Foraminiferal assemblage distribution was used to reconstruct the palaeoenvironmental conditions that prevailed during the deposition of the core MD179-3312 in the eastern margin of the Japan Sea. One hundred six benthic foraminifera species belonging to 50 genera and seven planktonic foraminifera species belonging to three genera were identified in this core. Cluster analyses of both benthic and planktonic foraminifera data led to the identification of seven biofacies which demonstrate the palaeoceanographic history of the Japan Sea since 130 cal kyr BP. Species diversity, evenness and dominance were measured to understand effects of environmental changes on benthic foraminifera distribution. The results indicate that changes in organic matter and oxygen content throughout the core clearly influence community structure of benthic foraminiferal assemblages and species diversity. The light colored non-laminated layers found in particular at the lowermost and uppermost core areas indicate both high diversity and equitability, corresponding to high vertical mixing and good ventilation of subsurface water which would produce suitable living environments for most species; conversely, the dark colored thinly laminated layers (TL layers), in particular TL-1 and TL-2, indicate both low diversity and equitability, corresponding to dysoxic conditions caused by a severe decrease in bottom water oxygenation which would produce unsuitable living environments for most species, with only a few species adapted to this depleted oxygen condition able to survive.
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Vol. 19 • No. 2