Particulate barium tracing of significant mesopelagic carbon remineralisation in the North Atlantic

• Published in: Biogeosciences
• Main Authors: Lemaitre, Nolwenn, Planquette, Hélène, Planchon, Frédéric, Sarthou, Géraldine, Jacquet, Stéphanie, García-Ibáñez, Maribel, Gourain, Arthur, Cheize, Marie, Monin, Laurence, André, Luc, Laha, Priya, Terryn, Herman, Dehairs, Frank
• 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), Analytical, Environmental and Geo- Chemistry, Vrije Universiteit Brussel Bruxelles (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), Bjerknes Centre for Climate Research (BCCR), Department of Biological Sciences Bergen (BIO / UiB), University of Bergen (UiB)-University of Bergen (UiB), Consejo Superior de Investigaciones Cientificas España = Spanish National Research Council Spain (CSIC), Department of Earth Ocean and Ecological Sciences Liverpool, University of Liverpool, Royal Museum for Central Africa Tervuren (RMCA), 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: Sinking particles; Remineralisation; Mesopelagic; North Atlantic; Biological carbon pump; ACL; [SDE]Environmental Sciences; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Labrador Sea
• Online Access: https://amu.hal.science/hal-02024247; https://amu.hal.science/hal-02024247/document; https://amu.hal.science/hal-02024247/file/bg-15-2289-2018.pdf; https://doi.org/10.5194/bg-15-2289-2018

International audience The remineralisation of sinking particles by prokaryotic heterotrophic activity is important for controlling oceanic carbon sequestration. Here, we report mesopelagic particulate organic carbon (POC) remineralisation fluxes in the North Atlantic along the GEOTRACES-GA01 section (GEOVIDE cruise; May-June 2014) using the particulate biogenic barium (excess barium; Ba xs) proxy. Important mesopelagic (100-1000 m) Ba xs differences were observed along the transect depending on the intensity of past blooms, the phytoplankton community structure, and the physical forcing, including downwelling. The subpolar province was characterized by the highest mesopelagic Ba xs content (up to 727 pmol L −1), which was attributed to an intense bloom averaging 6 mg chl a m −3 between January and June 2014 and by an intense 1500 m deep convection in the central Labrador Sea during the winter preceding the sampling. This down-welling could have promoted a deepening of the prokaryotic heterotrophic activity, increasing the Ba xs content. In comparison , the temperate province, characterized by the lowest Ba xs content (391 pmol L −1), was sampled during the bloom period and phytoplankton appear to be dominated by small and calcifying species, such as coccolithophorids. The Ba xs content, related to oxygen consumption, was converted into a remineralisation flux using an updated relationship, proposed for the first time in the North Atlantic. The estimated fluxes were of the same order of magnitude as other fluxes obtained using independent methods (moored sediment traps, incubations) in the North Atlantic. Interestingly, in the subpolar and subtropical provinces, mesopelagic POC remineralisa-tion fluxes (up to 13 and 4.6 mmol C m −2 d −1 , respectively) were equalling and occasionally even exceeding upper-ocean POC export fluxes, deduced using the 234 Th method. These results highlight the important impact of the mesopelagic remineralisation on the biological carbon pump of the studied area with a near-zero, ...