A possible Younger Dryas-type event during Asian monsoonal Termination 3

摘要

Seven U-Th dates, 560 δ~(18)O data and microscopic sequences were measured for stalagmites from two high-altitude caves in Shennongjia area, Hubei Province. Variations of the decadal-resolution stalagmite δ~(18)O record from Swan Cave (1600 m elevation) reflect large spatial changes in circulation strength and precipitation of Asian monsoon. The evidence comes from a great similarity among the stalagmite δ~(18)O records from Nanjing, Jiangsu Province; Libo, Guizhou Province and here studied area during the last deglaciation, including a part interval of Younger-Dryas event and Bolling-Allerod. A 30-year-resolution stalagmite δ~(18)O record from Yongxing Cave (1400 m elevation), 70 km away from Swan Cave, reveals a rapid transition of Asian monsoon climate during Termination 3 at about 245±5 kaBP. Based on 3 U-Th dates and about 5000 continuous annual bands, a millennial dry episode has been observed during Asian monsoonal Termination 3 from the Yongxing δ~(18)O profile. With respect to its structure, duration and transition, the dry reversal, as indicated by our stalagmite δ~(18)O record, generally agrees with the pattern of the YD event well-expressed in the Chinese stalagmite δ~(18)O records. This YD-type event is characterized by a large decrease in δ~(18)O value as much as 2.30 per thousand, more than half of the δ~(18)O excursion between glacial/interglacial periods, and lasts 1371 ± 59 a determined by the annual counting chronology. After this event, the monsoon climate shifted abruptly into the interglacial period within 74±4 a. Our data corroborate the view that the repeated occurrence of YD-type event was not an "accident", possibly resulted from the coupling of ice-sheet and oceanic/atmospheric circulations.