[M-IS34] 古気候・古海洋変動

[MIS34-02] 過去5万年間の琵琶湖の湖底堆積物の編年：放射性炭素年代・火山灰層序・環境磁気学的指標の統合

*林田 明¹、北川 浩之²、竹村 恵二³ (1.同志社大学理工学部環境システム学科、2.名古屋大学環境学研究科、3.京都大学理学研究科地球熱学研究施設)

キーワード：琵琶湖, 年代モデル, 最終氷期

The Quaternary sedimentary sequence of Lake Biwa, located in central Japan, provides continuous terrestrial records of past climate changes in East Asia including detailed records of Asian monsoon activity from the Middle Pleistocene to the Holocene. We constructed a common chronological framework for multiple sediment cores from Lake Biwa for the past 50 kyrs. An age- depth model of a 18.42-m long piston-core (BIW07-6), recovered between Takashima and Okinoshima Island in central part, was constructed under the age constraints of thirteen AMS radiocarbon dates of terrestrial macrofossil and six known-ages of widespread tephra layers. Using this age model, we estimated the model ages of ten horizons at which characteristic features were observed in the time series of anhysteretic remanent magnetization (ARM). ARM is a measure of fine ferrimagnetic mineral flux into the sediment, representing a proxy of hydrological changes around Lake Biwa. Therefore the characteristic features of the ARM variation serve as tie-points of core-to-core correlations in Lake Biwa, as well as the horizons of tephra deposits. We thus obtained age-depth curves for other core samples, which were well constrained with the tephra ages, the ARM events and additional radiocarbon dates from each core. The integrated age model has an acceptable accuracy to assess terrestrial environmental changes in millennial scales and can be adapted for paleolimnological studies in other regions.