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

Type Article
Date 2018-04
Language English
Author(s) Lemaitre Nolwenn1, 2, 9, Planquette Helene1, Planchon FredericORCID1, Sarthou Geraldine1, Jacquet Stephanie3, Garcia-Ibanez Maria IsabelORCID4, 5, Gourain ArthurORCID1, 6, Cheize Marie1, Monin Laurence7, Andre Luc7, Laha Priya8, Terryn Herman8, Dehairs Frank2
Affiliation(s) 1 : IUEM, UMR 6539, Lab Sci Environm Marin LEMAR, Technopole Brest Iroise, F-29280 Plouzane, France.
2 : Vrije Univ Brussel, Analyt Environm & Geochem, Earth Syst Sci Res Grp, Brussels, Belgium.
3 : Aix Marseille Univ, CNRS INSU, Univ Toulon, IRD,MIO,UM110, F-13288 Marseille, France.
4 : Bjerknes Ctr Climate Res, Uni Res Climate, N-5008 Bergen, Norway.
5 : IIM CSIC, Inst Invest Marinas, Eduardo Cabello 6, Vigo 36208, Spain.
6 : Univ Liverpool, Sch Environm Sci, Ocean Sci Dept, Liverpool L69 3GP, Merseyside, England.
7 : Royal Museum Cent Africa, Earth Sci Dept, Leuvensesteenweg 13, B-3080 Tervuren, Belgium.
8 : Vrije Univ Brussel, Dept Mat & Chem, SURF Res Grp, Brussels, Belgium.
9 : ETH, Inst Geochem & Petr, Dept Earth Sci, Zurich, Switzerland.
Source Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2018-04 , Vol. 15 , N. 8 , P. 2289-2307
DOI 10.5194/bg-15-2289-2018
WOS© Times Cited 15
Note Special issue GEOVIDE, an international GEOTRACES study along the OVIDE section in the North Atlantic and in the Labrador Sea (GA01) Editor(s): G. Henderson, M. Lohan, L. Bopp, C. Jeandel, and G. Reverdin
Abstract

The remineralisation of sinking particles by prokaryotic heterotrophic activities 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; Baxs) proxy. Important mesopelagic (100–1000 m) Baxs 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 Baxs 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 downwelling could have promoted a deepening of the prokaryotic heterotrophic activity, increasing the Baxs content. In comparison, the temperate province, characterized by the lowest Baxs 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 Baxs content, related to an 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 in the same order of magnitude than other fluxes obtained by independent methods (moored sediment traps, incubations) in the North Atlantic. Interestingly, in the subpolar and subtropical provinces, mesopelagic POC remineralisation 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, highlighting the important impact of the mesopelagic remineralisation on the biological carbon pump with a near-zero, deep (> 1000 m) carbon sequestration efficiency in spring 2014.

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Lemaitre Nolwenn, Planquette Helene, Planchon Frederic, Sarthou Geraldine, Jacquet Stephanie, Garcia-Ibanez Maria Isabel, Gourain Arthur, Cheize Marie, Monin Laurence, Andre Luc, Laha Priya, Terryn Herman, Dehairs Frank (2018). Particulate barium tracing of significant mesopelagic carbon remineralisation in the North Atlantic. Biogeosciences, 15(8), 2289-2307. Publisher's official version : https://doi.org/10.5194/bg-15-2289-2018 , Open Access version : https://archimer.ifremer.fr/doc/00412/52308/