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| Caffin, Mathieu; Berthelot, Hugo; Cornet-barthaux, Veronique; Barani, Aude; Bonnet, Sophie. |
| Biological dinitrogen (N2) fixation provides the major source of new nitrogen (N) to the open ocean, contributing more than atmospheric and riverine inputs to the N supply. Yet the fate of the diazotroph-derived N (DDN) in the planktonic food web is poorly understood due to technical limitations. The main goals of this study were to (i) quantify how much of DDN is released to the dissolved pool during N2 fixation and how much is transferred to bacteria, phytoplankton and zooplankton, (ii) to compare the DDN release and transfer efficiencies under contrasting N2 fixation activity and diversity the oligotrophic waters of the Western Tropical South Pacific (WTSP) Ocean. We used nanometer scale secondary ion mass spectrometry (nanoSIMS) coupled with 15N2... |
| Tipo: Text |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00419/53003/53951.pdf |
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| Irion, Solène; Christaki, Urania; Berthelot, Hugo; L’helguen, Stéphane; Jardillier, Ludwig. |
| Phytoplankton is composed of a broad-sized spectrum of phylogenetically diverse microorganisms. Assessing CO2-fixation intra- and inter-group variability is crucial in understanding how the carbon pump functions, as each group of phytoplankton may be characterized by diverse efficiencies in carbon fixation and export to the deep ocean. We measured the CO2-fixation of different groups of phytoplankton at the single-cell level around the naturally iron-fertilized Kerguelen plateau (Southern Ocean), known for intense diatoms blooms suspected to enhance CO2 sequestration. After the bloom, small cells (<20 µm) composed of phylogenetically distant taxa (prymnesiophytes, prasinophytes, and small diatoms) were growing faster (0.37 ± 0.13 and 0.22 ± 0.09... |
| Tipo: Text |
Palavras-chave: Biogeochemistry; Microbial ecology; Stable isotope analysis. |
| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00684/79595/82286.pdf |
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| Van Wambeke, France; Pfreundt, Ulrike; Barani, Aude; Berthelot, Hugo; Moutin, Thierry; Rodier, Martine; Hess, Wolfgang R.; Bonnet, Sophie. |
| Studies investigating the fate of diazotrophs through the microbial food web are lacking, although N2 fixation can fuel up to 50 % of new production in some oligotrophic oceans. In particular, the role played by heterotrophic prokaryotes in this transfer is largely unknown. In the frame of the VAHINE (VAriability of vertical and tropHIc transfer of diazotroph derived N in the south wEst Pacific) experiment, three replicate large-volume (∼ 50 m3) mesocosms were deployed for 23 days in the new Caledonia lagoon and were intentionally fertilized on day 4 with dissolved inorganic phosphorus (DIP) to stimulate N2 fixation. We specifically examined relationships between heterotrophic bacterial production (BP) and N2 fixation or primary production, determined... |
| Tipo: Text |
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| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00342/45331/44792.pdf |
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| Caffin, Mathieu; Moutin, Thierry; Foster, Rachel Ann; Bouruet-aubertot, Pascale; Doglioli, Andrea Michelangelo; Berthelot, Hugo; Guieu, Cecile; Grosso, Olivier; Helias-nunige, Sandra; Leblond, Nathalie; Gimenez, Audrey; Petrenko, Anne Alexandra; De Verneil, Alain; Bonnet, Sophie. |
| We performed nitrogen (N) budgets in the photic layer of three contrasting stations representing different trophic conditions in the western tropical South Pacific (WTSP) Ocean during austral summer conditions (February–March 2015). Using a Lagrangian strategy, we sampled the same water mass for the entire duration of each long-duration (5 days) station, allowing us to consider only vertical exchanges for the budgets. We quantified all major vertical N fluxes both entering (N2 fixation, nitrate turbulent diffusion, atmospheric deposition) and leaving the photic layer (particulate N export). The three stations were characterized by a strong nitracline and contrasted deep chlorophyll maximum depths, which were lower in the oligotrophic Melanesian archipelago... |
| Tipo: Text |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00439/55074/56503.pdf |
