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Biochemical characteristics and bacterial community structure of the sea surface microlayer in the South Pacific Ocean
1Université Pierre et Marie Curie-Paris6, UMR7621; F66650 Banyuls-sur-Mer, France ; CNRS, UMR7621, F-66650 Banyuls-sur-Mer, France
2CNRS, Laboratoire d'Océanographie de Villefranche, 06230 Villefranche sur Mer, France; Université Pierre et Marie Curie-Paris6, Laboratoire d'Océanographie de Villefranche, 06230 Villefranche sur Mer, France
3Université de la Rochelle, Pôle Science, CRELA, UMR6217, Av. Michel Crépeau, 17042 La Rochelle cedex 01, France
4Laboratoire de Microbiologie, Géologie et Ecologie Marine (LMGEM), CNRS 6117, Université de la Méditerranée, Campus de Luminy – Case 901, 13288 Marseille cedex 9, France
Abstract. The chemical and biological characteristics of the surface microlayer were determined during a transect across the South Pacific Ocean in October-December 2004. Concentrations of particulate organic carbon (1.3 to 7.6-fold) and nitrogen (1.4 to 7), and POC:PON ratios were consistently higher in the surface microlayer as compared to subsurface waters (5 m). The large variability in particulate organic matter enrichment was negatively correlated to wind speed. No enhanced concentrations of dissolved organic carbon were detectable in the surface microlayer as compared to 5 m, but chromophoric dissolved organic matter was markedly enriched (by 2 to 4-fold) at all sites. Based on pigment analysis and cell counts, no consistent enrichment of any of the major components of the autotrophic and heterotrophic microbial community was detectable. CE-SSCP fingerprints and CARD FISH revealed that the bacterial communities present in the surface microlayer had close similarity (>76%) to those in subsurface waters. By contrast, bacterial heterotrophic production (3H-leucine incorporation) was consistently lower in the surface microlayer than in subsurface waters. By applying CARD-FISH and microautoradiography, we observed that Bacteroidetes and Gammaproteobacteria dominated leucine uptake in the surface microlayer, while in subsurface waters Bacteroidetes and Alphaproteobacteria were the major groups accounting for leucine incorporation. Our results demonstrate that the microbial community in the surface microlayer closely resembles that of the surface waters of the open ocean. However, even short time periods in the surface microlayer result in differences in bacterial groups accounting for leucine incorporation, probably as a response to the differences in the physical and chemical nature of the two layers.
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Citation: Obernosterer, I., Catala, P., Lami, R., Caparros, J., Ras, J., Bricaud, A., Dupuy, C., van Wambeke, F., and Lebaron, P.: Biochemical characteristics and bacterial community structure of the sea surface microlayer in the South Pacific Ocean, Biogeosciences Discuss., 4, 2809-2844, 2007. Bibtex EndNote Reference Manager
