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| Registros recuperados: 12 | |
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| Whitby, Hannah; Planquette, Helene; Cassar, Nicolas; Bucciarelli, Eva; Osburn, Christopher L.; Janssen, David J.; Cullen, Jay T.; González, Aridane G.; Völker, Christoph; Sarthou, Geraldine. |
| Primary production by phytoplankton represents a major pathway whereby atmospheric CO2 is sequestered in the ocean, but this requires iron, which is in scarce supply. As over 99% of iron is complexed to organic ligands, which increase iron solubility and microbial availability, understanding the processes governing ligand dynamics is of fundamental importance. Ligands within humic-like substances have long been considered important for iron complexation, but their role has never been explained in an oceanographically consistent manner. Here we show iron co-varying with electroactive humic substances at multiple open ocean sites, with the ratio of iron to humics increasing with depth. Our results agree with humic ligands composing a large fraction of the... |
| Tipo: Text |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00622/73388/72598.pdf |
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| Cassar, Nicolas; Tang, Weiyi; Gabathuler, Hans; Huang, Kuan. |
| Because of the difficulty in resolving the large variability of N2 fixation with current methods which rely on discrete sampling, the development of new methods for high resolution measurements is highly desirable. We present a new method for high-frequency measurements of aquatic N2 fixation by continuous flow-through incubations and spectral monitoring of the acetylene (C2H2, a substrate analog for N2) reduction to ethylene (C2H4). In this method, named “Flow-through incubation Acetylene Reduction Assays by Cavity ring-down laser Absorption Spectros-copy” (FARACAS), dissolved C2H2 is continuously admixed with seawater upstream of a continuous-flow stirred-tank reactor (CFSR) in which C2H2 reduction takes place. Downstream of the flow-through incubator,... |
| Tipo: Text |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00420/53139/54103.pdf |
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| Landwehr, Sebastian; Volpi, Michele; Haumann, F. Alexander; Robinson, Charlotte M; Thurnherr, Iris; Ferracci, Valerio; Baccarini, Andrea; Thomas, Jenny; Gorodetskaya, Irina; Tatzelt, Christian; Henning, Silvia; Modini, Rob L; Forrer, Heather J; Lin, Yajuan; Cassar, Nicolas; Simo, Rafel; Hassler, Christel; Moallemi, Alireza; Fawcett, Sarah E; Harris, Neil; Airs, Ruth; Derkani, Marzieh H; Alberello, Alberto; Toffoli, Alessandro; Chen, Gang; Rodríguez-ros, Pablo; Zamanillo, Marina; Cortés-greus, Pau; Xue, Lei; Bolas, Conor G; Leonard, Katherine C; Perez-cruz, Fernando; Walton, David; Schmale, Julia. |
| The Southern Ocean is a critical component of Earth’s climate system, but its remoteness makes it challenging to develop a holistic understanding of its processes from the small to the large scale. As a result, our knowledge of this vast region remains largely incomplete. The Antarctic Circumnavigation Expedition (ACE, austral summer 2016/2017) surveyed a large number of variables describing the dynamic state of the ocean and the atmosphere, the freshwater cycle, atmospheric chemistry, ocean biogeochemistry and microbiology. This circumpolar cruise included visits to twelve remote islands, the marginal ice zone, and the Antarctic coast. Here, we use 111 of the observed variables to study the latitudinal gradients, seasonality, shorter term variations, the... |
| Tipo: Text |
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| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00691/80275/83359.pdf |
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| Tang, Weiyi; Cassar, Nicolas. |
| Diazotrophs play a critical role in the biogeochemical cycling of nitrogen, carbon, and other elements in the global ocean. Despite their well‐recognized role, the diversity, abundance, and distribution of diazotrophs in the world's ocean remain poorly characterized largely due to limited observations. Here we update the database of diazotroph nifH gene abundances and assess how environmental factors may regulate diazotrophs at the global scale. Our meta‐analysis more than doubles the number of observations in the previous database. Using linear and nonlinear regressions, we find that the abundances of Trichodesmium, UCYN‐A, UCYN‐B, and Richelia relate differently to temperature, light, and nutrients. We further apply a random forest algorithm to estimate... |
| Tipo: Text |
Palavras-chave: Diazotrophs; Marine nitrogen fixation; Meta-analysis; Machine learning. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00591/70322/68359.pdf |
