Photosynthetic rates derived from satellite-based chlorophyll concentration

We assembled a dataset of C-14-based productivity measurements to understand the critical variables required for accurate assessment of daily depth-integrated phytoplankton carbon fixation (PPeu) from measurements of sea surface pigment concentrations (C-sat). From this dataset, we developed a light-dependent, depth-resolved model for carbon fixation (VGPM) that partitions environmental factors affecting primary production into those that influence the relative vertical distribution of primary production (P-z) and those that control the optimal assimilation efficiency of the productivity profile (P-opt(B)). The VGPM accounted for 79% of the observed variability in P-z and 86% of the variability in PPeu by using measured values of P-opt(B). Our results indicate that the accuracy of productivity algorithms in estimating PPeu is dependent primarily upon the ability to accurately represent variability in P-opt(B). We developed a temperature-dependent P-opt(B), model that was used in conjunction with monthly climatological images of C-sat, sea surface temperature, and cloud-corrected estimates of surface irradiance to calculate a global annual phytoplankton carbon fixation (PPannu) rate of 43.5 Pg C yr(-1). The geographical distribution of PPannu was distinctly different than results from previous models. Our results illustrate the importance of focusing P-opt(B) model development on temporal and spatial, rather than the vertical, variability.