中国科学院地球环境研究所机构知识库

The Bohai Sea coastal zone of China faces the Pacific Ocean to the east and the Eurasian continent to the west; hence, this region is influenced by both the ocean and continental landmasses. The Bohai Sea coastal zone has significant monsoon climate characteristics and a strong sensitivity to climate change. The Miaodao stratigraphical section (MDS) contains historical information about climate features in the region, especially the high-frequency variations during the last interglacial, sea-level changes, and the evolution of the East Asian monsoon. By analyzing the ages of various sedimentary facies in combination with proxy paleoclimatic indices (i.e., grain < 63 mu m fraction, average grain size (Mz), clay + silt/sand content (SC/D), magnetic susceptibility, and the ratios Na2O/Al2O3 and (Al2O3 + TOFe)/SiO2, in the fifth segments of the MDS from the last interglacial (MDS5), we conclude that subsections 5a, 5c, and 5e were controlled by summer monsoons, whereas subsections 5b and 5d were formed when winter monsoons prevailed. These results were similar to oxygen isotope analyses from previous studies including the Spectral Mapping Project (SPECMAP) and the North Greenland Ice Core Project (NorthGRIP). Five and a half comparable oscillations in proxy indices that were dated to ca. 116.1, 118.3, 121.2, 122.7, 125.9, and 128.7 ka occurred within the MDS 5e subsection when winter monsoon winds strengthened. This millennial-scale climate variability during the Eemian period may have reached up to ten and a half oscillations with a quasi-periodicity of approximately a 1,470 year cycle during the late glacial period. This rapid period of climate change has been recorded in northern and central Europe, central Asia, and in East Asia. The climate-influencing mechanism was probably initiated by changes in solar activity and driven by the East Asian monsoon and sea-level oscillations.