Titre du projet en anglais New constraints on climate changes inferred from past variability of the CO budget – COCLICO

Many reactive species characterized by relatively short lifetimes (in the range of few weeks to few months) indirectly influence the climate system by affecting the cleansing power of the atmosphere and cycles of major atmospheric greenhouse gases. Notably, carbon monoxide (CO) plays a central role within the climate-chemistry interactions. CO directly affects atmospheric levels of OH radicals. Furthermore, carbon monoxide has a significant indirect warming potential due to its impact on the budgets of methane and ozone. In the framework of the project COCLICO, characterizations of polar archives and modeling of the biogeochemical cycle of CO (0D and 2D) will be associated to constrain the budget of this species and its evolutions related to past climate variability and modern anthropogenic influences. Groundbreaking laser-based sensors will be implemented to infer past evolutions of both mixing and isotopic ratios of CO over specific time periods from polar archives (firn air and ice cores). A laser spectrometer (Optical-Feedback Cavity-Enhanced Absorption Spectrometer, OF-CEAS) operating at 2.33 um will be designed and associated with a CFA (Continuous Flow Analysis) melting system for continuous analysis of CO mixing ratio in air extracted from ice cores. Measurements of organic tracers will be performed along with CO analysis in Greenlandic ice to evaluate possible perturbations of the CO signal due to in situ production. OF-CEAS will be implemented at 4.33 um. CO isotopic analysis will be performed with a new cryogenic vacuum extraction system specifically designed for small gaseous samples (e.g. ~100 cm3) which will be linked to an OF-CEAS spectrometer operating at 4.33 um (implementation of a quantum cascade laser). A 2D chemistry model will be constrained by these new descriptions of CO mixing and isotopic ratio evolutions for simulations at middle and high southern latitudes. Although this model is already available, particular developments dedicated to CO will be implemented. Specifically, the impact of anthropogenic CO emissions will be investigated during the industrial period (1850-present) to reduce current uncertainties in radiative forcing due to tropospheric ozone, a major greenhouse gas. The impact of large climate changes on the CO and methane budgets as well as the oxidizing capacity of the atmosphere will be addressed by investigating the last glacial maximum (21 000 BP) and its climatic transition (21 000 - 10 000 BP). Relevant questions include why methane concentrations varied by up to 40 % during the last glacial-interglacial transition, and to what extend changes in fire regimes could have influenced the climate-chemistry interactions. More widely, the CO data collected in the framework of the project COCLICO will provide important constraints for global 3D coupled chemistry-climate models run under past climatic conditions.