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| Gorsky, Gabriel; Bourdin, Guillaume; Lombard, Fabien; Pedrotti, Maria Luiza; Audrain, Samuel; Bin, Nicolas; Boss, Emmanuel; Bowler, Chris; Cassar, Nicolas; Caudan, Loic; Chabot, Genevieve; Cohen, Natalie R.; Cron, Daniel; De Vargas, Colomban; Dolan, John R.; Douville, Eric; Elineau, Amanda; Flores, J. Michel; Ghiglione, Jean Francois; Haentjens, Nils; Hertau, Martin; John, Seth G.; Kelly, Rachel L.; Koren, Ilan; Lin, Yajuan; Marie, Dominique; Moulin, Clementine; Moucherie, Yohann; Pesant, Stephane; Picheral, Marc; Poulain, Julie; Pujo-pay, Mireille; Reverdin, Gilles; Romac, Sarah; Sullivan, Mathew B.; Trainic, Miri; Tressol, Marc; Trouble, Romain; Vardi, Assaf; Voolstra, Christian R.; Wincker, Patrick; Agostini, Sylvain; Banaigs, Bernard; Boissin, Emilie; Forcioli, Didier; Furla, Paola; Galand, Pierre E.; Gilson, Eric; Reynaud, Stephanie; Sunagawa, Shinichi; Thomas, Olivier P.; Thurber, Rebecca Lisette Vega; Zoccola, Didier; Planes, Serge; Allemand, Denis; Karsenti, Eric; Planes, S.; Banaig, B.; Boissin, E.; Iwankow, G.; Allemand, D.; Zoccola, D.; Reynaud, S.; Beraud, E.; Djerbi, N.; Forcioli, D.; Furla, P.; Gilson, E.; Mcmind, R.; Ottaviani, A.; Rottinger, E.; Rouan, A.; Zamoum, T.; Flume, B. C. C.; Pogoreutz, C.; Voolstra, C. R.; Rothig, T.; Ziegler, M.; Paoli, L.; Ruscheweyh, H-j; Salazar, G.; Sunagawa, S.; Flores, J. M.; Koren, I; Trainic, M.; Lang-yona, N.; Vardi, A.; Conan, P.; Ghiglione, J-f; Pujo-pay, M.; Galand, P. E.; Hochart, C.; Audrain, S.; Bourgois, E.; Hertau, M.; Lancelot, J.; Monmarche, D.; Moulin, C.; Moucherie, Y.; Trouble, R.; Boss, E.; Bourdin, G.; Haentjens, N.; Karp-boss, L.; Douville, Eric; Agostini, S.; Mitsuhashi, G.; Kitano, Y.; Da Silva, O.; Dolan, J. R.; Gorsky, G.; Lemee, R.; Lombard, F.; Pedrotti, M-l; Cronin, D.; Sullivan, M.; Armstrong, E.; Aury, J-m; Barbe, V; Belser, C.; Carradec, Q.; Labadie, K.; Le-hoang, J.; Noel, B.; Poulain, J.; Wincker, P.; Klinges, G.; Vega-thunder, R.; Bonnival, E.; De Vargas, C.; Henry, N.; Marie, D.; Romac, S.; Pesant, S.; Miguel-gorda, M.; Thomas, O. P.; Bowler, C.; Friedrich, R.; Cassar, N.; Lin, Y.; John, S. G.; Kelly, R. L.; Cohen, N. R.; Reverdin, G.; Filee, J.. |
| Interactions between the ocean and the atmosphere occur at the air-sea interface through the transfer of momentum, heat, gases and particulate matter, and through the impact of the upper-ocean biology on the composition and radiative properties of this boundary layer. The Tara Pacific expedition, launched in May 2016 aboard the schooner Tara, was a 29-month exploration with the dual goals to study the ecology of reef ecosystems along ecological gradients in the Pacific Ocean and to assess inter-island and open ocean surface plankton and neuston community structures. In addition, key atmospheric properties were measured to study links between the two boundary layer properties. A major challenge for the open ocean sampling was the lack of ship-time available... |
| Tipo: Text |
Palavras-chave: Neuston/plankton genomics/taxonomy/imaging; Aerosols; NCP; IOP; Trace metals; Microplastic. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00599/71083/69390.pdf |
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| Wang, Seaver; Tang, Weiyi; Delage, Erwan; Gifford, Scott; Whitby, Hannah; González, Aridane G.; Eveillard, Damien; Planquette, Helene; Cassar, Nicolas. |
| Variation in the microbial cycling of nutrients and carbon in the ocean is an emergent property of complex planktonic communities. While recent findings have considerably expanded our understanding of the diversity and distribution of nitrogen (N2) fixing marine diazotrophs, knowledge gaps remain regarding ecological interactions between diazotrophs and other community members. Using quantitative 16S and 18S V4 rDNA amplicon sequencing, we surveyed eukaryotic and prokaryotic microbial communities from samples collected in August 2016 and 2017 across the Western North Atlantic. Leveraging and significantly expanding an earlier published 2015 molecular dataset, we examined microbial community structure and ecological co-occurrence relationships associated... |
| Tipo: Text |
Palavras-chave: Element cycles; Marine biology. |
| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00685/79677/82454.pdf |
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| Tang, Weiyi; Li, Zuchuan; Cassar, Nicolas. |
| Marine nitrogen (N2) fixation supplies “new” nitrogen to the global ocean, supporting uptake and sequestration of carbon. Despite its central role, marine N2 fixation and its controlling factors remain elusive. In this study, we compile over 1,100 published observations to identify the dominant predictors of marine N2 fixation and derive global estimates based on the machine learning algorithms of random forest (RF) and support vector regression (SVR). We find that no single environmental property predicts N2 fixation at global scales. Our RF and SVR algorithms, trained with sampling coordinates and month, solar radiation, wind speed, sea surface temperature, sea surface salinity, surface nitrate, surface phosphate, surface excess phosphorus, minimum... |
| Tipo: Text |
