Natural succession of microalgal communities during the cold-water season and the impact of increased solar irradiance on sea ice algae

• Main Author: Enberg, Sara
• Other Authors: Gradinger, Rolf, University of Helsinki, Faculty of Biological and Environmental Sciences, Department of Environmental Sciences, Helsingin yliopisto, bio- ja ympäristötieteellinen tiedekunta, ympäristötieteiden laitos, Helsingfors universitet, bio- och miljövetenskapliga fakulteten, miljövetenskapliga institutionen
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Helsingin yliopisto 2017
• Subjects: ice algae; Sea ice
• Online Access: http://hdl.handle.net/10138/224574

The winter season in polar and sub-polar areas is commonly described as a dormant phase for microalgae, especially in the water column, although the sea ice is a habitat for diverse and active communities. However, these areas are subject to changing environmental conditions due to global warming and changes in ultraviolet radiation. This thesis describes the natural succession of microalgal communities in the water column and sea ice during the cold-water winter season. Results show that the cold-water season is dynamic with various microalgal communities and their variable photosynthetic activity in the water column and sea ice. Although microalgal biomass is relatively low throughout the cold-water season, especially in the water column, natural succession during the cold-water season can be divided into five different groups based on microalgal community composition. Similar to the water column, algal succession in the sea ice begins with low biomass and domination of various flagellates. Thereafter the biomass in the ice increases and the community shifts to being diatom and dinoflagellate dominated. In late spring, sea ice algae communities differ between the ice layers from the top to the bottom ice, and the highest biomass in the bottom ice layer (dominated by colonial pennate diatoms). However, the contribution of released dominant sea ice algae to the water column community is not significant, and the spring bloom community is largely formed by pelagic species of the early open-water season. This thesis also describes the effect of enhanced solar irradiance on the microalgal community at various ice depths.We studied the effects of enhanced solar irradiance (including PAR and UVR) on the microalgal community at various depths of the spring ice during a three-week experimental in situ study. Results show that the largest effect of enhanced solar irradiance occurs in the top 10-cm layer of ice, but even beneath this layer the diminishing amount of irradiance and change in light quality increase the ...