RAPID CHANGES IN THE EAST ASIAN MONSOON DURING THE LAST INTERGLACIAL IN THE BOHAI SEA COASTAL ZONE, CHINA

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 &lt; 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.</p

Age of the MGS5 segment of the Milanggouwan stratigraphical section and evolution of the desert environment on a kiloyear scale during the Last Interglacial in China's Salawusu River Valley: Evidence from Rb and Sr contents and ratios

The MGS5 segment of the Milanggouwan stratigraphical section in China&#39;s Salawusu River Valley records 8.5 sedimentary cycles consisting of dune sands alternating with fluviolacustrine facies or/and paleosols. Based on a comprehensive analysis of the distribution of Rb and Sr within the segment and paleoecological evidence (fossils), it appears that the observed sedimentation cycles mainly resulted from fluctuations between dry-cold and warm-humid climates, which indicates that the MGS5 segment experienced at least eight cold-dry and nine warm-humid climatic fluctuations. Of these, 12 cold-warm climate fluctuations correspond to DO20-DO25 and stadia 21-26 recorded by the NGRIP ice cores. Another five cold-warm climatic fluctuations that occurred during MGS5e correspond to five substages (5e1-5e5) recorded by the GRIP ice cores from Greenland. This kind of high-frequency climatic fluctuation on a kiloyear scale was mainly subject to variations in the strength of the East Asian winter and summer monsoons.</p

Climate fluctuation on a kiloyear scale during the Late Last Glacial in Mu Us Desert, China: evidence from Rb and Sr contents and ratios

The MGS2 segment of the Milanggouwan stratigraphical section in China&#39;s Salawusu River Valley records 5.5 sedimentary cycles consisting of dune sands alternating with fluviolacustrine facies or/and palaeosols. The high Rb and Sr contents and low Rb/Sr ratios in the fluviolacustrine facies indicate the presence of a warm and humid climate, and vice versa for a dry and cold climate. Rb and Sr appeared to have 5.5 element cycles that are consistent with the sedimentation changes, and each cycle lasts about 2 ka on average. This study suggests that the observed cycles mainly resulted from variations in the strength of the East Asian winter and summer monsoons, and the MGS2 segment experienced six cold-dry winter monsoons and five warm-humid summer monsoons during the OIS2. In addition, the millennial-scale monsoonal climate fluctuations revealed by the element cycles corresponded well with the Dansgaard-Oeschger cycles recorded in the Greenland ice cores and Heinrich events in the North Atlantic marine sediments. Therefore, the monsoonal climate fluctuations revealed by the Rb and Sr in the MGS2 segment were likely triggered by global climate change.</p

Kiloyear-scale climate events and evolution during the Last Interglacial, Mu Us Desert, China

The fifth segment of the Milanggouwan stratigraphical section (MGS 5) in the Mu Us Desert provides high-resolution geological information on environmental variations during the Last Interglacial. The analysis of grain content (&lt;50 mu m), organic content, SiO2, Al2O3, TOFe, and SiO2-(Al2O3 + TOFe) ratios in the MGS 5 suggest that there were 17 kiloyear-scale climate fluctuations in the Last Interglacial, including 9 warm events (W1-W9) and 8 cold events (C1-C8), dominated by the East Asian summer monsoon and winter monsoon respectively. The analysis also suggests that the Eemian interglacial was unstable, with 3 warm events (W7-W9) and 2 cold events (C7-C8), indicating that climate fluctuations affected the East Asian monsoon in the Mu Us Desert during the Last Interglacial. The change cycles and the nature of the kiloyear-scale climate events have a close temporal relationship with the Greenland ice-core oxygen isotope data, suggesting that the climate forming mechanism was affected by polar weather, North Atlantic sea ice, range of the Eurasian ice front, and movement of the Arctic frontal, all of which affect the intensity of the Siberian-Mongolian high pressure region through the movement of the cold air mass.</p