ENVIRONMENTAL CHANGES OF LAKES NAKAUMI AND SHINJI

Nakaumi湖和Shjii湖是日本海的沿海湖泊，通过各种回声测深方法并在分析重力岩心和海底采样样品的基础上，对整个地区进行了调查。这些资料使得用精确的古地理图描述了从200yB.P.到100yB.P.的八个湖泊发展阶段成为可能。特别是详细地分析了Hudoki(Nara)期(8世纪)以来的湖泊地史，阐明了中世纪暖期和小冰期的全球降温。这些都在古地理地图上反映得相当清楚。从海平面变化的角度收集和分析了Nakaumi湖和Shinci湖周围的考古资料，发掘了Eshima岛的历史遗址，以重建奈良时代的历史和环境，并将其与8世纪出云·奥库尼·福多基的书面历史相关联。这些都是为了说明上述古地理图。长期以来一直被指定为Nakaumi湖最大填海土地的Honjo地区，通过SideScanSonar和Atlas Deso 20和Uniom的回波测深进行了详细调查，以提供有用的数据，以便在不久的将来更好地利用这一指定地区。在不干扰表层的前提下，对中密湖表层沉积物进行了细致的采集，并用电子显微分析仪的色图方法研究了柱状沉积物中C、S和Fe的垂直元素分布。结果表明，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.