Physical, Chemical And Biological Characteristics Of Pack Ice In The Arctic Ocean During Summer Seasons

A drastic ice decline in the Arctic Ocean, triggered by global warming, couldgenerate rapid changes in ice itself and upper ocean layers. The ice retreat isparticularly intense over the Canadian Basin where large ice free areas were observedsince2007. Summer pack ice biotic community of the Canada basin, Western Arctic(WA) and Central Arctic Ocean was characterized during The CHINARE2008and2010Expedition (August–September2008,2010). Bacteria, ice algae (diatoms andautotrophic flagellates) and protozoa (mainly heterotrophic flagellates) wereobserved throughout the whole ice column and underlying waters. The verticaldistribution of biotic taxa varied among sites. The integrated biomass ranged from12.3and56.7mg m-2, with an average of34.5mg m-2. Heterotrophic flagellates andbacteria were the dominant of the assemblages in pack ice, accounted for89％of theintegrated, and ice algae, which usually dominate the ice biotic community in thebottom ice layer, constituted only11％of the total. Although diatoms dominated theice-associated algal biomass, flagellates at times revealed similarly high biomass andtypically dominated in the surface layer. The low integrated biomass in the CanadianBasin, during the summer of exceptional ice retreat (2008), suggested that quick icemelting may be the key factor compared to in-situ data in more ice covered year(1994). The low salinity and nutrients throughout the whole ice column andunderlying water cumbered the formation of ice algae bloom in summer, finallyresulting in the dominance of microbial food web with bacteria and heterotrophicflagellates as the most obvious characteristics. Considering the high ratio of pack iceprimary production to the total found in previous studies, the quick change of packice community structure in summer would influence the marine ecosystem of thehigh Arctic Ocean．For the CHINARE2010Expedition, sea ice observations cover a total of tenstations within the drifting pack ice, visited during the period of ice melt from July toSeptember. The chlorophyll a concentration ranged from0.06to1.18mg m-2, with an average of0.53mg m-2. The ice algae biomass was mainly distributed in bottomlayer. There was significantly difference of algae community in bottom ice layer andunderlying water. Diatoms dominated in the community, and the maximum biomasswas34.97μg C L-1. Flagellates were the dominated taxa in the sea waters. However,whether a part of the autochthonous ice algae or entrained from the water column,flagellates add significantly to ice-associated biomass. The heterotrophs dominated inthe summer pack ice biota community. Among this, bacteria biomass varied between3.52and60.96μg C L-1.Comparing results observed between2010and2008, the algae biomassexceeded that obtained at2008by a factor of2during summer season. The diatomscontributed more significantly to algae biomass, because low sio4-cumbered theaccumulation of diatoms in sea ice during summer2008. Flagellates were shown tosignificantly contribute to ice-associated algal biomass, especially in the upper icelayer. The heterotrophs dominated in the summer pack ice biota community, whichmay be contributed to the accumulation of non-living organic carbon in the pack ice.