PHOTOADAPTATION OF SEA-ICE MICROALGAE IN THE BARENTS SEA

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-degrees-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 alpha-B (photosynthetic efficiency) were generally low, e.g. 0.0025-0.0078 mg C (mg CHLa)-1 h-1 (mu-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, alpha-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.