Exploring Global Patterns of Trace Metal Limitation as a Regulator of the Distribution of Dominant Marine Phytoplankton Groups

ABSTRACT The availability of essential elements determines the productivity of phytoplankton and regulates ocean carbon sequestration. The role of multiple trace metals for driving the biogeography of key phytoplankton groups that are major components of the carbon pump is not well understood. We explore the patterns of trace metal limitation on phytoplankton growth, spanning across different functional groups by uniting a compilation of decades of laboratory culture experiments, via diagnostic modelling, with emerging global‐scale datasets of ocean trace metal content and genomics. Our analysis reinforces the importance of Fe, showing that representative species of diatoms and picocyanobacteria may be Fe limited in about 60% and 38% of the global ocean. Diatoms are also Mn limited in ~20% of the ocean. An autotrophic dinoflagellate may be Zn limited in over 60% of the ocean. The levels of limitation are highly controlled by the bioavailability of trace metals. Our analyses additionally highlight that trace metal supply may have a greater impact on the distribution of diatoms than on coccolithophores. The inferred patterns of trace metal limitation for different phytoplankton are broadly supported by transcriptomic data from the surface ocean. Using projections of how trace metal concentrations may evolve with climate change, we show that future oceans may promote widespread Zn limitation, shifting phytoplankton communities to groups that drive a weaker biological pump.