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Volume 7, issue 7
Biogeosciences, 7, 2227–2244, 2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 7, 2227–2244, 2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.

  20 Jul 2010

20 Jul 2010

Ultraphytoplankton basin-scale distribution in the eastern Mediterranean Sea in winter: link to hydrodynamism and nutrients

M. Denis1, M. Thyssen1, V. Martin1, B. Manca2, and F. Vidussi3,* M. Denis et al.
  • 1Laboratoire de Microbiologie, Géochimie et Ecologie Marines, Université de la Méditerranée, CNRS UMR 6117, 163 avenue de Luminy, Case 901, 13288 Marseille cedex 9, France
  • 2Istituto Nazionale di Oceanografia e Geofisica Sperimentale – OGS, Borgo Grotta Gigante, 42/c, 34010 Sgonico (Trieste), Italy
  • 3Laboratoire d'Océanographie de Villefranche, CNRS UMR 7093, Université de Paris VI, quai de la Darse, B.P. 28, 06234 Villefranche-sur-mer cedex, France
  • *present address: Ecosystèmes lagunaires, CNRS, UMR 5119, Université Montpellier II, CP 093, Place Bataillon, 34095 Montpellier cedex 5, France

Abstract. The basin-scale distribution of ultraphytoplankton (<10 μm) was determined in the upper 200 m of the eastern Mediterranean Sea during the winter season. Four clusters were resolved by flow cytometry on the basis of their optical properties and identified as Synechococcus, Prochlorococcus, pico- (<3 μm) and nanoeukaryotes (3–10 μm). Synechococcus was the most abundant population (maximum abundance of about 37 000 cells cm−3) and contributed up to 67.7% to the overall ultraphytoplanktonic carbon biomass, whereas the contribution of Prochlorococcus never exceeded 6.5%. The maximum integrated carbon biomass was 1763, 453, 58 and 571 mg C m−2 for nanoeukaryotes, picoeukaryotes, Prochlorococcus and Synechococcus respectively. Water mass properties were analyzed on the basis of temperature and salinity distributions in order to account for the general circulation and locate the main hydrodynamic structures (fronts, gyres, transition between western and eastern basins). The effect of the main hydrodynamic structures and nutrients on the ultraphytoplankton distribution was investigated. No positive correlation between nutrients and phytoplankton could be established when considering large scales. However, below 50 m depth, nutrient ratios between particular stations were correlated to corresponding density ratios. In contrast, significant relationships were found between Synechococcus abundance and density, resulting from the impact of a gyre in southern Adriatic basin and a thermohaline front in the Ionian basin. A significant relationship was also found between picoeukaryotes and salinity in the comparison of western and eastern Mediterranean Sea.

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