MEASURING PHOTOSYNTHETIC ACTION SPECTRA OF NATURAL PHYTOPLANKTON POPULATIONS¹

Abstract

ABSTRACT The photosynthetic response, defined as the initial slope of the photosynthesis‐irradiance curve, was determined spectrally (every 25 nm from 400 to 675 nm; 25 nm half‐maximum bandpass) for natural phytoplankton populations from High Arctic, Grand Banks and Sargasso Sea waters, as well as for populations living in the lower margin of sea ice off Newfoundland, All spectra were similar in shape with a maximum at 425–450 nm, a broad shoulder to 550 nm, a valley from 600 to 650 nm and a rise at 675 nm. The error resulting from the use of spectrally averaged initial slope to predict photosynthesis under different optical and fluid dynamical conditions at sea is discussed.