地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
日本海-黄土地帯-地中海トランセクトにおける過去240万年間の大気循環変動
チベット/ヒマラヤの上昇史との関係
福澤 仁之大井 圭一山田 和芳岩田 修二鳥居 雅之
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1997 年 106 巻 2 号 p. 240-248

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Recent atmospheric circulations over the Asian Continent have been influenced by the Himalayan Range and the Tibetan Plateau as a wind barrier. Based on recent meteorological data, the existence of the Himalaya-Tibet within the troposphere has caused meandering of the Westerlies, intense activity of the Asian Monsoon and appearance of the Easterlies. Meandering of the Westerlies has led to increase precipitation in the East Asia region including northeastern China and Japan, and has formed the soils with poorly crystalized illite minerals in the Chinese Loess Plateau and the Japanese Islands. In nothern India and Nepal including the frontal basin of the Himalayan Range such as the Kathmandu Basin, intense activity of the Asian Monsoon has led abruptly to increase precipitation named “onset of monsoon”. Also, appearance of the Easterlies from the Himalaya-Tibet to northern Africa within the upper part of the troposphere has led to dry and spread the arid area in the northern Africa.
There are many sedimentary records indicating Late Quaternary climatic changes around the Himalayan-Tibetan Plateau. We expected to determine the formation age of recent atmospheric circulation. This age indicates when the Himalayan-Tibetan Plateau was abruptly uplifted and elevated. In other words, formation ages of more humid climate in northeastern China, the Japanese Islands and the Kathmandu Basin, and the driest climate in the northern Africa are useful to determine age of uplift and elevation of the Himalayan-Tibetan Plateau.
On the base of above-mentioned evidences and hypothesis, we attempted to investigate magnetic susceptibility of the loess-paleosol sequence in the Luochuan area of th e northeastern China, and illite crystallinity of loess-paleosol sequence in the Kathmandu Basi n and deep-sea sediments of the Japan Sea and the Mediterrannean Sea. Because characteristic changes of magnetic susceptibility and illite crystallinity indicate dry -wet oscillations as useful detectors.
As results, we clarified three evidences as follows:
1) Large amplitudes of magnetic susceptibility oscillations by large pricipitation in interglacial periods appeared in the Luochuan loess -paleosol sequence during last 600ka.
2) Large amplitudes of illite crystallinity oscillations by large precipitations caused decomposition of illite minerals appeared in the deep-sea sediments of the Sea of Japan during the last 800ka and in the loess-paleosol sequence of the Kathmandu Basi n during the last 1.1Ma. 3) Amplitudes of illite crystallinity oscillation during the last 800k a were smaller than those amplitudes since 800ka ago.
Investigation mentioned above indicates that critical uplift and elevations of the Himalayan-Tibetan Plateau achieved to induce activity of westerlies, easterlies and the Asian Monsoon, and suggests that determined ages of critical elevation caused atmospheric circulation changes range from 0.6 million years to 1.1 million years ago.

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