Palavras-chave: N-2 fixation; Machine-learning; Ocean. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00483/59501/62371.pdf |
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| Gu, Yuanyuan; Katul, Gabriel G.; Cassar, Nicolas. |
| The significance of the water-side gas transfer velocity for air–sea CO2 gas exchange (k) and its non-linear dependence on wind speed (U) is well accepted. What remains a subject of inquiry are biases associated with the form of the non-linear relation linking k to U (hereafter labeled as f(U), where f(.) stands for an arbitrary function of U), the distributional properties of U (treated as a random variable) along with other external factors influencing k, and the time-averaging period used to determine k from U. To address the latter issue, a Taylor series expansion is applied to separate f(U) into a term derived from time-averaging wind speed (labeled as ⟨U⟩, where ⟨.⟩ indicates averaging over a monthly time scale) as currently employed in climate... |
| Tipo: Text |
Palavras-chave: Carbon dioxide; Gas transfer velocity; Time-averaging; Wind speeds. |
| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00687/79949/82869.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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| Tang, Weiyi; Wang, Seaver; Fonseca-batista, Debany; Dehairs, Frank; Gifford, Scott; Gonzalez, Aridane G.; Gallinari, Morgane; Planquette, Helene; Sarthou, Geraldine; Cassar, Nicolas. |
| Marine N-2 fixation supports a significant portion of oceanic primary production by making N-2 bioavailable to planktonic communities, in the process influencing atmosphere-ocean carbon fluxes and our global climate. However, the geographical distribution and controlling factors of marine N-2 fixation remain elusive largely due to sparse observations. Here we present unprecedented high-resolution underway N-2 fixation estimates across over 6000 kilometers of the western North Atlantic. Unexpectedly, we find increasing N-2 fixation rates from the oligotrophic Sargasso Sea to North America coastal waters, driven primarily by cyanobacterial diazotrophs. N-2 fixation is best correlated to phosphorus availability and chlorophylla concentration. Globally,... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00484/59564/62548.pdf |
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| Lin, Yajuan; Cassar, Nicolas; Marchetti, Adrian; Moreno, Carly; Ducklow, Hugh; Li, Zuchuan. |
| Despite our current realization of the tremendous diversity that exists in plankton communities, we have little understanding of how this biodiversity influences the biological carbon pump other than broad paradigms such as diatoms contributing disproportionally to carbon export. Here we combine high-resolution underway O-2/Ar, which provides an estimate of net community production, with high-throughput 18 S ribosomal DNA sequencing to elucidate the relationship between eukaryotic plankton community structure and carbon export potential at the Western Antarctica Peninsula (WAP), a region which has experienced rapid warming and ecosystem changes. Our results show that in a diverse plankton system comprised of similar to 464 operational taxonomic units... |
| Tipo: Text |
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| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00409/52099/52810.pdf |
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| De Vaugelas, Jean; Meinesz, Alexandre; Antolic, Boris; Ballesteros, Enrique; Belsher, Thomas; Cassar, Nicolas; Ceccherelli, Giulia; Cinelli, Francesco; Cottalorda, Jean-michel; Orestano, Carla Fradà; Grau, Antoni; Jaklin, Andrej; Morucci, Carlo; Relini, Marco; Sandulli, Roberto; Span, Ante; Tripaldi, Giuseppe; Van Klaveren, Patrick; Zavodnik, Nevenka; Zuljevic, Ante. |
| Fourteen years after the first observation of Caulerpa taxifolia (Valh) C. Agardh in the northwestern Mediterranean Sea, this green alga of tropical origin is now present in five countries (Spain, France, Monaco, Italy and Croatia). By the end of 1997, more than 46 km(2), at depths of between 0 and 50 m, were found to be affected by this expansion. A standardization of the cartographic procedure is proposed here. Such a standardization is necessary to compare maps produced by various organizations from different countries. For a given independent station, it is based on the definition of three levels of colonization:Level I refers to a station where one or several colonies less than 100 m apart cover a total surface area inferior to 1000 m(2):Level II... |
| Tipo: Text |
Palavras-chave: Mediterranean Sea; Invasive species; Standardization; Caulerpa taxifolia; Cartography; Mer Méditerranée; Espèces envahissantes; Standardisation; Caulerpa taxifolia; Mediterranean Seacartographie. |
| Ano: 1999 |
URL: http://archimer.ifremer.fr/doc/1999/publication-837.pdf |
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| Registros recuperados: 12 | |
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