Light response and acclimation of macroalgae in a changing Arctic

This thesis investigates ice-associated and under-ice algal communities, and the controlling role of light in the Arctic pack ice region. Changes in the light regime are a consequence of the substantial environmental changes happening in the Arctic. To this end the research vessel Lance was frozen into the pack ice north of Svalbard (80.2–82.8°N) for nearly half a year from January to June 2015 during the Norwegian young sea ICE (N-ICE2015) expedition to study the new, thinner sea ice regime and associated environmental and ecosystem processes. The presented results from the spring and early summer season (April–June) suggest that an under-ice phytoplankton bloom can develop and grow under the opaque ice cover because open and refrozen leads acted as light conduits into the water column. The ratio of photoprotective (PPC) to photosynthetic (PSC) carotenoids indicated that the bloom was low-light acclimated, which supports the conclusion of in situ growth under the ice pack. The pigment ratios were in addition related to the slope of in situ absorption measurements between 488 and 532 nm (affected by absorption by PPC and PSC, respectively) to evaluate a method to assess the photoacclimation state of phytoplankton blooms in situ. We also studied the young ice in a refrozen lead which had a thin ice and snow cover and high light transmittance of up to 0.41. Under-ice irradiance, Ed(PAR) (photosynthetically active radiation, 400 to 700 nm) was up to 350 μmol photons m-2 s-1, and the high light conditions resulted in accumulation of cellular photoprotective pigments (mycosporine-like amino acids (MAAs) and PPC). Biomass in the lead ice (mg Chl a m-2) did not exceed the surrounding older and thicker ice with low light availability (Ed(PAR)