The Carbon, Absorption, and Fluorescence Euphotic‐resolving (CAFE) net primary production model is an adaptable framework for advancing global ocean productivity assessments by exploiting state‐of‐the‐art satellite ocean color analyses and addressing key physiological and ecological attributes of phytoplankton. Here we present the first implementation of the CAFE model that incorporates inherent optical properties derived from ocean color measurements into a mechanistic and accurate model of phytoplankton growth rates (μ) and net phytoplankton production (NPP). The CAFE model calculates NPP as the product of energy absorption (Q_PAR), and the efficiency (ϕ_μ) by which absorbed energy is converted into carbon biomass (C_Phyto), while μ is calculated as NPP normalized to C_Phyto. The CAFE model performance is evaluated alongside 21 other NPP models against a spatially robust and globally representative set of direct NPP measurements. This analysis demonstrates that the CAFE model explains the greatest amount of variance and has the lowest model bias relative to other NPP models analyzed with this data set. Global oceanic NPP from the CAFE model (52 Pg C m⁻² yr⁻¹) and mean division rates (0.34 day⁻¹) are derived from climatological satellite data (2002–2014). This manuscript discusses and validates individual CAFE model parameters (e.g., Q_PAR and ϕ_μ), provides detailed sensitivity analyses, and compares the CAFE model results and parameterization to other widely cited models.

Phytoplankton physiology is dynamic and highly responsive to the environment. Phytoplankton acclimate to changing environmental conditions by a complex reallocation of carbon and energy through metabolic pathways to optimize growth. Considering the tremendous diversity of phytoplankton, it is not surprising that different phytoplankton taxa use different strategies to partition carbon and energy resources. It has therefore been satisfying to discover that general principles of energetic stoichiometry appear to govern these complex processes and can be broadly applied to interpret phytoplankton distributions, productivity, and food web dynamics. The expectation of future changes in aquatic environments brought on by climate change warrants gathering knowledge about underlying patterns of photosynthetic energy allocation and their impacts on community structure and ecosystem productivity.

Phytoplankton growth and productivity relies on light, multiple nutrients and temperature. These combined factors constitute the ‘integrated growth environment’. Since their emergence in the Archaean ocean, phytoplankton have experienced dramatic shifts in their integrated growth environment and, in response, evolved diverse mechanisms to maximize growth by optimizing the allocation of photosynthetic resources (ATP and NADPH) among all cellular processes. Consequently, co-limitation has become an omnipresent condition in the global ocean. Here we focus on evolved phytoplankton populations of the contemporary ocean and the varied energetic pathways they employ to solve the optimization problem of resource supply and demand. Central to this discussion is the allocation of reductant formed through photosynthesis, which we propose has the following three primary fates: carbon fixation, direct use and ATP generation. Investment of reductant among these three sinks is tied to cell cycle events, differentially influenced by specific forms of nutrient stress, and a strong determinant of relationships between light-harvesting (pigment), photosynthetic electron transport and carbon fixation. Global implications of optimization are illustrated by deconvolving trends in the 10-year global satellite chlorophyll record into contributions from biomass and physiology, thereby providing a unique perspective on the dynamic nature of surface phytoplankton populations and their link to climate.

The SAR11 Alphaproteobacteria are the most abundant heterotrophs in the oceans and are believed to play a major role in mineralizing marine dissolved organic carbon. Their genomes are among the smallest known for free-living heterotrophic cells, raising questions about how they successfully utilize complex organic matter with a limited metabolic repertoire. Here we show that conserved genes in SAR11 subgroup Ia (Candidatus Pelagibacter ubique) genomes encode pathways for the oxidation of a variety of one-carbon compounds and methyl functional groups from methylated compounds. These pathways were predicted to produce energy by tetrahydrofolate (THF)-mediated oxidation, but not to support the net assimilation of biomass from C1 compounds. Measurements of cellular ATP content and the oxidation of ¹⁴C-labeled compounds to ¹⁴CO₂ indicated that methanol, formaldehyde, methylamine, and methyl groups from glycine betaine (GBT), trimethylamine (TMA), trimethylamine N-oxide (TMAO), and dimethylsulfoniopropionate (DMSP) were oxidized by axenic cultures of the SAR11 strain Ca. P. ubique HTCC1062. Analyses of metagenomic data showed that genes for C1 metabolism occur at a high frequency in natural SAR11 populations. In short term incubations, natural communities of Sargasso Sea microbial plankton expressed a potential for the oxidation of ¹⁴C-labeled formate, formaldehyde, methanol and TMAO that was similar to cultured SAR11 cells and, like cultured SAR11 cells, incorporated a much larger percentage of pyruvate and glucose (27–35%) than of C1 compounds (2–6%) into biomass. Collectively, these genomic, cellular and environmental data show a surprising capacity for demethylation and C1 oxidation in SAR11 cultures and in natural microbial communities dominated by SAR11, and support the conclusion that C1 oxidation might be a significant conduit by which dissolved organic carbon is recycled to CO₂ in the upper ocean.