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Nutrients limitation of primary productivity in the Southeast Pacific (BIOSOPE cruise)
1University of Southern California, Wrigley Institute for Environmental Studies, 3616 Trousdale Parkway – AHF 108, Los Angeles, CA 90089-0371, USA
2Laboratoire d'Océanographie de Villefranche, UMR 7093, CNRS and Université Pierre et Marie Curie, BP 08 06238 Villefranche sur mer Cedex, France
3Dalhousie University, Department of Oceanography, 1355 Oxford Street, Halifax, NS, B3H 4J1, Canada
4Institute of Microbiology ASCR, Opatovický mlýn, 37981 Tøeboò and University of South Bohemia, Zámek, 37333 Nové Hrady, Czech Republic
5Centre d'Océanologie de Marseille, Campus de Luminy, 13288 Marseille Cedex 09, France
6Rutgers University, Institute of Marine and Costal Sciences, 71 Dudley road, New Brunswick, NJ 08901-8521, USA
7University of California at Santa Cruz, Ocean Sciences Department, Earth and Marine Sciences Building, Santa Cruz, California 95064, USA
8Station Biologique de Roscoff, UMR 7144, CNRS and Université 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 nitrogen 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) measured across the whole gyre (3 stations situated in the center, the western and the eastern edge), photosynthesis and 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 nitrogen fixation in our experiments, even after iron and/or phosphate additions, and cyanobacterial nifH 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.
Discussion Paper (PDF, 1408 KB) Interactive Discussion (Closed, 4 Comments) Final Revised Paper (BG)
Citation: Bonnet, S., Guieu, C., Bruyant, F., Prášil, O., Van Wambeke, F., Raimbault, P., Grob, C., Moutin, T., Gorbunov, M. Y., Zehr, J. P., Masquelier, S. M., Garczarek, L., and Claustre, H.: Nutrients limitation of primary productivity in the Southeast Pacific (BIOSOPE cruise), Biogeosciences Discuss., 4, 2733-2759, 2007. Bibtex EndNote Reference Manager
