Sea ice algae are important marine primary producers that may contribute as much as 15% of total global carbon fixation. The difficulties of studying photosynthesis in ice have, however, hampered accurate assessments of their productivity, and much previous research has involved liquid-phase measurements on thawed ice, which is artificial and unlikely to be representative of conditions experienced by ice algae in situ. We report here the first ever application of Imaging-PAM fluorometry as a method to estimate algal biomass and photosynthetic parameters in intact sea ice. We collected sea ice cores from the Kangerlussuaq Fjord, Greenland, over two weeks in March 2011, and used Imaging-PAM to explore the spatial distribution of algal biomass (predominantly pennate diatoms), fluorescence yield, and light response curves. Algae were largely confined to the lowest 1 cm of the ice column, where temperatures were high enough to allow extensive brine channel development in the ice. The Imaging-PAM allowed clear visualisation of their highly patchy spatial distribution in channels between laminar ice crystals. The ice grew at a rate of ca. 8 mm/day during the first half of the study, and the diatoms were able to migrate with ice growth. Furthermore, increases in maximum fluorescence (Fm) and photosynthesis yield (Y) allowed us to document the progression of a spring bloom in algal biomass and activity. Maximum light intensities in the ice algal communities were ca. 40 µmol PPFD m-2 s-1 and light response curves revealed shade-adapted photobiology at all times. We conclude that Imaging PAM fluorometry offers new insights into the distribution and development of algae in sea ice, and is a promising tool particularly for assessing spatial patchiness, seasonal changes, and geographical variation in sea ice primary production.
Main Research Area:
CO2 assimilation in plants:From Genome to Biome, 2011