YAMAMOTO Masanobu Hokkaido University, Graduate School of Environmental Earth Science, Associate Professor, 大学院・地球環境科学研究科, 助教授 (60332475)
YOKOYAMA Yusuke The University of Tokyo, Graduate School of Science, Lecturer, 大学院・理学系研究科, 講師 (10359648)
ITAKI Takuya The University of Tokyo, Graduate School of Science, PD of JSPS, 大学院・理学系研究科, 特別研究員(PD)
|Budget Amount *help
¥11,400,000 (Direct Cost : ¥11,400,000)
Fiscal Year 2004 : ¥4,200,000 (Direct Cost : ¥4,200,000)
Fiscal Year 2003 : ¥7,200,000 (Direct Cost : ¥7,200,000)
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
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