Abstract
Accurate assessment of the various sources and sinks of carbon dioxide (CO2), especially terrestrial ecosystem and ocean fluxes with high uncertainties, is important for understanding of the global carbon cycle, supporting the formulation of climate policies, and projecting future climate change. Satellite retrievals of the column-averaged dry air mole fractions of CO2 (XCO2) are being widely used to improve carbon flux estimation due to their broad spatial coverage. However, there is no consensus on the robust estimates of regional fluxes. In this study, we present a global and regional resolved terrestrial ecosystem carbon flux (NEE) and ocean carbon flux dataset for 2015–2019. The dataset was generated using the Tan-Tracker inversion system by assimilating Observing Carbon Observatory 2 (OCO-2) column CO2 retrievals. The posterior NEE and ocean carbon fluxes were comprehensively validated by comparing posterior simulated CO2 concentrations with OCO-2 independent retrievals and Total Carbon Column Observing Network (TCCON) measurements. The validation showed that posterior carbon fluxes significantly improved the modelling of atmospheric CO2 concentrations, with global mean biases of 0.33 ppm against OCO-2 retrievals and 0.12 ppm against TCCON measurements. We described the characteristics of the dataset at global, regional, and Tibetan Plateau scales in terms of the carbon budget, annual and seasonal variations, and spatial distribution. The posterior 5-year annual mean global atmospheric CO2 growth rate was 5.35 PgC yr−1, which was within the uncertainty of the Global Carbon Budget 2020 estimate (5.49 PgC yr−1). The posterior annual mean NEE and ocean carbon fluxes were −4.07 and −3.33 PgC yr−1, respectively. Regional fluxes were analysed based on TransCom partitioning. All 11 land regions acted as carbon sinks, except for Tropical South America, which was almost neutral. The strongest carbon sinks were located in Boreal Asia, followed by Temperate Asia and North Africa. The entire Tibetan Plateau ecosystem was estimated as a carbon sink, taking up −49.52 TgC yr−1 on average, with the strongest sink occurring in eastern alpine meadows. These results indicate that our dataset captures surface carbon fluxes well and provides insight into the global carbon cycle. The dataset can be accessed at https://doi.org/10.11888/Meteoro.tpdc.271317 (Jin et al., 2021).
Highlights
Anthropogenic carbon dioxide (CO2) emissions are dominant sources for increasing atmospheric CO2 concentrations
We described the characteristics of the dataset at global, regional, and Tibetan Plateau scales in terms of the carbon budget, annual and seasonal variations, and spatial distribution
Inversions using gases Observing SATellite (GOSAT) 50 retrievals can significantly reduce the uncertainty of flux estimates in regions where surface CO2 observations are sparse; no agreement is achieved on the estimates of regional fluxes (Chevallier et al, 2014; Basu et al, 2013; Takagi et al, 2011)
Summary
Anthropogenic carbon dioxide (CO2) emissions are dominant sources for increasing atmospheric CO2 concentrations. Many inversion studies have utilized high-precision in situ and flask observations to infer surface CO2 fluxes (Peters et al, 2007; Chevallier et al, 2010; Lauvaux et al, 2016). Its higher measurement signal-to-noise ratio allows for higher-precision XCO2 retrievals, and its higher spatial sampling density facilitates validation using the ground-based Total Carbon Column Observing 55 Network (TCCON) (Liang et al, 2017; Wunch et al, 2017). Based on these characteristics, OCO-2 may provide better constraints on surface CO2 fluxes inversions (Basu et al, 2018). The effectiveness and potential of these constantly updated satellite retrievals for inferring surface CO2 fluxes requires further and persistent investigation
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