High-resolution reconstruction of the paleoceanographic changes in the Japan Sea in response to the rapid changes in Asian monsoon

本研究旨在利用日本海多岩心高时间分辨率重建末次冰期至全新世的日本海古海洋学变化，并与同一沉积物沉积物代用物估算的古季风强度变化进行对比，阐明日本海表层和深水环境对东亚季风格局和强度变化的响应。作为地表水环境指标，我们利用浮游有孔虫氧同位素比值、烯烃古温度、浮游有孔虫<14>C年龄、硅藻组合和有机碳含量重建了地表水的温度、盐度、来源和生物生产力。而底栖沉积物的层状保存程度、C/S比值、碳酸盐含量、氧同位素比值则是反映深水环境的指标，可用于重建深水的氧合作用、通风率、溶蚀性和腐蚀性。此外，利用风沙粒度、通量、ESR信号强度、风沙组分中石英的结晶度、矿物成分等反演了西风急流强度、风沙物源和风沙源区的干燥程度。在此基础上，研究了地表水环境、深水环境变化与亚洲季风变化的相位关系。结果基本支持了Tada et al.（1999）的假设，即亚洲夏季风强度的增加增加了长江和中国其他河流的流量，从而使低盐度、高营养度的东海沿岸水向对马海峡入口扩张，增加了东海沿岸水向日本海的流入。这反过来又增强了日本海的海面生产力和密度分层。研究结果还揭示了东海海水进入日本海后，日本海表层温度、表层生产力和深水通风的详细变化。研究结果进一步表明，全新世期间，亚洲季风可能发生了千年尺度的变化，从而导致了日本海古海洋条件的变化。少

This research project aims to 1)reconstruct paleoceanographic changes of the Japan Sea during the last glacial period to Holocene with high time resolution wing multiple cores obtained from the Japan Sea, 2)compare these changes with changes in paleo-monsoon intensity that is estimated from proxies extracted from the same sediment cares, and 3)clarify how the surface and deepwater environment of the Japan Sea responded to the changes in the pattern and intensity of East Asian monsoon.As indicators of the surface water environment, we used oxygen isotope ratio of planktonic foraminifers, alkenone paleatemperature, ^<14>C age of planktonic foraminifera, diatom assemblage, and organic carbon content to reconstruct temperature, salinity, origin, and biological productivity of the surface water. Whereas as indicators of the deepwater environment, degree of lamina preservation, C/S ratio, carbonate content, oxygen isotope ratio of benthic raminifers are used to reconstruct oxygenation, venti … More lation and corrosiveness of the deepwater. In addition, eolian dust grain size, flux, ESR signal intensity and crystallinity of quartz in the eolian dust component, and mineral composition are used to reconstruct westerly jet intensity, provenance of the eolian dust, and degree of dryness in the source areas.Based on these reconstructions, we examined phase relationships among changes in the surface water environment, deepwater environment, and variabilities of Asian monsoon. The results basically support the hypothesis by Tada et al. (1999) that increased intensity of Asian summer monsoon enhanced discharge of Yangtze and other Chinese rivers, consequent expansion of lower salinity and higher nutrient East China Sea Coastal Water to the entrance of the Tsushima Strait, and increased the influx of the East China Sea Coastal Water into the Japan Sea. This in turn enhanced surface productivity and density stratification within the Japan Sea. The results also demonstrated detailed changes of sea surface temperature, surface productivity, and deepwater ventilation in the Japan Sea in response to the intrusion of the East China Coastal Water into the Japan Sea. The results further suggest the possible occurrence of millennial-scale changes in Asian monsoon and consequent changes in paleoceanographic conditions in the Japan Sea during Holocene. Less