Nitrogen fixation across scales

Abstract: The availability of reactive nitrogen limits primary production in much of the global ocean surface. Diazotrophs are small microbes (~1 to 200 µm) capable of fixing atmospheric dinitrogen (N₂), reducing it to ammonium and dissolved organic nitrogen forms. Despite their small size, their impact becomes global as they fertilize vast oligotrophic regions and control the nitrogen reservoir of the ocean. As other marine microbes, diazotrophs depend on a dynamic mosaicof environmental factors such as light, temperature and nutrients that vary across complex spatio-temporal scales. Our understanding of each of these factors is provided by different disciplines (e.g. physical oceanography, genetics or organic geochemistry). Hence, understanding how diazotrophs transit across scales needs a transdisciplinary approachcapable of integrating several disciplines. In this talk we will explore the scales that drive oceanic N₂ fixation, from cell-to-molecule interactions, through mesoscale and regional level distributions up to global contributions to the nitrogen budget.