## 5 Conclusions  
The OCO-2 provides SIF soundings with a small footprint (1.3 km \(\times\) 2.25 km), offering a valuable opportunity to establish a more robust relationship between SIF measured from space and GPP data from flux towers. However, generating finer-resolution global GPP estimates from OCO-2 SIF was hindered by OCO-2's sparse coverage and reliable SIF-GPP relationship. In this study, we developed a continuous gridded global GPP data product (GOSIF GPP) for the period 2000-2017 from the recently-generated global, OCO-2 based SIF product (GOSIF) with fine-resolution (i.e., 0.05\({}^{\circ}\), 8-day) using a set of SIF-GPP relationships. Our results showed that all of the eight SIF-GPP relationships could estimate GPP fairly well, and the ensemble mean 8-day GPP based on the eight SIF-GPP relationships was generally highly correlated with flux tower GPP for 91 FLUXNET sites across the globe (R\({}^{2}\)=0.74, RMSE = 1.92 g C m\({}^{-2}\) d\({}^{-1}\)). The ensemble mean GPP showed reasonable spatial and seasonal variations across the globe, and fully captured both spatial and seasonal patterns present in the coarse-resolution (1\({}^{\circ}\)) GPP estimates based on coarse-resolution SIF data directly aggregated from discrete OCO-2 soundings. Our results showed that the difference in annual GPP based on a universal versus biome-specific relationship was generally small across the globe, while the magnitude of the annual GPP could be significantly influenced by whether the intercept was forced to be zero. Our global GPP estimate (135.5 \(\pm\) 8.8 Pg C yr\({}^{-1}\)) is between the median estimate of non-process based methods and the median estimate of process-based models. Significant interannual variability in GPP was observed in many parts of the globe. Annual GPP also exhibited increasing trends in many areas, particularly in the Northern Hemisphere. The different SIF-GPP relationships could lead to significant differences in annual GPP, particularly in the tropics. The further elucidation of the SIF-GPP relationship is expected to reduce the uncertainty of the resulting GPP estimates. Our SIF-based method is a new and independent approach for estimating terrestrial photosynthesis regionally and globally. With the availability of high-quality, gridded SIF observations from space (e.g., TROPOMI, FLEX), this novel approach can lead to gridded GPP estimates solely based on SIF observations and does not rely on any input data (e.g., climate data, soil properties). The use of a universal SIF-GPP relationship can also avoid the uncertainty associated with land cover maps. Our approach can potentially lead to more accurate, near real-time GPP estimates regionally and globally. Our novel, fine-resolution GPP product (GOSIF GPP), freely available at our data repository ([[http://globalecology.unh.edu](http://globalecology.unh.edu)]([http://globalecology.unh.edu](http://globalecology.unh.edu))), will be valuable for studying ecosystem functioning and carbon cycling, monitoring agricultural production, informing ecosystem management, and benchmarking state-of-the-art terrestrial biosphere/Earth system models (ESMs). The following are available online at [[http://www.mdpi.com/2072-4292/11/21/2563/s1](http://www.mdpi.com/2072-4292/11/21/2563/s1)]([http://www.mdpi.com/2072-4292/11/21/2563/s1](http://www.mdpi.com/2072-4292/11/21/2563/s1)), Figure S1: Spatial patterns of R\({}_{2}\) and RMSE between our ensemble mean 8-day GPP and flux tower GPP for each site, Figure S2: Validation of ensemble mean annual GPP against EC-MOD GPP in 2010, Figure S3. Validation of the interannual variability of GOSIF GPP for each site, Figure S4: Spatial patterns of our global ensemble mean GPP from January through December in 2016, Figure S5: Spatial patterns and magnitude of global maximum GPP, Table S1: FLUXNET Tier-1 sites used for validating the gridded GPP estimates in this study, Table S2: Estimates of annual global GPP based on both non-process methods and process-based models.