Photosynthetic rates derived from satellite‐based chlorophyll concentration

Abstract

We assembled a dataset of 14 C‐based productivity measurements to understand the critical variables required for accurate assessment of daily depth‐integrated phytoplankton carbon fixation ( PP ( PP eu ) u ) from measurements of sea surface pigment concentrations ( C sat )( 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 ) z ) and those that control the optimal assimilation efficiency of the productivity profile ( P ( P B opt ). The VGPM accounted for 79% of the observed variability in P z and 86% of the variability in PP eu by using measured values of P B opt . Our results indicate that the accuracy of productivity algorithms in estimating PP eu 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.

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