On what scales can GOSAT flux inversions constrain anomalies in terrestrial ecosystems?

Abstract

Abstract. Interannual variations in temperature and precipitation impact the carbon balance of terrestrial ecosystems, leaving an imprint in atmospheric CO2. Quantifying the impact of climate anomalies on the net ecosystem exchange (NEE) of terrestrial ecosystems can provide a constraint to evaluate terrestrial biosphere models against and may provide an emergent constraint on the response of terrestrial ecosystems to climate change. We investigate the spatial scales over which interannual variability in NEE can be constrained using atmospheric CO2 observations from the Greenhouse Gases Observing Satellite (GOSAT). NEE anomalies are calculated by performing a series of inversion analyses using the GEOS-Chem adjoint model to assimilate GOSAT observations. Monthly NEE anomalies are compared to “proxies”, variables that are associated with anomalies in the terrestrial carbon cycle, and to upscaled NEE estimates from FLUXCOM. Statistically significant correlations (P<0.05) are obtained between posterior NEE anomalies and anomalies in soil temperature and FLUXCOM NEE on continental and larger scales in the tropics, as well as in the northern extratropics on subcontinental scales during the summer (R2≥0.49), suggesting that GOSAT measurements provide a constraint on NEE interannual variability (IAV) on these spatial scales. Furthermore, we show that GOSAT flux inversions are generally better correlated with the environmental proxies and FLUXCOM NEE than NEE anomalies produced by a set of terrestrial biosphere models (TBMs), suggesting that GOSAT flux inversions could be used to evaluate TBM NEE fluxes.

Contrasting Regional Carbon Cycle Responses to Seasonal Climate Anomalies Across the East‐West Divide of Temperate North America

“…To a large extent, IAV in the carbon balance of ecosystems is expected to be driven by IAV in temperature and moisture (Berry & Bjorkman, 1980; Byrne et al, 2019; Smith et al, 2011); thus, we examine the relationship between CO 2 flux anomalies and anomalies in soil temperature (ΔT) and soil moisture (ΔM). Figure 4 shows the correlation between ΔGPP and anomalies in climate variables over 2001–2017.…”

“…Recently, space‐based measurements of column‐averaged dry‐air mole fractions of CO 2 ( ) have allowed for much expanded observational of coverage, leading to top‐down NEE constraints on smaller spatial scales (Bowman et al, 2017; Byrne et al, 2017, 2019, 2020; Guerlet et al, 2013; Ishizawa et al, 2016; Liu et al, 2017; Liu, Bowman, Parazoo, et al, 2018). Furthermore, advances in remote sensing techniques have allowed for more reliable GPP estimates from space from solar‐induced fluorescence (SIF) measurements (Byrne et al, 2018; Frankenberg et al, 2011; Joiner et al, 2011; Parazoo et al, 2014; Sun et al, 2017; Yang et al, 2015) and up‐scaled flux tower GPP estimates using MODIS observations (Joiner et al, 2018; Jung et al, 2020).…”

Scaling carbon fluxes from eddy covariance sites to globe: synthesis and evaluation of the FLUXCOM approach

“…This suggests that neither CO 2 advection nor the light inhibition of leaf respiration appears to generate sizable biases of global GPP in FLUXCOM -a tendency likely encouraged by the relatively strict quality control on the EC flux data (Tramontana et al, 2016). Furthermore, a comparison of EC-based GPP with biometric GPP estimates across 18 globally distributed sites showed good agreement and no significant bias (Campioli et al, 2016). A recent study using partitioning based on carbonyl sulfide (COS) for four contrasting European sites also showed good agreement with standard EC-based GPP where systematic differences for mean GPP were < 5 % (Spielmann et al, 2019).…”

“…This is likely due to (1) a combination of sparse satellite data availability, cloud contamination and geometrical illumination effects in the tropics or (2) that the processes governing NEE IAV in the tropics cannot be captured by satellitebased predictors alone in RS (even under ideal observational conditions) but require additional meteorological variables such as temperature that are included in the RS+METEO setup. Some support for the latter point comes from Byrne et al (2019), who found strong correlations of anomalies from GOSAT inversions with NEE from RS+METEO and soil temperatures in the tropics but not with SIF and a drought indicator, suggesting that temperature impacts respiration more than photosynthesis in the tropics.…”

Cropland Carbon Uptake Delayed and Reduced by 2019 Midwest Floods

“…From the top‐down, measurements of the atmospheric CO 2 can provide constraints on net ecosystem exchange (NEE)—the net exchange of CO 2 between an ecosystem and the atmosphere, determined as autotrophic and heterotrophic respiration minus GPP (Bolin & Keeling, ; Gurney et al, ; Yin et al, ). Space‐based measurements of column‐averaged dry‐air mole fractions of CO 2 (X CO2 ) have been shown to provide information on NEE anomalies at large subcontinental scales (Byrne et al, ; Byrne et al, ; Guerlet et al, ; Ishizawa et al, ; Liu, Bowman, et al, ; Liu et al, ; Yin et al, ) and for point sources (Nassar et al, ; Schwandner et al, ) but are untested on smaller regional scales, such as the Midwest croplands. The Orbiting Carbon Observatory 2 (OCO‐2), launched in 2014, provides X CO2 to monitor the atmospheric signal of the event.…”