Miocene-Terminal Miocene transition (15-5 Ma). The interactions between the establishment of the Antarctic ice sheet, the intensification of the Asian monsoons and the marine carbon cycle are studied through the joint use of the Earth System model developed by IPSL, adapted for "paleo" and proxies applications (ANR AMOR, 2016-2021, PI Y. Donnadieu; ERC MAGIC). In this framework, in the Miocene, paleo-pCO2 is reconstructed thanks to stable isotopes in coccoliths, and its variation integrated for process understanding (ANR iMonsoon). Finally, the study of the production and accumulation of pelagic biogenic carbonates during the Meso-Cenozoic will allow us to determine the forcing and interactions between climate, biological evolution and carbon cycle.
All of these activities are carried out in collaboration with the other thematic teams: Earth & Planets (for solar and volcanic forcing), Sustainable Environment (for the carbon cycle in soils) and Resources, Reservoirs, Hydrosystems (for the carbon cycle in the long term).