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| Messié, M.; Petrenko, A.; Doglioli, A.m.; Aldebert, C.; Martinez, Elodie; Koenig, G.; Bonnet, S.; Moutin, T.. |
| In oligotrophic gyres of the tropical ocean, islands can enhance phytoplankton biomass and create hotspots of productivity and biodiversity. This “Island Mass Effect” (IME) is typically identified by increased chlorophyll concentrations next to an island. Here we use a simple plankton model in a Lagrangian framework to represent an unexplained open ocean bloom, demonstrating how islands could have triggered it remotely. This new type of IME, termed “delayed IME”, occurs when nitrate is limiting, N:P ratios are low, and excess phosphate and iron remain in water masses after an initial bloom associated to a “classical” IME. Nitrogen fixers then slowly utilize leftover phosphate and iron while water masses get advected away, resulting in a bloom decoupled in... |
| Tipo: Text |
Palavras-chave: Island mass effect; Lagrangian analysis; Nitrogen fixation; Nutrient supply; Oligotrophic ocean; Phytoplankton bloom. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00600/71162/69489.pdf |
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| Bonnet, S.; Grosso, O.; Moutin, T.. |
| This study provides extensive data on planktonic N(2) fixation rates across the whole Mediterranean Sea. They show that N(2) fixation occurs in Mediterranean waters during the stratification period, with a clear decreasing trend from the oligotrophic western basin (10-76 mu mol m(-2) d(-1)) to the ultra oligotrophic eastern basin (0-0.4 mu mol m(-2) d(-1)). Highest rates are measured in the less oligotrophic western basin, between the surface and 75 m-depth, where 45 to 75% of N(2) fixation are found within the picoplanktonic fraction (<3 mu m). While the biogeochemical impact of N(2) fixation in the eastern basin seems negligible, N(2) fixation is able to sustain up to 35% of new primary production during the stratified period in the western basin.... |
| Tipo: Text |
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| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00133/24389/22423.pdf |
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| Berthelot, H; Moutin, T.; L'Helguen, S.; Leblanc, K.; Helias, S.; Grosso, O.; Leblond, N.; Charriere, B.; Bonnet, S.. |
| In the oligotrophic ocean characterized by nitrate (NO3-) depletion in surface waters, dinitrogen (N-2) fixation and dissolved organic nitrogen (DON) can represent significant nitrogen (N) sources for the ecosystem. In this study, we deployed large in situ mesocosms in New Caledonia in order to investigate (1) the contribution of N-2 fixation and DON use to primary production (PP) and particle export and (2) the fate of the freshly produced particulate organic N (PON), i.e., whether it is preferentially accumulated and recycled in the water column or exported out of the system. The mesocosms were fertilized with phosphate (PO43-) in order to prevent phosphorus (P) limitation and promote N-2 fixation. The diazotrophic community was dominated by... |
| Tipo: Text |
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| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00275/38672/73173.pdf |
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| Berthelot, H.; Benavides, M.; Moisander, P. H.; Grosso, O.; Bonnet, S.. |
| Dinitrogen (N-2) fixation rates were investigated in the euphotic layer of the Bismarck and Solomon Seas using N-15(2) incubation assays taking into account both the particulate and the dissolved pools. Average depth-integrated particulate N-2 fixation rates were 203 (range 43-399) and 1396 (range 176-3132)mol N m(-2) d(-1) in the Bismarck and Solomon Seas, respectively. In both seas, N-2 fixation measured in the dissolved pool was similar to particulate N-2 fixation, highlighting the potentially substantial underestimation of N-2 fixation in oceanic budgets when only particulate N-2 fixation is considered. Among the diazotroph phylotypes targeted using quantitative polymerase chain reaction amplification of nifH genes, Trichodesmium was the most abundant.... |
| Tipo: Text |
Palavras-chave: Diazotrophy; Trichodesmium; Crocosphaera; Cyanothece; N release. |
| Ano: 2017 |
URL: https://archimer.ifremer.fr/doc/00404/51512/72629.pdf |
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| Ridame, C.; Dekaezemacker, J.; Guieu, C.; Bonnet, S.; L'Helguen, S.; Malien, F.. |
| The response of the phytoplanktonic community (primary production and algal biomass) to contrasted Saharan dust events (wet and dry deposition) was studied in the framework of the DUNE ("a DUst experiment in a low-Nutrient, low-chlorophyll Ecosystem") project. We simulated realistic dust deposition events (10 gm(-2)) into large mesocosms (52m(3)). Three distinct dust addition experiments were conducted in June 2008 (DUNE-1-P: simulation of a wet deposition; DUNE-1-Q: simulation of a dry deposition) and 2010 (DUNE-2-R1 and DUNE-2-R2: simulation of two successive wet depositions) in the northwestern oligotrophic Mediterranean Sea. No changes in primary production (PP) and chlorophyll a concentrations (Chl a) were observed after a dry deposition event, while... |
| Tipo: Text |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00216/32741/31144.pdf |
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