Photosynthetic and respiratory characteristics of an Arctic ice algal community living in low light and low temperature conditions

The massive development of the ice algal community commonly observed under first-year sea ice was studied with particular attention to photosynthetic and respiratory characteristics of ice algae at low temperature and low light conditions. Field experiments were carried out in April and May 1992 at Resolute Passage in the Canadian Arctic. Under ca. 200 cm of sea ice with a snow cover of less than 7 cm, ice algal biomass increased from 3.7 to 88.7 Chlam−2 with growth rates increasing from 0.17 to 0.23 doublings d−1, although the development was disturbed between 1 and 6 May. The photosynthetically active radiation (PAR) measured at the bottom of the sea ice near midday was between 8.6 and 1.5 μmol photons m−2 s−1 (1.0 and 0.1% of the surface irradiance), and the water temperature was near −1.8°C. In response to these low irradiance levels, ice algae exhibited a high α (the initial slope of the photosynthesis vs. irradiance relationship) of 0.26 μg C μg Chla−1 h−1 (μ mol photons m−2 s−1)−1. The dark respiration contributed up to 35% of the gross photosynthetic rare and was estimated to be 0.22 μg C μg Chla−1 h−1 on average. Considering the value of α and the dark respiration rate, light compensation was estimated to be 0.8 μmol photons m−2 s−1 for the ice algal community, which was enough for ice algae to maintain the positive photosynthesis at the bottom of the sea ice at the maximum daily irradiance. Using a numerical model with these estimated parameters, we evaluated the net positive diel photosynthesis under natural environmental conditions. The numerical model also suggested that the long day length in the late spring and summer in the Arctic region allowed the algae to maintain positive net photosynthesis even after the massive development of the ice algal community.