Century-scale monsoon climate fluctuations from a stalagmite recorded during the middle Holocene Epoch in Hulu cave of Huaping county, Yunnan

A 1875-year (6060-4185 a BP) high resolution time sequence recording the Southwest Monsoon climate changes was established from a stalagmite (FL4), Hulu cave, Huaping, China, on the basis of ICP-MS-230Th series dating and Carbon and Oxygen isotope analysis. Three century-scale events of monsoon weakening in the Middle Holocene (6060-4185 a BP) were recorded, accompanied by three drought events that occurred during 6060-5950 a BP, 5380-5140 a BP and 4810-4620 a BP, respectively, lasting for 90~240 years. Carbon isotope data suggested 5497-5442 a BP and 4210-4185 a BP witnessed two events of heavy rainfall, with a duration from 25 years to 55 years. It is obvious that the events of monsoon weakening and heavy rainfall were controlled by the drive of insolation. Carbon and Oxygen isotope records, with the resolution of 3~10a on average, indicated that a series of decadal-scale abrupt climate changes were superimposed upon the century-scale monsoon climate changes, carrying the characteristic of indentation. The short time-scale of the monsoon climate fluctuations were similar to the Δ~(14)C of growth ring and ice cores, demonstrating that monsoon climate changes recorded by stalagmites in lower latitude areas are comparable to the climate changes in the Arctic Regions. Monsoon climate might be mainly influenced by the strength of insolation in low and middle latitude areas and the General Circulation of the Northern Hemisphere. It is the changes of the strength of insolation that controls the evolution of Indian Monsoon. Stalagmite records reflected that rapid strengthening or weakening of Indian monsoon and century-scale climates fluctuations resulted from the changes of insolation strength.