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| Ganachaud, Alexandre; Cravatte, Sophie; Sprintall, Janet; Germineaud, Cyril; Alberty, Marion; Jeandel, Catherine; Eldin, Gerard; Metzl, Nicolas; Bonnet, Sophie; Benavides, Mar; Heimburger, Lars-eric; Lefevre, Jerome; Michael, Susanna; Resing, Joseph; Queroue, Fabien; Sarthou, Geraldine; Rodier, Martine; Berthelot, Hugo; Baurand, Francois; Grelet, Jacques; Hasegawa, Takuya; Kessler, William; Kilepak, Moyep; Lacan, Francois; Privat, Emilien; Send, Uwe; Van Beek, Pieter; Souhaut, Marc; Sonke, Jeroen E.. |
| The semi-enclosed Solomon Sea in the southwestern tropical Pacific is on the pathway of a major oceanic circuit connecting the subtropics to the equator via energetic western boundary currents. Waters transiting through this area replenish the Pacific Warm Pool and ultimately feed the equatorial current system, in particular the equatorial undercurrent. In addition to dynamical transformations, water masses undergo nutrient and micronutrient enrichment when coming in contact with the coasts, impacting the productivity of the downstream equatorial region. Broadscale observing systems are not well suited for describing the fine-scale currents and water masses properties in the Solomon Sea, leaving it relatively unexplored. Two multidisciplinary oceanographic... |
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| Ano: 2017 |
URL: https://archimer.ifremer.fr/doc/00390/50185/50808.pdf |
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| Bonnet, Sophie; Berthelot, Hugo; Turk-kubo, Kendra; Fawcett, Sarah; Rahav, Eyal; L'Helguen, Stephane; Berman-frank, Ilana. |
| N2 fixation rates were measured daily in large (∼ 50 m3) mesocosms deployed in the tropical southwest Pacific coastal ocean (New Caledonia) to investigate the temporal variability in N2 fixation rates in relation with environmental parameters and study the fate of diazotroph-derived nitrogen (DDN) in a low-nutrient, low-chlorophyll ecosystem. The mesocosms were fertilized with ∼ 0.8 µM dissolved inorganic phosphorus (DIP) to stimulate diazotrophy. Bulk N2 fixation rates were replicable between the three mesocosms, averaged 18.5 ± 1.1 nmol N L−1 d−1 over the 23 days, and increased by a factor of 2 during the second half of the experiment (days 15 to 23) to reach 27.3 ± 1.0 nmol N L−1 d−1. These later rates measured after the DIP fertilization are higher... |
| Tipo: Text |
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| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00333/44459/44136.pdf |
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| Bonnet, Sophie; Caffin, Mathieu; Berthelot, Hugo; Grosso, Olivier; Benavides, Mar; Helias-nunige, Sandra; Guieu, Cecile; Stenegren, Marcus; Foster, Rachel Ann. |
| Here we report N2 fixation rates from a ∼ 4000km transect in the western and central tropical South Pacific, a particularly undersampled region in the world ocean. Water samples were collected in the euphotic layer along a west to east transect from 160°E to 160°W that covered contrasting trophic regimes, from oligotrophy in the Melanesian archipelago (MA) waters to ultra-oligotrophy in the South Pacific Gyre (GY) waters. N2 fixation was detected at all 17 sampled stations with an average depth-integrated rate of 631±286µmol N m−2 d−1 (range 196–1153µmol N m−2 d−1) in MA waters and of 85±79µmol N m−2 d−1 (range 18–172µmol N m−2 d−1) in GY waters. Two cyanobacteria, the larger colonial filamentous Trichodesmium and the smaller UCYN-B, dominated the... |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00419/53049/53987.pdf |
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| Berthelot, Hugo; Duhamel, Solange; L’helguen, Stéphane; Maguer, Jean-francois; Wang, Seaver; Cetinić, Ivona; Cassar, Nicolas. |
| Nitrogen (N) is a limiting nutrient in vast regions of the world’s oceans, yet the sources of N available to various phytoplankton groups remain poorly understood. In this study, we investigated inorganic carbon (C) fixation rates and nitrate (NO3−), ammonium (NH4+) and urea uptake rates at the single cell level in photosynthetic pico-eukaryotes (PPE) and the cyanobacteria Prochlorococcus and Synechococcus. To that end, we used dual 15N and 13C-labeled incubation assays coupled to flow cytometry cell sorting and nanoSIMS analysis on samples collected in the North Pacific Subtropical Gyre (NPSG) and in the California Current System (CCS). Based on these analyses, we found that photosynthetic growth rates (based on C fixation) of PPE were higher in the CCS... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00462/57383/64185.pdf |
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