Evidence of high N2 fixation rates in the temperate northeast Atlantic

• Published in: Biogeosciences
• Main Authors: Fonseca-Batista, Debany, Li, Xuefeng, Riou, Virginie, Michotey, Valerie, Deman, Florian, Fripiat, François, Guasco, Sophie, Brion, Natacha, Lemaitre, Nolwenn, Tonnard, Manon, Gallinari, Morgane, Planquette, Hélène, Planchon, Frédéric, Sarthou, Géraldine, Elskens, Marc, Laroche, Julie, Chou, Lei, Dehairs, Frank
• Other Authors: Analytical, Environmental and Geo- Chemistry, Vrije Universiteit Brussel Bruxelles (VUB), Dalhousie University Halifax, Université libre de Bruxelles (ULB), 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 de MicrobiologiE de Géochimie et d'Ecologie Marines (LMGEM), Université de la Méditerranée - Aix-Marseille 2-Centre National de la Recherche Scientifique (CNRS), Max Planck Institute for Chemistry (MPIC), Max-Planck-Gesellschaft, 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), Institute of Geochemistry and Petrology ETH Zürich, Department of Earth Sciences Swiss Federal Institute of Technology - ETH Zürich (D-ERDW), Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich)-Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich), Institute for Marine and Antarctic Studies Hobart (IMAS), University of Tasmania Hobart, Australia (UTAS), ANR-13-BS06-0014,GEOVIDE,GEOVIDE, Une étude internationale GEOTRACES le long de la section OVIDE en Atlantique Nord et en Mer du Labrador(2013), ANR-11-LABX-0061,OTMed,Objectif Terre : Bassin Méditerranéen(2011), ANR-11-IDEX-0001,Amidex,INITIATIVE D'EXCELLENCE AIX MARSEILLE UNIVERSITE(2011)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: DINITROGEN-FIXATION; NITROGEN-FIXATION; ENVIRONMENTAL CONTROLS; DIAZOTROPHIC CYANOBACTERIA; MARINE; IRON; TRICHODESMIUM; ACL; VARIABILITY; DISTRIBUTIONS; NIFH GENES; [SDE.MCG]Environmental Sciences/Global Changes; [SDE]Environmental Sciences; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Northeast Atlantic
• Online Access: https://amu.hal.science/hal-02066554; https://amu.hal.science/hal-02066554/document; https://amu.hal.science/hal-02066554/file/bg-16-999-2019.pdf; https://doi.org/10.5194/bg-16-999-2019

International audience Diazotrophic activity and primary production (PP) were investigated along two transects (Belgica BG2014/14 and GEOVIDE cruises) off the western Iberian Margin and the Bay of Biscay in May 2014. Substantial N 2 fix-ation activity was observed at 8 of the 10 stations sampled , ranging overall from 81 to 384 µmol N m −2 d −1 (0.7 to 8.2 nmol N L −1 d −1), with two sites close to the Iberian Margin situated between 38.8 and 40.7 • N yielding rates reaching up to 1355 and 1533 µmol N m −2 d −1. Primary production was relatively lower along the Iberian Margin, with rates ranging from 33 to 59 mmol C m −2 d −1 , while it increased towards the northwest away from the peninsula, reaching as high as 135 mmol C m −2 d −1. In agreement with the area-averaged Chl a satellite data contemporaneous with our study period, our results revealed that post-bloom conditions prevailed at most sites, while at the northwestern-most station the bloom was still ongoing. When converted to carbon uptake using Redfield stoichiometry, N 2 fixation could support 1 % to 3 % of daily PP in the euphotic layer at most sites, except at the two most active sites where this contribution to daily PP could reach up to 25 %. At the two sites where N 2 fixation activity was the highest, the prymnesiophyte-symbiont Candidatus Atelocyanobac-terium thalassa (UCYN-A) dominated the nifH sequence pool, while the remaining recovered sequences belonged to non-cyanobacterial phylotypes. At all the other sites, however , the recovered nifH sequences were exclusively assigned phylogenetically to non-cyanobacterial phylotypes. The intense N 2 fixation activities recorded at the time of our study were likely promoted by the availability of phytoplankton-derived organic matter produced during the spring bloom, as evidenced by the significant surface particulate organic carbon concentrations. Also, the presence of excess phosphorus signature in surface waters seemed to contribute to sustaining N 2 fixation, particularly at the sites with ...