Oradora: Ana Brito (Centro de Oceanografia, FCUL)
Abstract: The objective of this study was to understand the bio-optical properties of phytoplankton in the Western Iberian coast, an important area of the North-East Atlantic. Although chlorophyll a satellite products have been one of the most important ocean colour products for oceanography, providing a synoptic and global view of phytoplankton abundance, they currently lack information on the community structure, which is crucial for ecological modelling and ecosystem integrated studies. In order to assess the usefulness of different existing methods to differentiate Phytoplankton Functional Types (PFT) or Phytoplankton Size Classes (PSC), phytoplankton samples were analysed for pigments and absorption spectra and three different modelling approaches were applied to the in-situ data. Water samples were collected in five different areas, four of which located near the shore and another in the open ocean, in a seamount region. The analysed approaches provided information on the pico-, nanoand microplankton fractions, either from spectral or pigment data and results differed significantly. The output obtained using modelling approaches based on the spectral properties of phytoplankton showed high specific absorption coefficients ranging from 0.02 to 0.08 m2.(mg chl a)-1 between 400 to 500 nm for microplankton. Results acquired through spectral and pigment-based approaches differed significantly. Overall, spectral data was contributing for the identification of less microplankton than existent based on the pigment analysis. This study pointed out local properties of the communities which justify the lack of fitting of the model, such as the fact that one of the most important group of microplankton, i.e. diatoms, is composed by small cells rather than large.