60 ky high resolution record of the environmental change from Sediments of Lake Biwa, Japan

Lake Biwa is the largest freshwater lake in Japan, measuring 22.6 km wide by 68 km long and having a maximum depth of 104 m. In 2007, we carried out seismic survey and piston coring operation in northern part of Lake Biwa. We implemented with 10-KHz acoustic sonar equipment with maximum resolution of 6 cm and maximum acoustic penetration depth of 20 m. We cruised the 18 transverse lines which intervals are about 1.85 km. These reflecting data differed according to location, and showed 10 geologic layers. Most of them will be correlated with tephra layers. We recovered piston cores at six localities having different sedimentation rates. Analyses of the core samples are ongoing in various disciplines. We present initial results from lithological description, measurements of magnetic susceptibility and tephrostratigraphic correlation of the core sediments with the seismic data. After the constructing the age-depth model of core sediments, we discover successive sedimentary change due to the depth, and spatial and temporary distribution of sedimentary supply change related with lake level change and climatic change during about 60ka.