Toward a taxon-specific parameterization of bio-optical models of primary production: A case study in the North Atlantic

[1] As part of the Programme Ocean Multidisciplinaire Meso Echelle (POMME) in the North Atlantic, an extensive data set of high-pressure liquid chromatography pigment concentrations, phytoplankton absorption coefficients, primary production measurements, and P versus E curves has been acquired. This data set is analyzed with the objective of testing whether photosynthetic performances of natural phytoplankton communities are related to taxonomic characteristics. This objective is addressed in two ways. The first approach concerns the bulk photosynthetic performances of the water column: the water column photosynthetic cross section, ψ*, equals 0.088 m2 gChla−1, i.e., ∼25% higher than the average for the world ocean. Using multiple regression, size-specific values of ψ* are subsequently derived: carbon storage by water column is more efficient with microphytoplankton (ψ* = 0.135 m2 gChla−1) than with nanophytoplankton (0.089 m2 gChla−1) or picophytoplankton (0.064 m2 gChla−1). The second (independent) approach examines the correlations between photophysiological properties and several abiotic and biotic variables. The correlations are weak, if any, between photophysiological properties and abiotic factors (temperature, nitrate concentration, and irradiance), while significant correlations are reported with biotic factors (proportion of the different phytoplankton groups, average size of the phytoplankton assemblage). Our results suggest that when large phytoplankton populations predominate at the expense of smaller ones, the specific absorption coefficient is expectedly lower, while other photophysiological properties αB, PmaxB, and Φcmax, are higher. The agreement between both independent approaches points out that large phytoplankton (essentially diatoms) are potentially more efficient in carbon storage than any other phytoplankton groups on a chlorophyll a or light absorption basis.