Inouchi, Yoshio

Kuwae, Michinobu

Yoshikawa, Shusaku

井内, 美朗

加, 三千宣

吉川, 周作

Records of East Asian summer monsoon changes has been revealed widely from China and Tibetan Plateau. In Japanese Islands, however, there is less record of summer precipitation. Therefore, relationship between the East Asian summer monsoon changes in China and the summer precipitation changes in Japanese Islands is still unclear. Here, we examine diatom valve flux in lacustrine sediment of Lake Biwa for the past 140ka using the 140-m core, and to test it possibility as a proxy for summer precipitation. Furthermore, we discuss the relationship between the East Asian summer monsoon changes in China and the summer precipitation changes in Japan. Comparison of diatom concentration records with records of paleoprecipitation indices, such as pollen, C/N ratio, and lignin from Lake Biwa sediments indicates that higher diatom concentrations represent wetter climatic conditions, and that lower concentrations represent drier climatic conditions. Meanwhile, comparison of recent monitoring data for diatom production with meteorological data shows that there is a good relationship between annual diatom production and values of annual summer precipitation during periods of May to October. Thus, records of diatom concentrations (also those of diatom valve flux) are of great utility as a proxy for inferring paleoprecipitation levels. Based on the diatom valve flux, summer precipitation levels in Lake Biwa watershed region are high during 132-115,102-101,31-29,7-0kacalBP, and low during 113-103,60-55,12kacalBP. These trends of the record show similar pattern to that of record of the East Asian summer monsoon intensity inferred from magnetic susceptibility from Chinese Loess Plateau. The result suggests that summer precipitation change in Japan is closely associated with the change in the East Asian summer monsoon intensity. However, there are several problems of age estimates for the Takashima-oki core. Each four ^C dates at levels of 10-15m shows approximately 30kacalBP, therefore, sedimentation rates in this level are much higher than those at the other levels. The sedimentation rates do not match either the above mentioned conclusion that is based on ages of published tephrochronologies for the age/depth model, or those from other core closely drilled to the Takashima-oki core. Thus, this conclusion has remained suspensive.第14回名古屋大学タンデトロン加速器質量分析計シンポジウム(平成13 (2001)年度)報

琵琶湖湖底コア, 年間珪藻殻堆積量から見た過去14万年間の日本の夏季降水量変動と東アジアモンスーン

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