[M-IS18] 古気候・古海洋変動

[MIS18-P08] A geoarchaeological approach for estimating last glacial temperatures using coupled isotopic analyses of fossil snails and stalagmites from limestone caves in Okinawa, Japan

*浅海 竜司¹、本堂 陸斗²、植村 立³、藤田 祐樹⁴、山崎 真治⁵、Shen Chuan-Chou^6,7、Wu Chung-Che^6,8、Jiang Xiuyang⁹、高柳 栄子¹、新城 竜一^10,11、狩野 彰宏¹²、井龍 康文¹ (1.東北大学大学院理学研究科、2.東北大学理学部、3.名古屋大学大学院環境学研究科、4.国立科学博物館、5.沖縄県立博物館・美術館、6.Department of Geosciences, National Taiwan University、7.Research Center for Future Earth, National Taiwan University、8.Department of Chemistry and Applied Biosciences, ETH Zurich、9.College of Geography Science, Fujian Normal University、10.総合地球環境学研究所、11.琉球大学理学部、12.東京大学大学院理学系研究科)

キーワード：遺跡洞窟、石筍、包有水、淡水棲巻貝、酸素同位体組成、最終氷期温度

We applied a new geoarchaeological method with two carbonate archives, which are fossil snails from Sakitari Cave and stalagmites from Gyokusen Cave, on Okinawa Island, Japan, to reconstruct surface air temperature variations over the northwestern Pacific Ocean since the last glacial period. Oxygen isotope ratios of modern and fossil freshwater snail shells were determined to infer annual and seasonal air temperature variations. The observational and analytical data confirm that oxygen isotopic values of fluid inclusion waters in the stalagmite can be regarded as those of spring waters at the sites where snails lived. Our results indicate that the annual mean, summer, and winter air temperatures were lower by 6–7 °C at ca. 23 thousand years ago (ka) and 4–5 °C at ca. 16–13 ka than those of the present day. Our reconstruction implies that surface air cooling was possibly two times greater than that of seawater around the Ryukyu Islands during the Last Glacial Maximum, which potentially enhanced the development of the East Asian summer monsoon during the last deglaciation. Considering the potential uncertainties in the temperature estimations, the climatic interpretations of this study are not necessarily definitive due to the limited number of samples. Nevertheless, our new geoarchaeological approach using coupled isotopic determinations of fossil snails and stalagmite fluid inclusion waters can be useful for reconstructing snapshots of seasonally resolved time series of air temperatures during the Quaternary.