Early To Mid-holocene Paleoclimatic Changes Recorded By The Stalagmites From The Magou Cave, Henan Province

Magou Cave is located in the transitional area between the hilly area of West Henan Province and Huanghuaihai Plain, Magou Cave formed in Ordovician limestone strata of Juci mountain system in northern Yuzhou city. The study area is a temperate and monsoonal climate zone and mainly affected by winter and summer monsoons. In this paper, we use two stalagmites(MG-1 and MG-40) which were collected from Magou Cave as the research material.Based on 24 accurately dated 230 Th ages and 1988 stable oxygen isotope compositions(?18O) obtained from two stalagmites(MG-1 and MG-40)from Magou Cave, a 2-14 year resolution oxygen isotope profile during the 13.1-4.9ka BP was established, which largely documents the summer monsoon precipitation changes at the cave site. We reconstructed the history of monsoon precipitation during early to mid Holocene, revealed the climate instability of the Holocene Megathermal and also discussed the potential driving forces and dynamics of the ASM in the study region. We also examined the possible links existed between civilization succession and climate change. The followings are the conclusions we obtained in this study:1.The ?18O record of MG-1 and MG-40 show remarkable similarities during the 10.37-7.06 ka BP if we take their resolution difference and dating errors into consideration. The replication of these two records and the similarity to the neighboring cave record suggest that these two stalagmites were most likely deposited under isotopic equilibrium conditions and the oxygen isotope composition of the stalagmite could be used to reconstruct the changes of the precipitation isotope composition. We interpret the stalagmite ?18O from Magou Cave as a qualitative proxy of ASM precipitation, with heavier values indicating a weak ASM and less summer monsoon precipitation, and vice versa, temperature have a minor effect on the speleothem calcite ?18O variations.2.As shown in the Magou ?18O records, summer monsoon precipitation increased during the period from 11.2 to 9.1ka BP and was fluctuated significantly withoutclear trend during the period of 9.1-4.9ka BP. The occurrences of Younger Dryas, 9.3ka and 8.2 ka events in the Magou ?18O profile are in good agreement with other speleothem records from Asian monsoon regions, suggesting that these abrupt events have manifested themselves in the vast monsoon regions at least in East Asian and South Asia during the last deglaciation, and possibly affected by the same driving forces and dynamics. Thirteen significant centennial-decadal weak monsoon events were identified within the period of 8.0-4.9ka BP in the ?18O records of stalagmites MG-1, further confirming the climate instability of the Holocene Megathermal.3.During the 7881-4900 a BP, the MG-1 ?18O record and atmospheric ?14C record have the same periodicities of 83, 36 and 22 years. The MG-1 ?18O record and the NGRIP ?18O record have the common periodicity of 56 year. The 5-7 years periodicities were also found in MG-1 ?18O record, which may be linked to the El Ni?o–Southern Oscillation(ENSO). The concordance of MG-1 ?18O record and atmospheric ?14C record and the NGRIP ?18O record(during the period of 9100-4900 a BP), as well as the spectrum analysis, reveal that not only did both changes in solar radiation and climatic changes at high northern latitude affect the Asian summer monsoon variations during the Holocene, bout also ENSO and the internal interaction of climate sub-systems have significant impacts on East Asian summer monsoon changes.4.The flourishing of the Yangshao Culture at the central China during the 7200 a BP-6000 a BP was coincident with the relatively stable warm-humid climate within the Holocene Megathermal. It is then not implausible that the climate optimum plays an important role in the development of earlier civilizations(e.g., Yangshao Culture).