TAKAOKA Sadao Assistant Professor, Faculty of Science Tokyo Metropolitan University, 理学部, 助手 (90260786)
IWATA Shuji Professor, Faculty of Science Tokyo Metropolitan University, 理学部, 教授 (60117695)
北川 浩之 国際日本文化研究センター, 助手 (00234245)
|Budget Amount *help
¥2,300,000 (Direct Cost : ¥2,300,000)
Fiscal Year 1996 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1995 : ¥1,600,000 (Direct Cost : ¥1,600,000)
Mineralogical characteristics of last 2000 year records in meromictic lake, Lake Suigetsu, are the indicators of eolian dust concentrations, sea-level and rainfall changes in central Japan. Non-glacial varved sediment in Lake Suigetsu shows that there was no large influx of terrestrial materials into lake basin Sequential chages of illite crystallinity and quartz / illite ratio in late Quaternary fine-grained sediments at Site 794 and Site 795 of ODP Leg 127 of were well correlated to standard records of oxygen isotope change by Prell et al. (1986). This suggests that these parameters are useful to detect eolian dust concentration within sediments. In other words, occurrence of hydrated illite and small concentration of illite suggest that paleosol were greatly formed under wet climate in northern China. Sea-level and rainfall changes were detected by iron mineral composition and chlorite / illite ratio.
Investigations show that climatic changes in northern China were parallel to sea-le
vel changes of the Wakasa Bay in southern part of the Japan Sea. In 250,820,1170,1320,1500 and 1880 A.D., sea-level was risen in the Wakasa Bay when northern China was in wet climate. It is because that Asian monsoon was active in globally warm climate at these times, and that active monsoon took humid atmosphere into northern China. In 250,820,1050-1200,1320,1500 and 1880 A.D., there seems to have been heavy rainfall around Lake Suigetsu with sea-level rising in the Wakasa Bay. This suggests of influxing of Tsushima Current, supplying humid atmosphere and rising of sea-level. In 350-550 and 1350-1400 A.D., preciptations were heavy in the Wakasa region, though there are no rising of sea-level, and dry and cool climate in China.
On the basis of mentioned above, there are sea-level rising around the Tsushima Strait and intense influx of the Tsushima Currents into the Sea of Japan before the beginning of warm climate in China and coastal area along the Sea of Japan. This fact sggests that sea-level rising in Tsushima Strait may be a trigger to accelerate intensity of monsoon activity in the East Asia. Less