Disequilibrium of terrestrial ecosystem CO<sub>2</sub> budget caused by disturbance-induced emissions and non-CO<sub>2</sub> carbon export flows: a global model assessment

Abstract

Abstract. The global carbon budget of terrestrial ecosystems is chiefly determined by major flows of carbon dioxide (CO2) such as photosynthesis and respiration, but various minor flows exert considerable influence in determining carbon stocks and their turnover. This study assessed the effects of eight minor carbon flows on the terrestrial carbon budget using a process-based model, the Vegetation Integrative SImulator for Trace gases (VISIT), which included non-CO2 carbon flows, such as methane and biogenic volatile organic compound (BVOC) emissions and subsurface carbon exports and disturbances such as biomass burning, land-use changes, and harvest activities. The range of model-associated uncertainty was evaluated through parameter-ensemble simulations and the results were compared with corresponding observational and modeling studies. In the historical period of 1901–2016, the VISIT simulation indicated that the minor flows substantially influenced terrestrial carbon stocks, flows, and budgets. The simulations estimated mean net ecosystem production in 2000–2009 as 3.21±1.1 Pg C yr−1 without minor flows and 6.85±0.9 Pg C yr−1 with minor flows. Including minor carbon flows yielded an estimated net biome production of 1.62±1.0 Pg C yr−1 in the same period. Biomass burning, wood harvest, export of organic carbon by water erosion, and BVOC emissions had impacts on the global terrestrial carbon budget amounting to around 1 Pg C yr−1 with specific interannual variabilities. After including the minor flows, ecosystem carbon storage was suppressed by about 440 Pg C, and its mean residence time was shortened by about 2.4 years. The minor flows occur heterogeneously over the land, such that BVOC emission, subsurface export, and wood harvest occur mainly in the tropics, and biomass burning occurs extensively in boreal forests. They also differ in their decadal trends, due to differences in their driving factors. Aggregating the simulation results by land-cover type, cropland fraction, and annual precipitation yielded more insight into the contributions of these minor flows to the terrestrial carbon budget. Considering their substantial and unique roles, these minor flows should be taken into account in the global carbon budget in an integrated manner.

Miroc4を基にした化学輸送モデルと逆解法とを用いた大気中一酸化二窒素の動態解析

“…They estimated emissions of 5.1 (range: 3.1-7.2) TgN yr -1 from global oceans and 10.8 (range: 9.3-12.5) TgN yr -1 from global land for 2000-2009 by inverse (top-down) modelling, and bottom-up global total emission of 16.4 (range:12.3-22.4) TgN yr -1 . Bottom-up emission estimations are based on inventory emissions for various activity sectors and process modelling of terrestrial and ocean biogeochemical cycles (Bouwman et al 2013;Buitenhuis et al 2018;Butterbach-Bahl et al 2013;Ito, 2019;Winiwarter et al 2018). Over the past few decades, large and systematic efforts have resulted in an evolution of sea-air N2O emission distribution based on oceanic pN2O upscaling and empirical modelling (Manizza et al 2012;Nevison at al.…”

Estimation of fire-induced carbon emissions from Equatorial Asia in 2015 using in situ aircraft and ship observations

“…Note that both the datasets use similar emission factors of CO 2 and CO based on Akagi et al (2011); in particular, the same emission factor from Christian et al ( 2003) was applied to peatland, from which a large part of the fires arise in Equatorial Asia (van der . The rest of the CO fluxes from fossil fuel use and vegetation were derived from the Emission Database for Global Atmospheric Research (EDGAR) version 4.3.2 (Janssens-Maenhout et al, 2019) and the process-based model of terrestrial ecosystems, the Vegetation Integrative SImulator for Trace gases (VISIT; Ito and Inatomi, 2012;Ito, 2019), respectively. In the VISIT simulation, CO emissions are estimated with the scheme of Guenther (1997) but using an emission factor by Tao and Jain ( 2005).…”

Estimated regional CO<sub>2</sub> flux and uncertainty based on an ensemble of atmospheric CO<sub>2</sub> inversions

“…CO2 ff is simulated using the gridded fossil fuel emission dataset (GridFED; Jones et al, 2021). CO2 lnd tracers are simulated using two sets of terrestrial biosphere fluxes from the Carnegie-Ames-Stanford Approach (CASA) biogeochemical model (Randerson et al, 1997)), and Vegetation Integrative Simulator for Trace Gases (VISIT) (Ito, 2019). The CASA fluxes are annually balanced, seasonally varying flux due to terrestrial photosynthesis and respiration, while the VISIT simulation accounts for CO2 fertilisation (increasing photosynthesis due to rising atmospheric CO2), LUC (perturbation on terrestrial carbon budget via land-use change), and climate variability (on the net a large land sink; Table 1).…”