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| Spungin, Dina; Belkin, Natalia; Foster, Rachel; Stenegren, Marcus; Caputo, Andrea; Pujo-pay, Mireille; Leblond, Nathalie; Dupouy, Cecile; Bonnet, Sophie; Berman-frank, Ilana. |
| The fate of diazotroph (N2 fixers) derived carbon (C) and nitrogen (N) and their contribution to vertical export of C and N in the Western Tropical South Pacific Ocean was studied in OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment). Our specific objective during OUTPACE was to determine whether autocatalytic programmed cell death (PCD) is an important mechanism affecting diazotroph mortality and a factor regulating the vertical flux of organic matter and thus the fate of the blooms. We sampled at three long duration (LD) stations of 5 days each (LDA, LDB, and LDC) where drifting sediment traps were deployed at 150, 325 and 500 m depths. LDA and LDB were characterized by high chlorophyll a (Chl a) concentrations (0.2–0.6 µg L−1) and dominated... |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00419/53048/53985.pdf |
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| Stenegren, Marcus; Caputo, Andrea; Berg, Carlo; Bonnet, Sophie; Foster, Rachel A.. |
| The abundance and distribution of cyanobacterial diazotrophs were quantified in two regions (Melanesian archipelago, MA and subtropical gyre, SG) of the Western Tropical South Pacific using nifH qPCR assays. UCYN-A1 and A2 host populations were quantified using 18S rRNA qPCR assays including one newly developed assay. All phylotypes were detected in the upper photic zone (0–50 m), with higher abundances in the MA region. Trichodesmium and UCYN-B dominated, composing 81–100 % of nifH copies detected. Het-1 was the next most abundant, and co-occurred with het-2 and het-3. The two UCYN-A lineages were least abundant (<1.0–1.5 % of total nifH copies) and poorly detected (> 47 %). Abundance of the UCYN-A hosts mirrored their respective symbionts; UCYN-A1... |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00420/53126/54083.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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