Influences on Asian summer monsoon during Dansgaard-Oeschger events 19 to 25 (70–115 kyr B.P.)

The climate variability during Dansgaard-Oeschger (D-O) events 19 to 25 (first recognized in the Greenland ice cores) was recorded in the Asian monsoon region, but the climatological dynamic mechanism is still poorly understood. Here, we present a new ²³⁰Th absolute chronology and high-resolution record of the Asian summer monsoon (ASM) from 117 to 69 kyr B.P. based on 25 ²³⁰Th ages, 803 oxygen and carbon isotopes, as well as 493 trace element ratios of the YYZ1 stalagmite from Yangzi Cave in Fengdu County, 120 km from Chongqing City, China. The δ¹⁸O record supports a strong ASM during marine isotope stages (MIS) 5a and 5c and a weak ASM during MIS 4, 5b, and 5d. Millennial-scale oscillations of D-O 19–25 were also recorded in our speleothem δ¹⁸O. Multiple environmental proxies, δ¹³C and trace element records of YYZ1 stalagmite can also reflect local climate and environmental changes. A drought event was clearly identified between 93.0 and 91.5 kyr B.P., referred to as the 92 kyr event, which exhibited a rapid and abrupt fluctuation (V-shaped) based on our multi-proxy results. We found that D-O 25 event was not obvious in our record and in other Chinese speleothem records. The D-O 25 event occurred within a period of decreasing North Hemisphere summer insolation (NHSI), which led to different climate backgrounds, e.g., the increase of ice volume and the corresponding weakening of the Northern Atlantic thermohaline circulation. Conversely, the D-O events within the high NHSI period or the warm stages (MIS5a, MIS5c) exhibited more obvious fluctuations than those in the low NHSI period or the cool stages (MIS5b, MIS5d). Thus, we suggest that the differences between D-O events are mainly related to the change of the ASM in response to variable NHSI. Furthermore, the ASM during D-O events was also influenced by climate variations in the Southern Hemisphere (SH) and low latitudes, which should not be ignored.