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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bgd-11-17151-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
https://doi.org/10.5194/bgd-11-17151-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Submitted as: research article 10 Dec 2014

Submitted as: research article | 10 Dec 2014

Review status
This discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The revised manuscript was not accepted.

Nitrogen fixation in the Southern Ocean: a case of study of the Fe-fertilized Kerguelen region (KEOPS II cruise)

M. L. González1, V. Molina2, L. Florez-Leiva3, L. Oriol4, A. J. Cavagna5, F. Dehairs5, L. Farias6, and C. Fernandez4,7,8 M. L. González et al.
  • 1Graduate Program in Oceanography, Department of Oceanography, University of Concepcion, Concepción, Chile
  • 2Faculty of Natural Science, University of Playa Ancha, Valparaíso, Chile
  • 3Biology Program, University of Magdalena, Santa Marta, and Oceanography Program, University of Antioquia, Medellin, Colombia
  • 4Sorbonne Universités, UPMC Univ Paris 06, UMR 7621, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, 66650 Banyuls/mer, France
  • 5Analytical, Environmental and Geo-Chemistry, Earth System Sciences research group, Vrije Universiteit Brussel, Belgium
  • 6Laboratory of Oceanographic and Climate Processes (PROFC), Department of Oceanography, University of Concepción, and Center for Climate Change and Resilience Research (CR2), Concepción, Chile
  • 7CNRS, UMR 7621, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, 66650 Banyuls/mer, France
  • 8Department of Oceanography, COPAS SurAustral program and Interdisciplinary center for Aquaculture Research (INCAR), University of Concepción, Chile

Abstract. N2 fixation rates were measured during the KEOPS2 cruise in the HNLC area of Southern Ocean and in naturally iron-fertilized waters (Kerguelen Island 49.25° S, 69.58° E) using the 15N isotopic technique. We detected N2 fixation within the mixed layer at all stations, from the surface to 140 m depth. The data shows high variability with rates ranging between 0.42 and 20.11 nmol N L−1 d−1. The highest rates were concentrated in the euphotic layer and maximum values were obtained north of polar front (station F-L), which coincide with a positive N* ([NO3]–16[PO4]), high chlorophyll concentration and dissolved iron. N2 fixation rates were also obtained in stations with moderate (A3-2; E-4W) and also low (R-2) iron levels as well as Chl a, suggesting that beside the microbial biomass, its composition/structure is a driving factor controlling N2 fixation activities. Molecular analysis showed a diazotrophic community dominated by heterotrophic bacterioplankton. Size fractioned experiments indicated that most of N2 fixating activities came from <5 μm community and it was on line with molecular analysis revealing a low diversity diazotrophic community dominated by heterotrophic bacterioplankton. This study shows for first time N2 fixation is occurring in the Southern Ocean, at rates exceeding previous reports for high latitudes. Our findings suggest an indirect role of dFe in the regulation of N2 fixation through the enhancement of regenerated primary production and the availability of phytoplankton-derived dissolved organic matter, which in turn may stimulate heterotrophic bacterioplankton.

M. L. González et al.
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Interactive discussion
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Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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M. L. González et al.
M. L. González et al.
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This study shows for first time N2 fixation is occurring in the HNLC area of Southern Ocean and in naturally iron-fertilized waters, at rates exceeding previous reports for high latitudes (up to 20.11 nmol N L-1 d-1). Diazotrophs were identified as heterotrophic bacterioplankton; with an indirect role of dFe in the regulation of this process. Fertilization enhancing regenerated primary production may control N2 fixation via the availability od DOM for heterotrophic bacterioplankton.
This study shows for first time N2 fixation is occurring in the HNLC area of Southern Ocean and...
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