On the Role of the Amazon River for N ₂ Fixation in the Western Tropical Atlantic

The high rates of N2 fixation observed in the Western Tropical Atlantic Ocean are powered, at least parts, by large influx nutrients from Amazon River. To disentangle impact on different factors controlling region, we use a high-resolution regional model (Regional Oceanic Modeling System-Biogeochemical Elemental Cycling model) that includes two diazotrophic phytoplankton classes (Trichodesmium and Diatom-Diazotroph-Assemblages, DDAs). In our simulations, enhances marine 74% (3.8 Tg N yr−1), with most enhancement driven DDAs represent 90% community plume waters. determine how creates conditions which thrive, analyze bottom-up top-down controls along pathway competition is disrupted delivery river. Along entire pathway, out-compete Trichodesmium as their higher maximum growth makes them more efficient building biomass. Nevertheless, never account for than 25% total biomass they face other non-diazotrophic types riverine nutrients. Overall, thrive offshore region where nutrient uptake advantages (N-fixation, DOP uptake) concomitant relaxed grazing pressure.