Photosynthetic parameters of arctic marine phytoplankton: Vertical variations and time scales of adaptation

Abstract

In the eastern Canadian arctic the photosynthesis‐irradiance curves of phytoplankton from the 50% and 1% light levels differ mainly in their susceptibility to photoinhibition. The photoinhibition parameters of deep populations and the intensity of the deep chlorophyll maximum were correlated with N 2 , the bulk stratification parameter of the water column. Comparison of data from the same region in different periods suggests that the characteristic susceptibility to photoinhibition requires 2–6 weeks to develop once a population is isolated below a pycnocline. Insensitivity to photoinhibition developed much more quickly when a population from the chlorophyll maximum was exposed to surface light. The threshold of photoinhibition increased rapidly, reaching surface intensities within 4–6 h. The adaptation is sufficiently rapid that phytoplankton from the chlorophyll maximum should be stressed only briefly when transported to the surface by a mixed‐layer‐deepening event.