Diatom Records from Lacustrine Sediments of Lake Biwa during the Past 400,000 Years.

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  • 琵琶湖湖底堆積物，過去４０万年間の珪藻化石記録
  • ビワコ コテイ タイセキブツ カコ 40マンネンカン ノ ケイソウ カセキ キ

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Abstract

In 1986, Takashima-oki core boring was carried out in the central part of Lake Biwa. The sediment samples are composed mainly of silty clay sediments extending over the past ca. 400, 000 years. The sediments are intercalated with many volcanic ash layers, and thus are rich in time control. We analyzed for diatom with high-resolution on the sediments, and have obtained the following results, <br>1. The variations of the total number of diatom valves in 1g dry sample, which is interpreted as the fluctuations of diatom productivity, have occurred widely off the main basin of Lake Biwa.<br>2. The profile of the total number of diatom valves during the past 400, 000 years 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.<br>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 coldclimate 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, 86.9 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.

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