Abstract: As a part of the Arctic Ocean ecosystem, the sea ice community plays important roles in primary production and the carbon cycle. In this study, we used the fluorescence microscopy technique to analyze samples of the pack ice community, collected from the central Arctic Ocean in summer 2012. The results showed that the average integrated biomass was （105.85±53.41） mg C•m⁻², of which heterotrophic bacteria comprised 47.2%, followed by diatoms (26.7%), heterotrophic flagellates (18.2%), autotrophic flagellates (6.9%), and ciliates (1.0%). An autotrophic flagellate bloom was observed at the bottom of the high-latitude station (87°39.598′N, 123°43.454′E). The community of this station was in the late period of diatom algal bloom and there was considerable melting of the upper sea ice layer, which could have led to a suitable habitat at the bottom for autotrophic flagellate growth (the higher ratios of N/P). It is suggested that the melting of sea ice in recent years has had obvious influence on the pack ice community in the Arctic Ocean. For example, the biomass of the heterotrophic taxa has increased and heterotrophic bacteria have replaced diatoms as the dominant group.

Key words: central area of Arctic Ocean, pack ice, ice biota, melting ice, environmental correlation