Distribution and rates of nitrogen fixation in the western tropical South Pacific Ocean constrained by nitrogen isotope budgets

• Published in: Biogeosciences
• Main Authors: Knapp, Angela, Mccabe, Kelly, Grosso, Olivier, Leblond, Nathalie, Moutin, Thierry, Bonnet, Sophie
• Other Authors: Florida State University Tallahassee (FSU), 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 d'océanographie de Villefranche (LOV), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de la Mer de Villefranche (IMEV), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; Pacific; North Atlantic
• Online Access: https://hal.science/hal-01790780; https://hal.science/hal-01790780/document; https://hal.science/hal-01790780/file/Knapp_et_al_BG_2018.pdf; https://doi.org/10.5194/bg-15-2619-2018

International audience Constraining the rates and spatial distribution of dinitrogen (N 2) fixation fluxes to the ocean informs our understanding of the environmental sensitivities of N 2 fixa-tion as well as the timescale over which the fluxes of nitrogen (N) to and from the ocean may respond to each other. Here we quantify rates of N 2 fixation as well as its contribution to export production along a zonal transect in the western tropical South Pacific (WTSP) Ocean using N isotope (" δ 15 N ") budgets. Comparing measurements of water column nitrate + nitrite δ 15 N with the δ 15 N of sinking particulate N at a western, central, and eastern station, these δ 15 N budgets indicate high, modest, and low rates of N 2 fixation at the respective stations. The results also imply that N 2 fixation supports exceptionally high, i.e. ≥ 50 %, of export production at the western and central stations, which are also prox-imal to the largest iron sources. These geochemically based rates of N 2 fixation are equal to or greater than those previously reported in the tropical North Atlantic, indicating that the WTSP Ocean has the capacity to support globally significant rates of N 2 fixation, which may compensate for N removal in the oxygen-deficient zones of the eastern tropical Pacific.