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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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| 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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| 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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| 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,... |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00484/59564/62548.pdf |
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