Trace metal biogeochemistry in the ocean: From chemical principles to biological complexity

In many oceanic regions, low concentrations of micronutrient trace metals exert strong control on phytoplankton growth, ecosystem structure, and carbon cycling. However, the task of linking trace metal concentrations with primary productivity is complicated by the interplay among physical, chemical, and biological processes. Paying tribute to the Morel et al. (2003) chapter from this series, we explore trace-metal phytoplankton interactions, with an emphasis on ocean-derived measurements and experiments. Specifically, we synthesize our current understanding on bioavailability of dissolved iron, trace metal accumulation in phytoplankton, and global (micro)nutrient limitation patterns, which are each underpinned by fundamental chemical and biological processes. We then showcase two microbial interactions that impact Fe biogeochemistry: (a) the two-way interactions between marine viruses and Fe that toggle Fe fate between regeneration for reuse by marine microbes and export to the deep ocean, and (b) the mineral-microbe interactions within colonies of the cyanobacteria Trichodesmium spp. that likely add “new” Fe from dust. We end with some directions and challenges in line with the multidisciplinary trajectory of trace metal biogeochemistry research.