Articles | Volume 5, issue 1
Biogeosciences, 5, 215–225, 2008

Special issue: Biogeochemistry and Optics South Pacific Experiment...

Biogeosciences, 5, 215–225, 2008

  20 Feb 2008

20 Feb 2008

Nutrient limitation of primary productivity in the Southeast Pacific (BIOSOPE cruise)

S. Bonnet1, C. Guieu1, F. Bruyant2, O. Prášil3, F. Van Wambeke4, P. Raimbault4, T. Moutin4, C. Grob1, M. Y. Gorbunov5, J. P. Zehr6, S. M. Masquelier7, L. Garczarek7, and H. Claustre1 S. Bonnet et al.
  • 1Laboratoire d'Océanographie de Villefranche, UMR 7093, CNRS and Université Pierre et Marie Curie, BP 08 06238 Villefranche sur mer Cedex, France
  • 2Dalhousie University–Department of Oceanography, 1355 Oxford Street Halifax, NS, B3H 4J1, Canada
  • 3Institute of Microbiology ASCR, Opatovický mlýn, 37981 Trebon and University of South Bohemia, Zámek, 37333 Nové Hrady, Czech Republic
  • 4Centre d'Océanologie de Marseille - Campus de Luminy, 13288 Marseille Cedex 09, France
  • 5Rutgers University, Institute of marine and Costal Sciences, 71 Dudley road, New Brunswick, N. J. 08901-8521, USA
  • 6University of California Santa Cruz, Ocean Sciences Department, 1156 high street, Santa Cruz, CA 95064, USA
  • 7Station Biologique de Roscoff, UMR 7144, CNRS and Univ. Pierre et Marie Curie, BP 74, 29682 Roscoff Cedex, France

Abstract. Iron is an essential nutrient involved in a variety of biological processes in the ocean, including photosynthesis, respiration and dinitrogen fixation. Atmospheric deposition of aerosols is recognized as the main source of iron for the surface ocean. In high nutrient, low chlorophyll areas, it is now clearly established that iron limits phytoplankton productivity but its biogeochemical role in low nutrient, low chlorophyll environments has been poorly studied. We investigated this question in the unexplored southeast Pacific, arguably the most oligotrophic area of the global ocean. Situated far from any continental aerosol source, the atmospheric iron flux to this province is amongst the lowest of the world ocean. Here we report that, despite low dissolved iron concentrations (~0.1 nmol l−1) across the whole gyre (3 stations located in the center and at the western and the eastern edges), primary productivity are only limited by iron availability at the border of the gyre, but not in the center. The seasonal stability of the gyre has apparently allowed for the development of populations acclimated to these extreme oligotrophic conditions. Moreover, despite clear evidence of nitrogen limitation in the central gyre, we were unable to measure dinitrogen fixation in our experiments, even after iron and/or phosphate additions, and cyanobacterial nif H gene abundances were extremely low compared to the North Pacific Gyre. The South Pacific gyre is therefore unique with respect to the physiological status of its phytoplankton populations.

Final-revised paper