Photosynthetic rates derived from satellite-based chlorophyll concentration

Abstract

We assembled a dataset of 14C-based productivity measurements to understand the critical variables required for accurate assessment of daily depth-integrated phytoplankton carbon fixation (PP(cu)) 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(B)(opt)). The VGPM accounted for 79% of the observed variability in P(z) and 86% of the variability in PP(cu) by using measured values of P(B)(opt). Our results indicate that the accuracy of productivity algorithms in estimating PP(cu) is dependent primarily upon the ability to accurately represent variability in P(B)(opt). We developed a temperature-dependent P(B)(opt) 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 (PP(annu)) rate of 43.5 Pg C yr-1. The geographical distribution of PP(annu) was distinctly different than results from previous models. Our results illustrate the importance of focusing P(B)(opt), model development on temporal and spatial, rather than the vertical, variability.