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Factors limiting heterotrophic bacterial production in the southern Pacific Ocean
1Laboratoire de Microbiologie, Géochimie et Ecologie Marines (LMGEM), CNRS UMR 6117, Univ. de la Méditerranée, Campus de Luminy – Case 901, 13 288 Marseille cedex 9, France
2CNRS, Laboratoire d'océanographie de Villefranche, 06 230 Villefranche-sur-Mer; Université Pierre et Marie Curie – Paris VI, Laboratoire d'océanographie de Villefranche, 06 230 Villefranche-sur-Mer, France
3Laboratoire d'Océanographie et de Biogéochimie (LOB), CNRS UMR 6535, Université de la Méditerranée, Campus de Luminy – Case 901, 13 288 Marseille cedex 9, France
4Department of Oceanography & Center for Oceanographic Research in the eastern South Pacific, University of Concepcion, Casilia 160-C, Concepcion, Chile
Abstract. The role of potential factors limiting bacterial growth was investigated along vertical and longitudinal gradients across the South Eastern Pacific Gyre. The effects of glucose, nitrate, ammonium and phosphate additions on heterotrophic bacterial production (using leucine technique) were studied in parallel in unfiltered seawater samples incubated under natural daily irradiance. Longitudinally, the enrichments realized on the subsurface showed three types of responses. From the Marquesas plateau (8° W to approx 125° W), bacteria were not bottom-up controlled, as confirmed by the huge potential of growth in non-enriched seawater (43±24 times in 24 h). Within the Gyre (125° W–95° W), nitrogen alone stimulated leucine incorporation rates by a factor of 5.6±3.6, but rapidly labile carbon (glucose) became a second limiting factor (enhancement factor 49±32 when the two elements were added). Finally from the border of the gyre to the Chilean upwelling (95° W–73° W), labile carbon was the only factor stimulating heterotrophic bacterial production. Interaction between phytoplankton and heterotrophic bacterial communities and the direct versus indirect effect of iron and macronutrients on bacterial production were also investigated in four selected sites: two sites on the vicinity of the Marquesas plateau, the centre of the gyre and the Eastern border of the gyre. Both phytoplankton and heterotrophic bacteria were limited by availability of nitrogen within the gyre, but not by iron. While iron limited phytoplankton at Marquesas plateau and at the eastern border of the gyre, heterotrophic bacteria were only limited by availability of labile DOC in those environments.
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Citation: Van Wambeke, F., Bonnet, S., Moutin, T., Raimbault, P., Alarçon, G., and Guieu, C.: Factors limiting heterotrophic bacterial production in the southern Pacific Ocean, Biogeosciences Discuss., 4, 3799-3828, 2007. Bibtex EndNote Reference Manager
