Deep-sea benthic foraminiferal record of the paleoceanography in the southern Okinawa Trough over the last 20 000 years

摘要

Quantitative analyses have been carried out on benthic foraminifera from 66 samples of Core 255 in the southern Okinawa Trough, in combination with the stable isotopic analyses of planktonic and benthic foraminifera and AMS ~(14)C dating, in order to reconstruct the history of change under deep water conditions and surface paleoproductivity over the last 20 000 years. The variations in the ratio of agglutinants in benthic foraminiferal fauna and the ratio of fragments in planktonic foraminiferal fauna indicate higher carbonate dissolution during the postglacial stage than during the glacial stage. The distribution of species and the results of Q-mode factor analysis show that there are three distinctly different benthic foraminiferal assemblages during the glacial, deglacial and postglacial stages in the Okinawa Trough over the last 20000 years: the glacial Bulimina aculeata assemblage (especially the dominant species Uvigerina peregrina) is associated with high surface primary productivity and organic matter content in sediments; the postglacial Uvigerina asperula assemblage corresponds to low surface primary productivity; while the deglacial Chilostomella oolina assemblage possibly reflects low oxygen content in bottom water.