DOC-PAST · Deciphering the Oxidizing Capacity of the PAST atmosphere

Atmospheric chemistry is an essential component of the functioning of the Earth's climate. It determines the atmospheric lifetime of most climatic agents, impacting the nature and concentrations of aerosols, greenhouse gases, cloud formations. Determining how this chemical reactivity has evolved in the past is essential, both for evaluating chemistry-climate models (CCM) and for establishing future climate trajectories. The chemical activity of the atmosphere is driven by highly reactive atmospheric compounds that have a very short lifetime in the atmosphere. Because of this ephemeral nature, they are not archived in the paleoclimate record. Reconstructing this chemical activity over time remains a difficult exercise that has not been successful to date. Using ice cores, the multidisciplinary DOC-PAST project proposes to develop new tracers of this chemical activity by taking advantage of the revolution introduced by clumps and isotopic anomalies. The aim is to use a variety of ice cores covering all latitudes to highlight key elements of the chemical reactivity of the atmosphere. This will be done by 1-determining in the laboratory the isotopic characteristics of key oxidation reactions of atmospheric of compounds preserved in the ice, 2-documenting in the ice archives these isotopic compositions and deducing the associated chemical reactivity of the atmosphere 3-incorporating in the CCM LMDz-INCA these changes and measuring their impacts on climate. These new isotopic proxies will require the development of new analytical approaches based on the retargeting of an orbitrap towards isotopic measurements and the construction of a very high sensitivity infrared spectrometer, paving the way for the use of clumped isotope in broad disciplinary fields using stable isotopes. DOC-PAST will provide for the first time in situ “chirurgical-level” of how atmospheric species are made with unparalleled mechanistic details and set new standards in geochemistry and spectroscopy.