Transitional Patterns of YD and 8.2 ka Event Recorded by Annually-laminated Stalagmites from Qingtian Cave, Mt. Shennongjia

Key words: 
• annually-laminated stalagmites /
• Asian monsoon /
• Younger Dryas event /
• 8.2 ka event /
• transitional pattern

Abstract: High-resolution δ¹⁸O records from two annually-laminated stalagmites(QT16 and QT40) from Qingtian Cave, Mt. Shengnongjia reveal a detailed Asian monsoon(AM) variability throughout the Younger Dryas(YD) and the 8.2 ka event. During the mid-YD, the AM variability exhibits three centennial oscillations, while the 8.2 ka event is characterized by two 20-year weak AM events separated by one 40-year AM strengthening event. The general pattern of AM variability in two time windows at this site agree well with other cave records from the AM area and the Greenland records. To quantitatively evaluate the structure of the YD and 8.2 ka event, two mathematical methods are applied. In these analyses, both climate events show an asymmetrical structure, i.e., a gradual transition into the event and an abrupt ending. These transitional patterns are further supported by previous stalagmite records in the AM area. However, the AM changes during these events are significantly different from the temperature changes over the Greenland. To some degree, the gradual AM decline at the onset is similarly reflected by low-latitude terrestrial or oceanic records regarding their onsets. This implicates that a forcing factor associated with hydrological circulations in the tropical ocean might modulate the AM evolution during these events.