[M-IS08] 古気候・古海洋変動

[MIS08-P23] 底生有孔虫群集解析による最終退氷期における北西太平洋の溶存酸素極小層の拡大と強化

*酒井 恵祐¹、大串 健一¹、芝原 暁彦² (1.神戸大学大学院人間発達環境学研究科、2.福井県立大学恐竜学研究所)

キーワード：底生有孔虫、最終退氷期、溶存酸素極小層、北西太平洋、Bølling/Ållerød

During the last deglaciation, the oxygen minimum zone (OMZ) at 1 km water depth in the northwestern Pacific Ocean intensified. However, time-series fluctuations of the upper layer of the OMZ are poorly understood. Fossil benthic foraminifera are useful indicators of historic deoxygenation at the seafloor due to their specific patterns of adaptation to dysoxic environments. Thus, we studied benthic foraminifera assemblages in a sediment core taken from a water depth of 777 m off of Hokkaido, North Japan, to reconstruct changes in the upper layer of the OMZ during the last deglaciation. The results suggested that dysoxic species such as Brizalina seminuda and Buliminella tenuata increased rapidly during the Bølling/Ållerød warming event, implying severe oxygen depletion. Similar dysoxic assemblages were recorded at 1 km water depth in this region. We concluded that the upper limit of the OMZ in the northwestern Pacific expanded during the last deglaciation, due to an increase in biological production and decrease in intermediate water ventilation.