A novel data-driven global model of photosynthesis using solar-induced chlorophyll fluorescence

Abstract. Space-based vegetation indices have been used to model global photosynthesis for more than two decades. However, vegetation indices are linked to leaf optical properties rather than leaf physiology, which limits their utility in regions where changes in photosynthesis are driven by leaf development and demography. Conversely, solar-induced chlorophyll fluorescence contains information on leaf physiology and has been shown to be synchronous with photosynthetic activity. Here we present a novel model of global photosynthesis, ChloFluo, which uses spaceborne chlorophyll fluorescence to estimate the amount of photosynthetically active radiation (PAR) absorbed by chlorophyll (APAR_chl). ChloFluo is unique in that instead of estimating APAR_chl as a function of a vegetation index and an ancillary PAR product, we model APAR_chl using its empirical relationship with SIF and the proportion of APAR_chl that is reemitted as SIF, or ΦF. Potential uses of our model are to advance our understanding of the timing and magnitude of photosynthesis, its effect on atmospheric carbon dioxide fluxes, and vegetation response to climate events and change.