Photosynthetic parameters of the entire euphotic phytoplankton of the Bransfield Strait, Summer 1985

Abstract

The photosynthetic parameters αB, PBm, and Ik were derived from the relationship between primary productivity (P) and irradiance (I) for mixed samples, each mixture consisting of seven samples of phytoplankton collected from different depths, between the surface and 35 m at eight different sampling stations in the Bransfield Strait in January–February 1985. The αB values obtained in this study were considerably higher than those generally reported for phytoplankton from a single depth in polar waters. These higher values may be attributed to the fact that most of the phytoplankton in the mixed samples came from depths with limiting irradiances, which had a greater yield than surface phytoplankton. The PBm value we obtained was lower than that reported by other authors, possibly because the mixed sample phytoplankton have saturation points at low light intensity. Our IK values confirmed the ability of phytoplankton in these latitudes to reach maximum photosynthesis rates with low densities of photonic flux. When treated as independent parameters, the αB and PmBvalues showed a significant correlation for each sampling station. The efficiency of the entire euphotic phytoplankton of the water column, estimated as ∫0euPdz/∫0euBdz or Integral Assimilation Number (IAN), showed a predictable significant correlation with the αB values calculated from the entire euphotic phytoplankton. Areas with high surface biomass were as productive as those with low surface phytoplankton biomass. Areas with low surface phytoplankton biomass showed higher αB values than areas with high surface biomass, which suggests, that, the αB values for the entire photosynthesizing phytoplankton in the water column may have greater predictive value than the αB values for the phytoplankton from a single depth. This finding should be taken into account when satellites are used for studying marine production processes, especially in areas with very different euphotic depths and surface phytoplankton concentrations.