Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 4 6 2007 10.5194/bg-4-941-2007 http://www.biogeosciences.net/4/941/2007/ http://www.biogeosciences.net/4/941/2007/bg-4-941-2007.html http://www.biogeosciences.net/4/941/2007/bg-4-941-2007.pdf 941 956 2007-11-08 Growth and specific P-uptake rates of bacterial and phytoplanktonic communities in the Southeast Pacific (BIOSOPE cruise) S. Duhamel solange.duhamel@univmed.fr T. Moutin F. Van Wambeke B. Van Mooy P. Rimmelin P. Raimbault H. Claustre Aix-Marseille Université, Laboratoire d'Océanographie et de Biogéochimie, LOB-UMR 6535 CNRS, OSU/Centre d'Océanologie de Marseille, 13288 Marseille, Cedex 09, France Aix-Marseille Université, Laboratoire de Microbiologie, Géochimie et Ecologie Marines, LMGEM-UMR 6117 CNRS, OSU/Centre d'Océanologie de Marseille, 13288 Marseille, Cedex 09, France Department of Marine Chemistry and Geochemistry, Wood Hole Oceanographic Institution, MS #4, Wood Hole, MA 02543, USA CNRS, Laboratoire d'océanographie de Villefranche, 06230 Villefranche-sur-Mer, France; Université Pierre et Marie Curie-Paris 6, Laboratoire d'océanographie de Villefranche, 06230 Villefranche-sur-mer, France Predicting heterotrophic bacteria and phytoplankton specific growth rates (μ ) is of great scientific interest. Many methods have been developed in order to assess bacterial or phytoplankton μ. One widely used method is to estimate μ from data obtained on biomass or cell abundance and rates of biomass or cell production. According to Kirchman (2002), the most appropriate approach for estimating μ is simply to divide the production rate by the biomass or cell abundance estimate. Most methods using this approach to estimate μ are based on carbon (C) incorporation rates and C biomass measurements. Nevertheless it is also possible to estimate μ using phosphate (P) data. We showed that particulate phosphate (PartP) can be used to estimate biomass and that the P uptake rate to PartP ratio can be employed to assess μ. Contrary to other methods using C, this estimator does not need conversion factors and provides an evaluation of μ for both autotrophic and heterotrophic organisms. We report values of P-based μ in three size fractions (0.2–0.6; 0.6–2 and >2 μm) along a Southeast Pacific transect, over a wide range of P-replete trophic status. 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