Phytoplankton community structure during the record Arctic ice-melting of summer 2007

In the summer of 2007, the Arctic Ocean experienced the largest loss of ice cover yet observed. We examined the phytoplankton community composition at several stations in the NE Arctic Sector during the ATOS-Arctic cruise in July 2007, specifically in the Fram Strait and along the permanent ice edge up to 81°N. The prymnesiophyte Phaeocystis pouchetti, present exclusively in its colonial form, dominated the whole phytoplankton community, representing 82.1 ± 3.1% (mean ± SE) of the phytoplankton biovolume in the region. Diatoms, small flagellates and dinoflagellates, expected to dominate the ice-melt waters in this sector of the Arctic Ocean, were practically insignificant, representing 7.3 ± 2.4%, 6.8 ± 1.4% and 4.4 ± 1.2% of phytoplankton biovolume, respectively. The fraction of the phytoplankton biomass that comprised diatoms increased with increasing water temperature and salinity, and was, therefore, negatively associated with the increased load of ice-melt waters. In contrast, the fraction of the biomass that comprised P. pouchetii was not as clearly related to temperature and had a weak tendency to decrease with increasing temperature. This pattern was likely the result of different populations stress, as the percentage of living cells of P. pouchetii increased with increasing salinity and temperature. The exceptional dominance of the colonial form of P. pouchetii during the massive ice losses of summer 2007 provides indication of major changes in phytoplankton community structure and carbon flow with climate change in the Arctic Ocean.