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Ecology and biogeochemistry of contrasting trophic environments in the South East Pacific by carbon isotope ratios on lipid biomarkers
1International Atomic Energy Agency – Marine Environment Laboratories, 4, quai Antoine 1er, MC 98000, Monaco
2Laboratoire d'Océanographie et de Biogéochimie (UMR 6535 CNRS), Centre d'Océanologie de Marseille, Univ. de la Méditerranée, Campus de Luminy, 13288 Marseille Cx 09, France
3BDSI, Université de Perpignan, 52 avenue Paul Alduy, 66860 Perpignan, France
4Laboratoire d'Océanographie de Villefranche, Observatoire Océanologique, INSU/CNRS/UPMC, UMR 7093, BP 08, 06230 Villefranche-sur-Mer, France
Abstract. The distribution of lipid biomarkers and their carbon isotope composition was investigated on suspended particles from different contrasting trophic environments at six sites in the South East Pacific. High algal biomass with diatom-related lipids was characteristic in the upwelling zone, whereas haptophyte lipids were proportionally most abundant in the nutrient-poor settings of the centre of the South Pacific Gyre and on its easter edge. Dinoflagellate–sterols were minor contributors in all of the studied area and cyanobacteria-hydrocarbons were at maximum in the high nutrient low chlorophyll regime of the subequatorial waters at near the Marquesas archipelago.
The taxonomic and spatial variability of the relationships between carbon photosynthetic fractionation and environmental conditions for four specific algal taxa (diatoms, haptophytes, dinoflagellates and cyanobacteria) was also investigated. The carbon isotope fractionation factor (εp) of the diatom marker varied over a range of 16‰ along the different trophic systems. In contrast, εp of dinoflagellate, cyanobacteria and alkenone markers varied only by 7–10‰. The low fractionation factors and small variations between the different phytoplankton markers measured in the upwelling area likely reveals uniformly high specific growth rates within the four phytoplankton taxa, and/or that transport of inorganic carbon into phytoplankton cells may not only occur by diffusion but by other carbon concentrating mechanisms (CCM). In contrast, in the oligotrophic zone, i.e. gyre and eastgyre, relatively high εp values, especially for the diatom marker, indicate diffusive CO2 uptake by the eukaryotic phytoplankton. At these nutrient-poor sites, the lowest εp values for haptophytes, dinoflagellates and cyanobacteria infer higher growth rates compared to diatoms.
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Citation: Tolosa, I., Miquel, J.-C., Gasser, B., Raimbault, P., Azouzi, L., and Claustre, H.: Ecology and biogeochemistry of contrasting trophic environments in the South East Pacific by carbon isotope ratios on lipid biomarkers, Biogeosciences Discuss., 4, 4653-4696, 2007. Bibtex EndNote Reference Manager
