Photosynthetic and pigment responses of sea-ice microalgae to changes in light intensity and quality

Photoadaptation of sea-ice microalgae in springtime: photosynthesis and carboxylating enzymes

“…The investigations of Cota (1985) in the High Arctic and of Palmisano et al (1985) in the Antarctic have suggested that ice algae are markedly shade-adapted. On the other hand, Gosselin et al (1985), Rochet et al (1986) and Barlow et al (1988) found that ice algae in Hudson Bay were not an obligate shade flora, and that they adapted to the seasonally increasing irradiance. In Hudson Bay, Gosselin et al (1985) have reported a critical value of 7.6 ~[ E i n m-'s-' below which there was no population ' Contribution to the programs of GIROQ (Groupe interuniversitaire de recherches oceanographiques du Quebec) and of the Maunce-Lamontagne Institute (Department of Fisheries and Oceans)…”

Lack of agreement among models for estimating the photosynthetic parameters

“…Potential sources of experimental errors include incubation and filtration procedures, measurements of low irradiances (Richardson 199 l), sampling and temporal alias of the sampling (Platt et al 1984), differences in the spectral quality of experimental and natural irradiance, and algal response to the spectral distribution of light (Rochet et al 1986;Sathyendranath et al 1989). Larger analytical variability associated with a!…”

Chlorophyll and photosynthetic efficiency of size-fractionated sea-ice microalgae (Hudson Bay, Canadian Arctic)

“…was lower than that of large diatoms, which are known to b e well adapted to the very low light intensities of the ice environment (e.g. Gosselin et al 1985, Rochet et al 1986. During most of the sampling season, the under-ice photon fluence rate was below 50 pEinst m P 2 S-' (Barlow et al in press).…”

“…Combining the fractions could also reduce the effects of possible inaccuracies resulting from sequential filtering. Rochet et al (1986) found that I, of ice algae incubated under blue-green light was >40 liEinst m-* S-' during the whole sampling season, which indicates that maximum photon fluence rate in the incubator (43 ~~E i n s t m-2 S-') was not high enough to achieve saturation. Consequently, the initial slope (photosynthetic efficiency; cuB) was the only parameter estimated for the photosynthesis versus irradiance curves.…”

“…On 3 different occasions, 6 subsamples (125 m1 on 29 Apr; 60 m1 on 3 and 7 May) were inoculated with 10 pCi H14C03 and put in a Hawaiian-type incubator (Doty & Oguri 1959), in which under-ice water was continuously circulated in order to keep the temperature close to natural conditions. Incubations were under 43, 17, 11, 8, 1 and 0 pEinst m-' S-' of blue-green light that approximated the colour of the under-ice illumination (Rochet et al 1986); bags of black tulle were used to obtain the various light intensities, and the dark bottles were wrapped in aluminum foil. After 4 h incubations, samples were sequentially filtered onto 5.0, 1.0 and 0.8 pm Nuclepore filters.…”