| Summary: | The maximum quantum yield of charge separation in photosystem II (ФPSIImax) was assessed for studying the physiological state of different ice algal communities. By using Rapid Light Curves, relative electron transfer rates (rETR) and photosynthetic parameters were calculated to determine whether photo-acclimation and light saturation (Ek) was evident for the algae sampled during early spring to early summer (March-June). The highest photosynthetic responses, ФPSIImax were found in thin ice and ridge communities in addition to the water column where a Phaeocystis pouchetii bloom took place in early June. The study also indicates that in order to provide reliable estimates for the photosynthetic parameters (αrETR, rETRmax and Ek), the samples need to reach light saturation plateau rETRmax, i.e. be exposed to high enough irradiances, in order to understand the algae sample's ecological and physiological context. Challenges like low biomass of ice algae early in the sampling period provided rETR versus E curves that did not reach rETRmax. Modelling non-linear curves for these led to over-estimation of the saturation light parameter Ek.
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