南海沉积物漫反射光谱反映的220ka以来东亚夏季风变迁

对南海越南岸外“太阳号”95航次17954孔220ka以来的沉积样品进行了漫反射光谱分析, 并从中提取F1和F2两个主因子及亮度和红度等漫反射光谱特征值, 发现漫反射光谱F1值和亮度反映了沉积物中的碳酸盐含量, 而漫反射光谱F2值和红度反映了沉积物中的铁氧化物含量, 后者可用作东亚夏季风的替代性指标.17954孔沉积物的漫反射光谱F2值显示, 倒数第二次冰消期东亚夏季风快速增长时间约在129ka; 本次工作还发现东亚夏季风在两次冰消期前的氧同位素2阶段和6阶段晚期各有一个异常强盛的时期.漫反射分析结果显示东亚夏季风主要受控于太阳辐射强度变化, 并明显地受低纬地区气候的影响. 

Visible Reflectance Record of South China Sea Sediments during the Past 220 ka and Its Implications for East Asian Monsoon Variation

The East Asian monsoon (EAM) is an integral part of the global climatic system. Comparison between marine and terrestrial records can improve our knowledge of the monsoon system and how it responds to changing global conditions. In this paper, reflectance spectroscopy analysis is used to characterize the sediments in core 17954, taken from the South China Sea and representing the past 220 ka. The results show that sediment brightness (factor 1) seems to reflect carbonate contents and its changes are similar to the benthic oxygen isotope. Sediment redness (factor 2), which is related to iron oxide content, seems to monitor paleoclimatic changes in the core. Iron oxide appears to be eroded from catchments and is transported by fluvial means into the SCS. Thus, redness increases (factor 2 decreases) at times of increased precipitation, that is, as monsoon strength increases. Our results indicate that the Monsoon Termination Ⅱ occurred at ca. 129 ka based on orbital chronology. Two abnormally strong summer events occurred at the intervals just before the last two terminations, which are confirmed by other records around the world. A time series anlaysis of the factor 2 record indicates a half-precession frequency, which may correlate with the abnormally strong summer monsoon events, suggesting that the tropical ocean had a major effect on the East Asian summer monsoon.