PHOTOSYNTHETIC RATES DERIVED FROM SATELLITE-BASED CHLOROPHYLL CONCENTRATION

We assembled a dataset of C-14-based productivity measurements to unde rstand the critical variables required for accurate assessment of dail y depth-integrated phytoplankton carbon fixation (PPeu) from measureme nts of sea surface pigment concentrations (C-sat). From this dataset, we developed a light-dependent, depth-resolved model for carbon fixati on (VGPM) that partitions environmental factors affecting primary prod uction into those that influence the relative vertical distribution of primary production (P-z) and those that control the optimal assimilat ion efficiency of the productivity profile (P-opt(B)). The VGPM accoun ted for 79% of the observed variability in P-z and 86% of the variabil ity in PPeu by using measured values of P-opt(B). Our results indicate that the accuracy of productivity algorithms in estimating PPeu is de pendent primarily upon the ability to accurately represent variability in P-opt(B). We developed a temperature-dependent P-opt(B), model tha t was used in conjunction with monthly climatological images of C-sat, sea surface temperature, and cloud-corrected estimates of surface irr adiance to calculate a global annual phytoplankton carbon fixation (PP annu) rate of 43.5 Pg C yr(-1). The geographical distribution of PPann u was distinctly different than results from previous models. Our resu lts illustrate the importance of focusing P-opt(B) model development o n temporal and spatial, rather than the vertical, variability.