ENVIRONMENTAL CHANGES OF LAKES NAKAUMI AND SHINJI

Nakaumi湖和Shinji湖是日本海沿岸的海洋湖泊，已通过各种回声探测方法并在分析重力岩心和海底取样获得的样本的基础上对整个地区进行了调查。这些资料使我们能够用精确的古地理图来阐明从2万年前到100万年前湖泊发育的8个阶段，特别是详细地分析了自世纪Hudoki（奈良）期以来湖泊的地史，阐明了中世纪的中世纪暖期和小冰期的全球变冷。这些在古地理图上反映得很清楚。从海平面变化的角度收集和分析了中海湖和新寺湖周围的考古资料，并挖掘了江岛的历史遗址，以重建奈良时代的历史和环境，并将其与世纪的泉之国不动木的书面历史相关联。这些都是用来说明上述古地理图的。本庄地区长期以来一直被指定为中海湖最大的填海土地，通过侧扫声纳和Atlas Deso 20和Uniboom的回声测深进行了详细调查，为不久的将来更好地利用该指定地区提供了有用的数据。在不扰动表层的情况下，对中海湖表层沉积物进行了细致的采集，并利用电子探针微量分析仪（Electron Prove Microanalysis）的彩色填图法，研究了沉积物中C、S和Fe元素的垂直分布。土壤中总氮和硫酸盐浓度随深度的增加而降低。

Lakes Nakaumi and Shinji are maritime coastal lakes a long the Sea of Japan, and have been surveyed the entire areas by various methods of echo-sounding and on the basis of analysing samples obtained by gravity cores and bottom sampling. These data have made it possible to illustrate with precise paleogeographic maps eight stages of lake development from 20,000 y.B.P to 100 y.B.P. Especially the geohistory of the lakes since the Hudoki (Nara) Period (8th Century) was analysed in detail in the present study, which have clarified the Medieval Warm Period in the Middle Age and the global cooling during the Little Ice Age. These are reflected quite sharply in the paleogeographic maps. Archeological data around Lakes Nakaumi and Shinji have been collected and analysed from the viewpoint of sea-level changes and the historic site at Eshima Island was excavated to reconstruct the history and environment of Nara Age and to correlate these to the written history of Izumonokuni Fudoki in 8th Century. These were referred to illustrate the above paleogeographic maps. The Honjo Area, which has long been appointed as a largest reclamed land in Lake Nakaumi, was surveyed in detail by echo-soundings of Sidescan Sonar and Atlas Deso 20 and Uniboom to provide useful data for the better utility of this appointed area in near future. Surface sediments of Lake Nakaumi were collected carefully without disturbing the top layer and vertical elementary distributions of C,S and Fe within the core sediments were investigated by a color mapping method of Electron Prove Microanalyser. It as been clarified that the concentration of total nitrogen and sulfate decrease with depth.