Carbon storage estimates in vegetation and soil during the last 21 ka BP: a review of literature and new results based on data-model fusion

Guiot Joel

CNRS

The knowledge of carbon storage in vegetation and soil is crucial to close the carbon cycle. In particular, there is a strong interest to know carbon storage for two extreme periods of the past: the Last Glacial Maximum (LGM, ~21 ka BP) and mid-Holocene (MH, ~6 ka BP). We will review the various estimates done for the last two decades by different methods, pollen, carbon isotopes, general circulation model (GCM) analysis and vegetation models. The discrepancies are significant. This may be due to the fact that these methods do not synthetically take into account significant differences in climate distribution between modern and past conditions, as well as the effects of atmospheric CO2 concentrations on vegetation. Finally, we propose a new method to estimate past biospheric carbon stocks, based on a new integrated ecosystem model (PCM) built on a physiological process vegetation model (BIOME4) coupled with a process-based biospheric carbon model (DEMETER). To improve the fit between the data and the model, we use a data-model fusion technique, where the PCM is constrained to fit pollen data. The carbon model is validated with present-day observations of vegetation biomes and soil carbon, and the data-model scheme is tested against surface pollen spectra sample sites from most of the continents. Results for LGM and MH are presented and discussed according to previous estimates.