Nitrogen fixation in the eastern Atlantic reaches similar levels in the Southern and Northern Hemisphere

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Fonseca-Batista, Debany, Dehairs, Frank, Riou, Virginie, Fripiat, François, Elskens, Marc, Deman, Florian, Brion, Natacha, Quéroué, Fabien, Bode, Maya, Auel, Holger
• Other Authors: Analytical, Environmental and Geo- Chemistry, Vrije Universiteit Brussel (VUB), Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Universität Bremen, ANR-11-IDEX-0001,Amidex,INITIATIVE D'EXCELLENCE AIX MARSEILLE UNIVERSITE(2011)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2017
• Subjects: ACL; Atlantic Ocean; benguela upwelling system; dinitrogen-fixation; dissolved organic nitrogen; fresh-water; iron availability; N-2 fixation; nitrogen fixation; oceanic fixed nitrogen; phytoplankton biomass; primary production; trichodesmium spp; tropical atlantic; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; North Atlantic
• Online Access: https://hal.univ-brest.fr/hal-01510348; https://hal.univ-brest.fr/hal-01510348/document; https://hal.univ-brest.fr/hal-01510348/file/Fonseca-Batista_etal_JoGR-O_2017.pdf; https://doi.org/10.1002/2016JC012335

WOS:000394996400035 International audience Euphotic layer dinitrogen (N-2) fixation and primary production (PP) were measured in the eastern Atlantic Ocean (38 degrees N-21 degrees S) using N-15(2) and C-13 bicarbonate tracer incubations. This region is influenced by Saharan dust deposition and waters with low nitrogen to phosphorus (N/P) ratios originating from the Subantarctic and the Benguela upwelling system. Depth-integrated rates of N-2 fixation in the north (0 degrees N-38 degrees N) ranged from 59 to 370 mu mol N m(-2) d(-1), with the maximal value at 19 degrees N under the influence of the northwest African upwelling. Diazotrophic activity in the south (0 degrees S-21 degrees S), though slightly lower, was surprisingly close to observations in the north, with values ranging from 47 to 119 mu mol N m(-2) d(-1). Our North Atlantic N-2 fixation rates correlate well with dust deposition, while those in the South Atlantic correlate strongly with excess phosphate relative to nitrate. There, the necessary iron is assumed to be supplied from the Benguela upwelling system. When converting N-2 fixation to carbon uptake using a Redfield ratio (6.6), we find that N-2 fixation may support up to 9% of PP in the subtropical North Atlantic (20 degrees N-38 degrees N), 5% in the tropical North Atlantic (0 degrees N-20 degrees N), and 1% of PP in the South Atlantic (0 degrees S-21 degrees S). Combining our data with published data sets, we estimate an annual N input of 27.610 Tg N yr(-1) over the open Atlantic Ocean, 11% of which enters the region between 20 degrees N and 50 degrees N, 71% between 20 degrees N and 10 degrees S, and 18% between 10 degrees N and 45 degrees S.