High-time-resolution reconstruction of sedimentary environment of Lake Biwa during the past ten and several thousand years by inorganic chemical determination.

我们用中子活化分析和电感耦合等离子体发射光谱分析的方法，分别采集了琵琶湖250m厚的表层沉积物(间隔1.4-2m)、3个长约10m的活塞芯(间隔6 cm)、末次冰期/全新世过渡期间距绥格斯湖中心2 cm的不同岩心，以及表层沉积物和琵琶湖和绥格苏湖周围陆地的样品进行了对比。本研究的目的有三个：(1)评价As含量作为古水深的地球化学指标；(2)寻找与冰川/间冰期气候变化和快速气候变化同步的地球化学指标；(3)研究地球化学变化与岩心周围构造运动的关系。研究结果表明：(1)砷含量不能准确反映古水深。或者，锂铬矿的数量是有希望的。(2)琵琶湖表层Th/Sc比值的时间序列与气候变化同步，并与风尘通量相关。而在末次冰期/全新世过渡时期，我们无法从约10m的毒芯中探测到Th/Sc比值的变化。我们发现了绥格苏湖中心的大降水时代。(3)成功地探测到湖泊周围构造运动的化学变化。

We performed both neutron activation analysis and ICP-AES of sediments taken from the 250 m thick top bed of Lake Biwa at 1.4-2 m intervals, three ca.10 meter long piston cores at 6cm intervals, varved core from the center of Lake Suigetsu at 2 cm intervals during the last glacial/Holocene transition, and the samples from surface sediments and from land around Lake Biwa and Lake Suigetsu for the comparison. The goals in this study are three : (1) Evaluation of As contents as the geochemical proxy of paleo-water-depth ; (2) Quest of geochemical proxy for synchronisation with glacial/-interglacial climatic changes and rapid climatic change ; (3) Research of the relationship between the geochemical change and tectonic movements around the cores. The research results are as follows : (1) Arsenic content is invalid for the accurate proxy of paleo-water-depth. Alternatively, the amount of lepidochrosite is hopeful. (2) The time series of Th/Sc ratios in top bed of Lake Biwa is synchronized with climatic changes and also correlated with the reported aeolian dust flux. While, we cannot detect the change of Th/Sc ratios at the last glacial/Holocene transition from the ca.10m poison cores. We found the times of great precipitation from the core of Lake Suigetsu. (3) We can detect the chemical variation as the result of tectonic movement around Lakes successfully.