High variability of particulate organic carbon export along the North Atlantic GEOTRACES section GA01 as deduced from 234Th fluxes

• Published in: Biogeosciences
• Main Authors: Lemaitre, Nolwenn, Planchon, Frédéric, Planquette, Hélène, Dehairs, Frank, Fonseca-Batista, Debany, Roukaerts, Arnout, Deman, Florian, Tang, Yi, Mariez, Clarisse, Sarthou, Géraldine
• Other Authors: 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), Analytical, Environmental and Geo- Chemistry, Vrije Universiteit Brussel Bruxelles (VUB), Dalhousie University Halifax, School of Earth and Environmental Sciences Queens New York, Queens College New York, City University of New York New York (CUNY)-City University of New York New York (CUNY), 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-12-PDOC-0025,BITMAP,Biodisponibilité du fer et des métaux traces dans les particules marines(2012), ANR-10-LABX-0019,LabexMER,LabexMER Marine Excellence Research: a changing ocean(2010)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: PARTICLE EXPORT; COMMUNITY STRUCTURE; PHYTOPLANKTON PHYSIOLOGY; INVERSE RELATIONSHIP; SPATIAL VARIABILITY; SINKING VELOCITY; TWILIGHT ZONE; GLOBAL OCEAN; SEA; DISEQUILIBRIUM; ACL; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; Irminger Basin; North Atlantic
• Online Access: https://hal.science/hal-02322853; https://hal.science/hal-02322853/document; https://hal.science/hal-02322853/file/Lemaitre_etal_Biogeosciences_2018.pdf; https://doi.org/10.5194/bg-15-6417-2018

International audience In this study we report particulate organic carbon (POC) export fluxes for different biogeochemical basins in the North Atlantic as part of the GEOTRACES GA01 expedition (GEOVIDE, May-June 2014). Surface POC export fluxes were deduced by combining export fluxes of total Thorium-234 (Th-234) with the ratio of POC to Th-234 of sinking particles at the depth of export. Particles were collected in two size classes (> 53 and 1-53 mu m) using in situ pumps and the large size fraction was considered representative of sinking material. Surface POC export fluxes revealed latitudinal variations between provinces, ranging from 1.4 mmol m(-2) d(-1) in the Irminger basin, where the bloom was close to its maximum, to 12 mmol m(-2) d(-1) near the Iberian Margin, where the bloom had already declined. In addition to the state of progress of the bloom, variations of the POC export fluxes were also related to the phytoplankton size and community structure. In line with previous studies, the presence of coccolithophorids and diatoms appeared to enhance the POC export flux, while the dominance of picophytoplankton cells, such as cyanobacteria, resulted in lower fluxes. The ratio of POC export to primary production (PP) strongly varied regionally and was generally low (similar to 14 %), except at two stations located near the Iberian Margin (35 %) and within the Labrador basin (38 %), which were characterized by unusual low in situ PP. We thus conclude that during the GEOVIDE cruise, the North Atlantic was not as efficient in exporting carbon from the surface, as reported earlier by others. Finally, we also estimated the POC export at 100m below the surface export depth to investigate the POC transfer efficiencies. This parameter was also highly variable amongst regions, with the highest transfer efficiency at sites where coccolithophorids dominated.