Thanks Marcus Koehler, at this point I am collecting all available information. In the frame of EC-Earth4 (which uses oifsr43r3) I am interested in the global carbon cycle (land/ocean/atmosphere), while other EC-Earth colleagues (such as Philippe) are working on atmospheric chemistry.
For the atmosphere that would require a CO2 tracer (and other GHG eventually) and also a mass fixer (see Recommendations for mass fixers in OpenIFS?). Would having "new" passive tracers in oifs require something like OpenIFS/AC? I know in the ifs passive tracers are part of GEMS and I guess also in CAMS, but I am a bit in the dark on this wrt openifs.