Abstract The history of the East Asian monsoon and the relationship between the development of the monsoon climate, tectonics and global climate are complicated and controversial. Earlier studies have indicated that the East Asian monsoon fluctuated in the Asian interior during the Pliocene. Thus, the chemical weathering record in coastal regions of East Asia can be the key to elucidating its evolution as well as the Kuroshio Current variability. The present study clarifies the chemical weathering conditions in southwest Japan based on the concentrations of major elements and rare earth elements (REEs) in lacustrine muddy sediments. The chemical weathering was moderate between 4.4 and 3.8 Ma. Between 3.8 and 3.4 Ma, chemical weathering significantly intensified, as indicated by the high values of the chemical index of alteration that reached a maximum of 98, as well as the high concentrations of REEs and light REEs against heavy REEs and kaolinite-rich clay mineral compositions, despite the wide variation in source rock compositions and grain sizes. The degree of chemical weathering remained moderate during the early Pleistocene. The intense chemical weathering on land in southwest Japan from 3.8 to 3.4 Ma may have been regulated by alternating periods of warm and humid climate brought by the invasion of the Kuroshio Current and the intensification of the East Asian summer monsoon.

中文翻译：

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日本西南部上新世沉积物的主要元素和稀土元素组成：对古风化和古气候的影响

摘要 东亚季风的历史和季风气候的发展、构造和全球气候之间的关系是复杂而有争议的。较早的研究表明，东亚季风在上新世期间在亚洲内陆波动。因此，东亚沿海地区的化学风化记录可能是阐明其演化以及黑潮变化的关键。本研究根据湖相泥质沉积物中主要元素和稀土元素 (REE) 的浓度，阐明了日本西南部的化学风化条件。化学风化在 4.4 到 3.8 Ma 之间中等。在 3.8 到 3.4 Ma 之间，化学风化显着加剧，尽管烃源岩成分和富含高岭石的粘土矿物成分变化很大，但蚀变的化学指数值高达 98，并且相对于重稀土和富含高岭石的粘土矿物成分而言，稀土和轻稀土的浓度很高。颗粒大小。在早更新世期间，化学风化程度保持中等。日本西南部陆地从 3.8 到 3.4 Ma 的强烈化学风化可能受到黑潮入侵和东亚夏季风增强带来的暖湿气候交替时期的调节。在早更新世期间，化学风化程度保持中等。日本西南部陆地从 3.8 到 3.4 Ma 的强烈化学风化可能受到黑潮入侵和东亚夏季风增强带来的暖湿气候交替时期的调节。在早更新世期间，化学风化程度保持中等。日本西南部陆地从 3.8 到 3.4 Ma 的强烈化学风化可能受到黑潮入侵和东亚夏季风增强带来的暖湿气候交替时期的调节。