Patterns of nitrogen fixation along 10 N in the tropical Atlantic

[1] 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 mmol N*m *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.