Patterns of nitrogen fixation along 10°N in the tropical Atlantic

Nitrogen fixation supports new production in the oligotrophic oceans and removes dinitrogen and carbon dioxide from mixed layer waters. N‐fixation rates have been estimated in various ways but measurements are still too rare and factors limiting N‐fixation are not yet fully understood. Here we present data from a transect along 10°N through the tropical Atlantic on the Meteor Cruise 55 where N‐fixation rates between 3.7 and 255 μmol N*m−2*d−1 were recorded. The highest rates occurred off Africa in the eastern tropical North Atlantic (ETNA), and in the Amazon River plume in the West and contributed to 1–12.2% of the N‐demand of primary production. N‐fixation rates correlated with dissolved Fe concentrations, which were 20–280 times greater than the estimated demand. High atmospheric Fe inputs combined with the shallow nutricline make the ETNA a favourable environment for N‐fixers