Summary
HPLC-pigment measurements, Production vs Irradiance and daily primary production experiments were carried out on the Kerguelen Plateau during the KEOPS cruise in January and February 2005. The respective contribution of three phytoplankton size classes, namely micro- (> twenty micron), nano- (between two and twenty micron) and picophytoplancton (< two micron), to the total algal biomass, was determined by using a biomarker pigment approach. Results showed that the whole sampling area was dominated by microphytoplankton, with almost exclusively large diatoms in the iron-enriched bloom region of the Kerguelen Plateau. The contribution of nanophytoplankton ranges between twenty and sixty percent at stations located outside the plateau, while the picophytoplankton contribution always remains very low (no more than ten percent). Combined to class-specific photophysiological parameters obtained on a global dataset, these contributions are introduced in a bio-optical primary production model to assess primary productivity rates specific to the three phytoplankton groups. Results are compared to in situ measurements both within and away from the iron-enriched region. Discrepancies between the global and in situ-adjusted parameterizations are examined and discussed.