Responses of the lower tropic level marine ecosystems to environmental variability in the Arctic Ocean.

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I conducted this study based on the observational data taken during the research cruises by R/V Mirai for the Japan-Canada Joint Arctic Study (JWACS) in autumn of FY2002 and 2004. The purpose of this study is to understand influences of physical and chemical environmental variation on the structure of the lower trophic level ecosystems in the western Arctic Ocean. I particularly focus on the spatial variation of ecology of the two copepod species, Calanus hyperboreus and C.glacialis, which dominated secondary producers in this region. The major finding of the results of FY2002 cruise was region-specific lower-trophic level structure and production We defined the four regions with the respective physical-biological characteristics. Coastal Pacific water inflow and dynamics of seasonal sea ice retreat were considered as the possible causes of the observed regional variations of the lower trophic level. As for the results of the FY2004 cruises, I also found the spatial variation in developmental timing of copepods between the east and west of Chukuchi Plateau (160-l70゜W) : more advanced stage of the copepods with high diatom availability was observed in the west while slow copepod development and poor phytoplankton abundance were observed in the east. Timing of ice edge retreat did not explain this results, but east-west contrast of surface layer stratification, which was presented by the complex water mess structure of this region, was considered as the direct determinant of the spatial difference in the ecosystem structure. Reduction of the Arctic sea iice for these decades has been reported, and these results implicated the future sea ice reduction and associated changes in the surface layer structure could drastically alter the ecosystem structure and biological production in the western Arctic Ocean.