Diatom records from lacustrine sediments of Lake Biwa during the past 400 000 years

In 1986, Takashima-oki core boring was carried out in the central part of Lake Biwa. The sediment samlpes are composed mainly of silty clay sediments extending over the past c400 000 yr. The sediments are intercalated with many volcanic ash layers, and thus are rich in time control. We analysed for diatom with high-resolution on the sediments, and have obtained the following results. 1) The variations of the total number of diatom valves in 2g dry sample, which is interpreted as the fluctutions of diatom productivity, have occurerd widely off the main basin of Lake Biwa. 2) The profile of the total number of diatom valves during the past 400 000 yr shows good correlation with the marine oxygen isotope profile. The fluctuation of the total number of diatom valves in Lake Biwa reflects global climate changes sensitively. That is to say, the total number of diatom valves increases under warm and wet paleoclimatic conditions, and decreases under cold and dry conditions. Stages 1 through 9 of the marine oxygen isotope stratigraphy can be recognized. Moreover, for the short-time fluctuations of the total number of diatom valves, correlation can be made with the detailed marine oxygen isotope stratigraphy. The Biwako diatom horizons (BDH) with rare diatom valves are well correlated with the cold-climate events of the marine oxygen isotope stratigraphy. The BDHs at 8.5m, 19.0m, 28.0m, 35.3m, 43.3m, 53.6m, 63.5m, 80.2m, 86.9m and 93.5m in depth correspond to stages 2.2, 4, 5.2 (5b), 5.4 (5d), 6.2, 6.4, 6.6, 7.4, 8.2 and 8.4 respectively.