The ICORDA project aimed to develop new and more accurate dating tools for deep ice cores, with the goal of improving the temporal reconstruction of climatic events during the last 800,000 years. By combining these tools with high- and low-latitude climate proxies, the project sought to establish clearer sequences of environmental change during past climate transitions.
A major focus was the development and calibration of the δ¹⁸O of O2 and δO2/N2 orbital dating proxies, measured in air bubbles trapped in ice. This involved designing a new optical spectrometry instrument capable of continuously measuring elemental and isotopic O2 composition with high precision (Piel et al., 2024). To study biological fractionation of atmospheric O2, new chambers quantified O2 fractionation during photosynthesis and respiration in various plant species (Paul et al., 2023). Continuous measurements enabled updated fractionation coefficients (Paul et al., 2025), incorporated into a box model to better interpret δ¹⁸O of O2 variations as dating tools and tracers of low-latitude hydrology. Additional modelling included incorporation of O2 isotopes into the ocean component of the iLOVECLIM model (PhD of E. Clermont), and new firn and snow models linking air transport, densification, and physical properties, guided by Antarctic firn-air pumping campaigns (PhD of R. Harris-Stuart; Harris-Stuart et al., 2024).
Parallel work focused on robust noble-gas dating, targeting argon and krypton isotopes. New extraction and purification lines accommodated various ice sample sizes for ⁴⁰Ar and ⁸¹Kr analysis. Krypton measurements were carried out at Hefei University, argon at LSCE, and both evaluated during I. Crotti’s PhD using TALDICE samples. The project also addressed limitations of the ⁴⁰Ar method by analysing deep ice from Antarctic and Greenland sites, with key results published for TALDICE and EPICA Dome C (Crotti et al., 2021; Bouchet et al., 2023).
Multi-proxy analyses of glacial terminations, based on EPICA Dome C records and Beyond EPICA material, formed the third major component. Despite COVID-19 delays, initial results on the penultimate deglaciation were delivered in early 2025. ICORDA researchers reconstructed temporal sequences linking source-region evaporation, Antarctic temperature, atmospheric CO2, and global photosynthesis over the last nine terminations (Landais et al., 2021; Grisart et al., 2022; Yang et al., 2022). A key output was the AICC2023 chronology (Bouchet et al., 2023), synthesising δO2/N2, Total Air Content, δ¹⁸O of O2, and δ¹⁵N of N2. Additional work refined the CO2–temperature timing and constrained sea-level and CO2 phasing uncertainties over the past 640,000 years (Auriol et al., in press).
To support Beyond EPICA analyses, the project developed a low-pressure optical spectrometry prototype for continuous δ¹⁸O of O2 measurements on small air volumes, building on the 2024 instrument. Full campaigns for Beyond EPICA are planned for February 2026.
