Changes of dust flux and paleo-environments during the Last Glacial Age in Japanese Islands.

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1. Eolian dust flux increased during the last Glacial age more than that of the Holocene. The increases of dust flux in both stages 2 and 4 during the last Glacial age suggests an enforcement of prevailing wind and monsoon during two stages. A bigger dust flux in the stage 2 than stage 4 reflects (1) stronger westerlies and winter monsoon, and (2) a wider emergence of continental shelf which becomes an important dust source.2. Electron spin resonance (ESR) spectra of fine quartz grains less than 20 micro-meter have been measured to identify the source areas of eolian dust. Fifty-nine samples of loess, soils, paleosols and bore cores from China, Korea and Japan were measured. ESR signal intensity of eolian dust quartz is a useful tracer for the provenance of the quartz.3. The measurement values (in arbitrary unit) of eolian dust fine quartz of stage 2 in China and Korea were as follows ; Taklamakan and Quidam : 6.2 to 8.2, Upper Malan loess : 5.8 to 8.3, Korean soils : 6.0 to 7.7. The quartz of Chinese loess and Korean soils are remarkably similar to ranges of ESR intense signal. This similarity is attributed to their common eolian origin from the arid and semi-arid Asian continental areas during the isotope stage 2.4. Japanese Islands are divided into three areas from the view point of ESR spectra of fine quartz. (1) Yonaguni Island soil quartz was 9.8 originated in the Precambrian rock area of southern Asian continent. (2) Soil quartz from Okinawa to Fukui were 5.8 to 8.5 which coinsided with those of Chinese loess. It shows that eolian dust was brought from the Asian arid and semi-arid areas such as Tibetan Plateau. Taklamakan and Gobi deserts etc (3) Soil quartz from Aomori to Hokkaido were more than 10, originated in the Precambrian rock area of north Asian continent.Fine quartz of three areas were brought from the Asian continent by the prevailing winds of several ways in the stage 2.