島根・鳥取県中海における堆積速度と堆積環境

概要

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In order to study sedimentation environments and sedimentation rates of Lake Nakaumi, Shimane and Tottori Prefectures, the Pb-210 and Cs-137 radioactivities were measured in 14 cores taken on the September in 1996. The sedimentation rate varied in the range of 0.1-1.9 cm/y. Those of the western and southern areas are larger, because some rivers run into the lake at there. Detrital materials are transported through the Ohhashi river, the Iu (Ou) river and the Iinashi river and deposit near the estuaries. Such a high sedimentation rate is supported by the chemical components such as U and K (Pb-214 and K-40) in the sediments, because they suggest the provenance. The fluxes and inventories of radionuclides that indicate the rate and the amount of accumulation correlated with the sedimentation rates. The inventories of excess Pb-210 and Cs-137 are in good correlation with each other (R=0.87). However the ratios of excess Pb-210 inventory to Cs-137 inventory for the cores of Lake Nakaumi are about 11, between those for the Sea of Japan (about 38) and Lake Shinji (about 5). The sources of radionuclides are supposed to be terrestrial fallout, suspended particles carried from rivers and seawater. Although the terrestrial fallout may be the major source, it is considered that the others are more important in contrast to the case of Lake Shinji.
日本地球化学会の論文
2002-12-20