Discussion about the Mechanism of the Weak Summer Monsoon Events during the Early Holocence: A case study of precisely dated stalagmite record from Lianhua Cave, Hunan province, China

Key words: 
• Early Holocene /
• weak summer monsoon events /
• stalagmite /
• &delta /
• ¹⁸O /
• Lianhua cave

Abstract: The Early Holocene is an important period of Solar radiation strengthening, global warming and along with ice sheets melting. The cause of the colder events and the weaker summer monsoon in the Asian monsoon region during the Early Holocene has always been the focus of research. It has important significance for the study of the links among the Asian monsoon, ocean and polar regions. Based on 28 U/Th dates and 535 oxygen isotopic data of stalagmite LHD5 from Lianhua Cave, Hunan province, China, a Holocene Asian monsoon evolution record was reconstructed, and the average resolution is 8 year in the Early Holocene. From the LHD5 stalagmite record, the end of Younger Dryas was at 11748±30 a B.P., the start of the Holocene was at 11684±39 a B.P., and the conversion time is about 64 years, which is consistent with the records of the gicc05 ice core from Greenland in the error range. The central age of the six weak summer monsoon events were at 11461±34 a B.P.(1.08‰), 10354±36 a B.P.(0.94‰), 9957±25 a B.P.(0.66‰), 9062±36 a B.P.(0.90‰), 8744±23 a B.P.(0.55‰) and 8144±24 a B.P.(1.02‰) in the record of the stalagmite LHD5 during the Early Holocene, respectively. These weaker summer monsoon events in the Asian monsoon region have a common regional significance. In addition to the 8.2 ka event, the weaker summer monsoon events before 10 ka B.P. were not only affected by the summer insolation but also by the ice-rafted debris (IRD) events in the North Atlantic, but the following weak summer monsoon events were mostly influenced by solar activity and the southward migration of the mean position of the Inter-Tropical Convergence Zone.