Estimating global gross primary productivity using chlorophyll fluorescence and a data assimilation system with the BETHY-SCOPE model

Abstract

Abstract. This paper presents the assimilation of solar-induced chlorophyll fluorescence (SIF) into a terrestrial biosphere model to estimate the gross uptake of carbon through photosynthesis (GPP). We use the BETHY-SCOPE model to simulate both GPP and SIF using a process-based formulation, going beyond a simple linear scaling between the two. We then use satellite SIF data from the Orbiting Carbon Observatory-2 (OCO-2) for 2015 in the data assimilation system to constrain model biophysical parameters and GPP. The assimilation results in considerable improvement in the fit between model and observed SIF, despite a limited capability to fit regions with large seasonal variability in SIF. The SIF assimilation increases global GPP by 31 % to 167±5 Pg C yr−1 and shows an improvement in the global distribution of productivity relative to independent estimates, but a large difference in magnitude. This change in global GPP is driven by an overall increase in photosynthetic light-use efficiency across almost all biomes and more minor, regionally distinct changes in APAR. This process-based data assimilation opens up new pathways to the effective utilization of satellite SIF data to improve our understanding of the global carbon cycle.

Effects of Anthropogenic Activity on Global Terrestrial Gross Primary Production

“…Similarly, Joiner et al () pointed out that better statistical correlation with eddy‐covariance data is achieved when satellite data are used at high spatial resolution, similar to the typical footprint of eddy covariance measurement sites of 1 km 2 . The annual GPP from BEAMS agrees well with a study that used chlorophyll fluorescence and estimated a GPP of 137 ± 6 Gt C/year in 2015 (Norton et al, ).…”

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

“…It has been shown that despite the local dominance, water-related NEE anomalies largely cancel spatially in RS+METEO and TRENDY, resulting in the dominance of temperature-related NEE anomalies in globally integrated land sink IAV , but see Humphrey et al, 2018, for a different perspective). Studies on effects of water availability on spatial GPP anomalies using the RS data yielded highly plausible patterns that were consistent with independent data (Flach et al, 2018;Orth et al, 2019;Walther Figure 7. Mean seasonal variations in net land carbon release for the period 2008-2010 over TRANSCOM regions.…”

“…Exploiting the massive space-based column CO 2 data in the future will hopefully facilitate improvements on this aspect. Despite large uncertainties and apparent knowledge gaps in NEE IAV from both an observational and modelling perspective, there are promising indications of improved capability to track IAV patterns with FLUXCOM such as the good correspondence of RS+METEO with inversions at the global scale and independent verifications of GPP IAV of RS at least outside the wet tropics (Flach et al, 2018;Joiner et al, 2018;Orth et al, 2019;Walther et al, 2019).…”

Terrestrial gross primary production: Using NIRV to scale from site to globe

“…One explanation for this pattern is that NIR V minimizes soil contamination that might cause alternative remote sensing approaches to systematically underestimate leaf area across the midlatitudes. Consistent with this view, a recent study that combined solar-induced chlorophyll fluorescence with a terrestrial ecosystem model reports similar relative increases in extratropical GPP (Norton et al, 2018).…”