A 10-year global monthly averaged terrestrial net ecosystem exchange dataset inferred from the ACOS GOSAT v9 XCO2 retrievals (GCAS2021)
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abstract
Abstract. A global gridded net ecosystem exchange (NEE) of CO2
dataset is vital in global and regional carbon cycle studies. Top-down
atmospheric inversion is one of the major methods to estimate the global
NEE; however, the existing global NEE datasets generated through inversion
from conventional CO2 observations have large uncertainties in places
where observational data are sparse. Here, by assimilating the GOSAT ACOS v9
XCO2 product, we generate a 10-year (2010–2019) global monthly
terrestrial NEE dataset using the Global Carbon Assimilation System, version
2 (GCASv2), which is named GCAS2021. It includes gridded (1∘×1∘), globally, latitudinally, and regionally
aggregated prior and posterior NEE and ocean (OCN) fluxes and prescribed
wildfire (FIRE) and fossil fuel and cement (FFC) carbon emissions. Globally,
the decadal mean NEE is -3.73±0.52 PgC yr−1, with an interannual
amplitude of 2.73 PgC yr−1. Combining the OCN flux and FIRE and FFC
emissions, the net biosphere flux (NBE) and atmospheric growth rate (AGR) as
well as their inter-annual variabilities (IAVs) agree well with the
estimates of the Global Carbon Budget 2020. Regionally, our dataset shows that
eastern North America, the Amazon, the Congo Basin, Europe, boreal forests, southern
China, and Southeast Asia are carbon sinks, while the western United States, African
grasslands, Brazilian plateaus, and parts of South Asia are carbon sources.
In the TRANSCOM land regions, the NBEs of temperate N. America, northern
Africa, and boreal Asia are between the estimates of CMS-Flux NBE 2020 and
CT2019B, and those in temperate Asia, Europe, and Southeast Asia are
consistent with CMS-Flux NBE 2020 but significantly different from CT2019B.
In the RECCAP2 regions, except for Africa and South Asia, the NBEs are
comparable with the latest bottom-up estimate of Ciais et al. (2021).
Compared with previous studies, the IAVs and seasonal cycles of NEE of this
dataset could clearly reflect the impacts of extreme climates and
large-scale climate anomalies on the carbon flux. The evaluations also show
that the posterior CO2 concentrations at remote sites and on a regional
scale, as well as on vertical CO2 profiles in the Asia-Pacific region,
are all consistent with independent CO2 measurements from surface flask
and aircraft CO2 observations, indicating that this dataset captures
surface carbon fluxes well. We believe that this dataset can contribute to
regional- or national-scale carbon cycle and carbon neutrality assessment
and carbon dynamics research. The dataset can be accessed at
https://doi.org/10.5281/zenodo.5829774 (Jiang, 2022).
