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Importance of N2-fixation on the productivity at the north-western Azores current/front system, and the abundance of diazotrophic unicellular cyanobacteria
Riou, V.; Fonseca-Batista, D.; Roukaerts, A.; Biegala, I.; Prakya, S.; Loureiro, C.; Santos, M.; Muniz-Piniella, A.; Schmiing, M.; Elskens, M.; Brion, N.; Martins, M.; Dehairs, F. (2016). Importance of N2-fixation on the productivity at the north-western Azores current/front system, and the abundance of diazotrophic unicellular cyanobacteria. PLoS One 11(3): e0150827. https://dx.doi.org/10.1371/journal.pone.0150827

Additional data:
In: PLoS One. Public Library of Science: San Francisco. ISSN 1932-6203; e-ISSN 1932-6203
Peer reviewed article  
Available in  Authors 
    Vlaams Instituut voor de Zee: Open access 292105 [ download pdf ]
Keyword
    Marine/Coastal
Authors  Top 
  • Riou, V.
  • Fonseca-Batista, D.
  • Roukaerts, A.
  • Biegala, I.
  • Prakya, S.
  • Loureiro, C.
  • Santos, M.
  • Muniz-Piniella, A.
  • Schmiing, M.
  • Elskens, M.
  • Brion, N.
  • Martins, M.
  • Dehairs, F.
Abstract
    To understand the impact of the northwestern Azores Current Front (NW-AzC/AzF) system on HCO3--and N2-fixation activities and unicellular diazotrophic cyanobacteria (UCYN) distribution, we combined geochemical and biological approaches from the oligotrophic surface to upper mesopelagic waters. N2-fixation was observed to sustain 45–85% of the HCO3--fixation in the picoplanktonic fraction performing 47% of the total C-fixation at the deep chlorophyll maximum north and south of the AzF. N2-fixation rates as high as 10.9 µmol N m-3 d-1 and surface nitrate d15N as low as 2.7‰ were found in the warm (18–24°C), most saline (36.5–37.0) and least productive waters south of the AzF, where UCYN were the least abundant. However, picoplanktonic UCYN abundances up to 55 cells mL-1 were found at 45–200m depths in the coolest nutrient-rich waters north of the AzF. In this area, N2-fixation rates up to 4.5 µmol N m-3 d-1 were detected, associated with depth-integrated H13CO3--fixation rates at least 50% higher than observed south of the AzF. The numerous eddies generated at the NW-AzC/AzF seem to enhance exchanges of plankton between water masses, as well as vertical and horizontal diapycnal diffusion of nutrients, whose increase probably enhances the growth of diazotrophs and the productivity of C-fixers.
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