Temporal change of fossil datom assemblages in the surface sediment cores from the northern lake biwa, Japan

Lake Biwa is the largest and longest-lived lake of fresh water in Japan. Its environment changes have been recorded in the bottom sediments. To elucidate relationship between fossil diatom assemblages and climate conditions in Lake Biwa, we performed diatom analysis for the surface sediments, associated with water content, total organic carbon, total nitrogen, Cs-137, and Pb-210 measurements. Temporal changes of fossil diatom assemblage were revealed in intervals of 1 to 3 years for the past 50 years, and 4 diatom zones were recognized on the basis of CONISS cluster analysis. Zone 1 (before AD 1973) is characterized by dominant Stephanodiscus suzukii associated with Aulacoseira nipponica and lack of Fragilaria crotonensis. Zone 2 (AD 1973-1986) is dominated by Aulacoseira nipponica with S. suzukii.. Zone 3 (AD 1986-1996) is characterized by predominance of S. suzukii and Zone 4 (AD 1986-2012) is shown by increase of Fragilaria crotonensis. Increasing of F. crotonensis seems to relate with warm temperature higher than 14?. Abundance of Aul. nipponica has positive relation to low winter temperature and high winter precipitation. S. suzukii seems to be favorable for intermediate temperature. These relationships suggest that temporal change of fossil diatom assemblage might be controlled by climate changes in the lateQuaternary.