DO18 Event Depicted by a High-resolution Stalagmite Record from Yongxing Cave,Hubei Province
ZHANG WeiHong;LIAO ZeBo;CHEN ShiTao;SHAO QingFeng;DUAN FuCai;ZHU LiDong;WANG TianYang;College of Geography and Environmental Sciences,Zhejiang Normal University;College of Geography Science,Nanjing Normal University;
It helps further understand and test forcing mechanisms behind millennial-scale events to decipher their regional responses and structures during the periods of large ice sheets. Using 323 stable oxygen isotope ratios and 5230 Th ages of a stalagmite in Yongxing Cave,central China,we reconstruct a detailed history of the East Asian hydrological cycle during the time span surrounding the Dansgaard-Oeschger( DO) 18 event. The calcite δ18 O profile,together with another two stalagmite records from the same cave,shows a rapid decrease of 1.5‰ at ～ 64.7 ka,confirming the occurrence of DO18 in the East Asian monsoon( EAM) region. The ending limb of DO18 in the EAM regime is characterized by five centennial-scale monsoon enhancing events,and finally culminates at ～ 63. 0 ka. Divergent from a rapid temperature increasing followed by a similarly rapid cooling( ～ 60 a) back to stadial environments of the Greenland DO18 event,the DO18 event in the monsoon region exhibits a significant asymmetric feature with a sharp EAM strengthening but then a smoothing,lasting 1 500 a,decrease. Nonetheless,our stalagmite δ18 O records mirror,in shape and timing,the variations of Atlantic meridional overturning circulation( AMOC) estimated by the ratio of231 Pa/230 Th and recovered from the deep western North Atlantic. This similarity suggests that the AMOC played an important role in regulating the DO18 event in the EAM region. On the other hand,the discrepancy in the pattern of DO18 between the EAM and the North Atlantic climate systems can be attributed to the different regional response to the AMOC change in the high-and low-latitude climate systems. Spectral analysis of the stalagmite δ18 O record denotes significant cycles at the 90% confidence level at 208,150,52 and 14-12 a,close to the previously reported solar cycles at 207,149,57 and 11 a. This consistency of cyclical variabilities between the EASM intensity and solar activity might indicate that solar forcing of centennial-and decadal-scale EASM variation still existed during the MIS4 interval with larger ice volumes.