Photoadaptation of sea-ice microalgae in the Barents Sea

Summary Variations in under-ice scalar irradiance, P vs I parameters and the CHLa C^–1 ratio of natural assemblages of sea-ice microalgae from the Barents Sea growing at -1.8°C in May and September 1988 are described, including one diurnal station. CHLa C^–1 ratios of 0.031–0.071 mg mg^–1 indicate shade adaptated assemblages both in May and September. Values for ^B (photosynthetic efficiency) were generally low, e.g. 0.0025–0.0078 mg C (mg CHLa)^–1 h^–1 (mol m^–2 s^–1)^–1, and should be typical for self-shaded algae in mats or aggregates of about 4 mm thickness. Provided no self shading and the typical spectral distribution of light under ice without algae, ^B would, however, be about 2.5 times higher. Photoinhibition of the photosynthetic response was negligible. Maximum carbon uptake P _m ^B was 0.15–0.24 and 0.032–0.088 mg C (mg CHLa)^–1 h^–1 in May and September, respectively. Diurnal variations were small, particularly for P _m ^B . Calculations of the maximum specific gross growth rate yielded an upper limit of 0.20–0.24 and 0.01–0.04 d^–1 for assemblages in May and September, respectively; the latter may have been in a resting stage.Contribution No. 245, Trondhjem Biological Station