Terrestrial Carbon Flux Dynamics in the Southern American Temperate Region: Insights from Dynamic Global Vegetation Models and GOSAT XCO2 Measurements

Understanding terrestrial carbon fluxes is a prerequisite for accurately predicting the global biospheric uptake and release of CO₂ under climate change and other environmental stressors. Terrestrial carbon fluxes in the southern hemisphere still exhibit quite large uncertainties due to limited measurements and a lack of comprehensive process understanding. This study focuses on the South American Temperate (SAT) region, employing various Dynamic Global Vegetation Model (DGVM) models (TRENDY v9) to investigate carbon flux dynamics. We find significant discrepancies between these DGVM models in terms of both phasing and magnitude. To address this, atmospheric XCO₂ measurements from the Greenhouse Gases Observing Satellite (GOSAT) during the period 2009-2018 are incorporated into an atmospheric inversion using the model TM5-4DVar to obtain net CO₂ fluxes. We identify DGVM models that match the inversion results, particularly showing the same phasing and similar magnitude of net ecosystem exchange (NEE) as the inversion results. The matching DGVMs show that the increase in NEE during the mid of the year is driven by an early increase in heterotrophic respiration whereas the autotrophic respiration remains in phase with the gross primary production (GPP) and is delayed with respect to heterotrophic respiration. The observed flux behavior is linked to the onset of rainfall in the semi-arid regions of SAT, resembling findings in Australia by Metz et al. (2023). We hypothesize that soil rewetting processes in semi-arid areas play an important role in constraining the global carbon budget and should be represented more accurately in global carbon cycle models to improve the estimation of the global carbon budget.  

 

Metz, E.-M., Vardag, S.N., Basu, S., Jung, M., Ahrens, B., El-Madany, T., Sitch, S., Arora, V.  K., Briggs, P. R., Friedlingstein, P., Goll, D.S., Jain, A.K.,  Kato, E., Lombardozzi, D., Nabel,J .E. M. S., Poulter, B., Séférian, R., Tian, H., Wiltshire, A., Yuan, W., Yue, X., Zaehle, S.,  Deutscher, N.M.,  Griffith, D.W.T., Butz, A. Soil respiration–driven CO2 pulses dominate Australia’s flux variability. Science, 379, 1332-1335, https://doi.org/10.1126/science.add7833, 2023.