Diverse assimilation pathways drive carbon fixation in the global ocean

How do the ocean’s most abundant microbes regulate Earth’s primary carbon sink? Most investigations of microbial carbon fixation remain regionally focused or limited to single pathways, obscuring global patterns in the biosphere’s largest habitat. Here, we compile and analyze global metagenomic, transcriptomic, and proteomic data to map the in situ activity of all major inorganic carbon assimilation pathways—from photo- and chemo-autotrophy to anaplerotism—across marine ecosystems. Our meta-analysis reveals a high diversity of active pathways across regions and depths, with microbial communities operating along a continuous metabolic carbon assimilation spectrum. Lineages occupy conserved positions on this spectrum, and the spectrum’s balance is predictable from environmental gradients. Together, our results identify the main drivers of ocean carbon fixation, the widespread nature of these pathways, their taxonomic carriers, niche partitioning, and environmental controls, directly linking microbial carbon assimilation strategies to ocean biogeochemistry and climate sensitivity