Primary and bacterial production in sea ice in the northern Baltic Sea

The temporal variation of ice primary and bacterial production along with i ce algal, bacterial and heterotrophic flagellate biomass were studied at a coastal station in the northern Baltic Sea throughout the ice-covered perio d of 1996 (January to April). Ice core samples were taken every week and an alyzed for abundance and production of different microorganisms. In additio n, physical and chemical parameters were measured. The ice algae were limit ed by light during the first 3 mo of the study. The algal production showed a peak in the middle of April, which coincided with a marked increase in l ight availability. Shortly after that, the system became phosphorus deplete d and primary production decreased rapidly. Bacterial biomass and productio n rates were relatively low and stable before the ice algal bloom. After th e ice algal bloom, bacterial production increased rapidly, while the biomas s remained low. The growth rate of small heterotrophic flagellates (<10 mu m), calculated from increase in biomass, was more than 1 order of magnitude higher than the bacterial production rate following the ice algal bloom. T hus, small heterotrophic flagellates were using food sources other than bac teria for growth after the ice algal bloom. On an annual basis, the ice alg al and bacterial production accounted for <1% and <0.1% respectively of the total production (ice + pelagic) due to a short ice-covered season. During the ice-covered season, however, the ice algae accounted for 10 % of the t otal algal production, while ice bacterial production was 0.2 % of the tota l bacterial production.