Soil CO2 efflux simulations using Monte Carlo method and implications for recording paleo-atmospheric PCO2 in pedogenic gibbsite
Abstract Monte Carlo simulation testing of the sensitivity of the Fickian diffusion model used for paleo-PCO 2 proxies indicates that assuming annual average soil respiration rate results in over-estimation of PCO 2 . In all cases, the natural variability of the factors of the model, including soil porosity and inverse tortuosity and the δ 13 C value of the soil produced CO 2 were not able to account for discrepancies between measured δ 13 C values from a modern soil and modeled results using established assumptions. Assuming that there is negligible carbon isotope fractionation during the occlusion of CO 2 in pedogenic gibbsite, the flaw in the model appears to be the assumed value of soil respiration rate. If correct, the implication is that previous paleo-PCO 2 estimates from soil hydroxides may be too high by as much as a factor of ten.