Phytoplankton transform inorganic carbon into thousands of biomolecules that represent an important pool of fixed carbon, nitrogen, and sulfur in the surface ocean. Metabolite production differs between phytoplankton, and the flux of these molecules through the microbial food web depends on compound-specific bioavailability to members of a wider microbial community. Yet relatively little is known about the diversity or concentration of metabolites within marine plankton. Here we compare 313 polar metabolites in 21 cultured phytoplankton species and in natural planktonic communities across environmental gradients to show that bulk community metabolomes reflect chemical composition of the phytoplankton community. We also show that groups of compounds have similar patterns across space and taxonomy suggesting that the concentrations of these compounds in the environment are controlled by similar sources and sinks. We quantify several compounds in the surface ocean that represent substantial understudied pools of labile carbon. For example, the N-containing metabolite homarine was up to 3% of particulate carbon and is produced in high concentrations by cultured Synechococcus, and S-containing gonyol accumulated up to 2.5 nM in surface particles and likely originates from dinoflagellates or haptophytes. Our results show that phytoplankton composition directly shapes the carbon composition of the surface ocean. Our findings suggest that in order to access these pools of bioavailable carbon, the wider microbial community must be adapted to phytoplankton community composition.

All methods for data collection, generation and data processing are found with associated preprint Heal et al "Marine community metabolomes carry fingerprints of phytoplankton community composition" on bioRxiv (doi: https://doi.org/10.1101/2020.12.22.424086).

These data are supplemental tables 4-11 associated with the preprint for Heal et al "Marine community metabolomes carry fingerprints of phytoplankton community composition" on bioRxiv (doi: https://doi.org/10.1101/2020.12.22.424086), as described in the preprint and below.