Primary production, light absorption and quantum yields of phytoplankton from the Bellingshausen and Amundsen Seas (Antarctica)

Chlorophyll concentration, light intensity, primary production, light absorption and quantum yield were measured between 12 January 1994 and 27 March 1994 in the Bellingshausen and Amundsen Seas. Primary production and quantum yield within Bellingshausen and Amundsen Seas were typical of the high-nutrient, low-chlorophyll area of the Southern Ocean while small variations were found as a result of local conditions. Chlorophyll a (chl a) concentrations were generally low (<1 μg l^-1) in the water column, while in cases of blooms it reached 7-8 μg l^-1. The light intensity at which photosynthesis approaches saturation varied between 59 and 105 μmol q m^-2 s^-1 The initial slope of the photosynthesis curve varied between 0.02 and 0.07 μg C (μg chl a)^-1 h^-1 (μmol q m^-2 s^-1)^-1. The maximal photosynthetic rate at light saturation ranged between 1.6 and 5.4 μg C (μg chl a)^-1 h^-1. Light limitation was found within the mixing depth, while no photoinhibition was observed when surface light was 500 μmol q m^-2 s^-1. The mean spectral absorption coefficients of phytoplankton ranged between 0.018 and 0.042 m² (mg chl a)^-1 depending on the phytoplankton taxonomy. The quantum yield of photosynthesis varied between 0.027 and 0.076 mol C mol q^-1. These high quantum yields are explained by the prevailing high nutrient concentrations in this area. Light intensity plays a major role as limiting factor, even in very shallow water. The phytoplankton close to the surface did not show photoinhibition but had higher UV absorption capabilities.