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| Llopis Monferrer, Natalia; Leynaert, Aude; Tréguer, Paul; Gutiérrez‐rodríguez, Andrés; Moriceau, Brivaela; Gallinari, Morgane; Latasa, Mikel; L'Helguen, Stéphane; Maguer, Jean-francois; Safi, Karl; Pinkerton, Matthew H.; Not, Fabrice. |
| We examined biogenic silica production and elementary composition (biogenic Si, particulate organic carbon and particulate organic nitrogen) of Rhizaria and diatoms in the upper 200 m along a transect in the Southwest Pacific sector of the Southern Ocean during austral summer (January–February 2019). From incubations using the 32Si radioisotope, silicic acid uptake rates were measured at 15 stations distributed in the Polar Front Zone, the Southern Antarctic Circumpolar Current and the Ross Sea Gyre. Rhizaria cells are heavily silicified (up to 7.6 nmol Si cell−1), displaying higher biogenic Si content than similar size specimens found in other areas of the global ocean, suggesting a higher degree of silicification of these organisms in the silicic acid... |
| Tipo: Text |
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| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00692/80407/83515.pdf |
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| L'Helguen, Stéphane; Rimmelin-maury, Peggy; Repecaud, Michel; Quemener, Loic; Beaumont, L.; Grosssteffan, Emilie; Tréguer, Paul; Bozec, Yann. |
| Les écosystèmes côtiers sont soumis à de multiples forçages physiques et chimiques qui agissent à des échelles de temps très différentes. Pour décrire et prédire l’impact de ces forçages sur les écosystèmes, il est impératif de mesurer à long terme les caractéristiques physiques, chimiques et biologiques des eaux côtières. Depuis plus de 15 ans, un partenariat réunit l’IUEM/UBO, l’IFREMER et l'INSU pour assurer le suivi régulier et à long terme de la physico-chimie des eaux côtières à l’interface de la rade de Brest et de la mer d’Iroise (site de Ste Anne du Portzic, 48°21’60 N, 4°33’04 W ). Ce suivi repose sur une stratégie combinée de mesures à basse fréquence (série SOMLIT-Brest - Service d’Observation en Milieu LITtoral) et de mesures à haute fréquence... |
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| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00628/73967/73326.pdf |
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| Ridame, Celine; Le Moal, Marc; Guieu, Cecile; Ternon, E.; Biegala, I.c.; L'Helguen, Stéphane; Pujo-pay, M.. |
| A better understanding of the factors controlling N2 fixation is a pre-requisite for improving our knowledge on the contribution of N2 fixation process in the nitrogen cycling. Trace-metal clean nutrient/dust addition bioassays (+P, +PFe, +dust) were performed at three stations located in the western, central and eastern Mediterranean Sea, in summer 2008 as part of the BOUM cruise. The main goals were (1) to investigate the nutrient factor(s) limiting N2 fixation (uptake of 15N2) and (2) to evaluate the potential impact of a Saharan dust event on this biological process during the stratification period. Initially, surface waters at the three stations were DIP-depleted (<10 nM) while the DFe concentrations were relatively high (from 1.2 to 2.3 nM) most... |
| Tipo: Text |
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| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00133/24410/22403.pdf |
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| Mansour, Joost Samir; Norlin, Andreas; Llopis Monferrer, Natalia; L'Helguen, Stéphane; Not, Fabrice. |
| Rhizaria are large protistan cells that have been shown to be a major component of the planktic community in the oceans and contribute significantly to major biogeochemical cycles such as carbon or silicon. However, unlike for many other protists, limited data is available on rhizarian cellular carbon (C) and nitrogen (N) content and cell volume. Here we present novel C and N mass to volume equations and ratios for nine Rhizaria taxa belonging to Radiolaria (i.e., Collozoum, Sphaerozoum, Collosphaeridae, Acantharia, Nassellaria, and Spumellaria) and Phaeodaria (i.e., Aulacantha, Protocystis, and Challengeria). The C and N content of collodarian cells was significantly correlated to cell volume as expressed by the mass : vol equations ng C cell−1 =... |
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| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00684/79596/82288.pdf |
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| Giraud, Mélanie; Garçon, Véronique; De La Broise, Denis; L'Helguen, Stéphane; Sudre, Joël; Boye, Marie. |
| Installation of an Ocean Thermal Energy Conversion pilot plant (OTEC) off the Caribbean coast of Martinique is expected to use approximately 100,000 m3 h−1 of deep seawater for its functioning. This study examined the potential effects of the cold nutrient-rich deep seawater discharge on the phytoplankton community living in the surface warm oligotrophic waters before the installation of the pilot plant. Numerical simulations of deep seawater upwelled by the OTEC, showed that a 3.0 °C temperature change, considered as a critical threshold for temperature impact, was never reached during an annual cycle on the top 150 m of the water column on two considered sections centered on the OTEC. The thermal effect should be limited, <1 km2 on the area exhibited... |
| Tipo: Text |
Palavras-chave: Marine microbial ecosystem; Biogeochemistry; Modeling; Artificial seawater discharge in situ experiments; Environmental standards. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00507/61867/65935.pdf |
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| L'Helguen, Stéphane. |
| Des quantités très importantes d'azote à la fois minéral (nitrate, nitrite, ammonium) et organique (dissous et particulaire) sont déversées par la Seine dans les eaux côtières. Ces apports peuvent modifier de manière importante le fonctionnement des écosystèmes pélagique et benthique en Baie de Seine. Ils peuvent, en particulier, en enrichissant le milieu en azote, intensifier les processus d'absorption du phytoplancton et déclencher des proliférations algales. La matière organique ainsi produite et la matière organique directement importée dans le système peuvent accroître fortement les processus de régénération dans la colonne d'eau. Les apports d'azote minéral peuvent, par ailleurs, lorsqu'ils s'effectuent sous la forme d'ammonium (rejets urbains ou... |
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| Ano: 1996 |
URL: http://archimer.ifremer.fr/doc/00104/21490/19071.pdf |
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