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, with implications for ocean carbon sequestration, but 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 of phytoplankton species spanning across different functional groups with a novel set of approaches that combined data synthesis and diagnostic modelling. Our analysis reinforces the importance of Fe, showing that representative species of diatoms, picocyanobacteria, and dinoflagellates are Fe limited in about 60%, 38%, and 5% of the global ocean. However, diatoms are also Mn limited in ~20% and dinoflagellates Zn limited in over 60% of the ocean. Our analyses additionally highlight a previously overlooked role of Cu in limiting the growth of phytoplankton and suggest that trace metal supply may have a greater impact on the distribution of diatoms and dinoflagellates than on coccolithophores. The inferred patterns of trace metal limitation for different phytoplankton are broadly supported by transcriptomic data from surface ocean. Using projections of how trace metal concentrations may evolve with climate change, we show that the future oceans may promote widespread Zn limitation, shifting phytoplankton communities to groups that drive a weaker biological pump.