The Evolution Of The Early Holocene East Asian Monsoon And Its Driving Mechanism

The Asian monsoon climate system plays a vital role in the global climate system,which not only directly affects the geographical environment in the region,but also has an important impact on the surrounding area.Holocene is the period of human being,since the Holocene(about 11.5 ka BP)the earth began to enter the interglacial period,the global climate is more stable than the ice age,but in the early Holocene global climate is still sensitive,because of the existence of Laurentia ice sheet.Therefore,it is important to understand the characteristic of early Holocene climate.For that it is possible to provide a scientific basis for the trend of climate change in the context of global change,especially for the melting of bipolar ice sheets in the context of global warming.In this study,a high-precision and high-resolution East Asian monsoon record describing the climate variability between 11.29 ka and 10.20 ka BP,is reconstructed by 4 high-precision 230Th ages,449 oxygen isotopes and about 1000 layers from a Shihua cave stalagmite,Beijing.This paper discusses the discovery of extremely thin false band in stalagmite from Shihua cave,the phase relation of the monsoon subsystems in the early Holocene Asian monsoon region,the early Holocene weak monsoon events and their driving mechanism.The main conclusions are as follows:(1)By comparing the results of layer counting and the results of MC-ICP MS 230Th,this study finds found that there is a kind of thin false band in a stalagmite from Shihua cave,Beijing.Since this type of thin layer has the characteristic which Tan thinks it is the mark of annual layer,that is,by adjusting the focus from the surface of the thin section into the sample,the lamina will become dark or light.So we think that this characteristic is not the determinant of annual layer,however annual layers will have this kind of characteristic.The preliminary extrapolation of the thin layer may result in two or even strong DOC(dissolved organic carbon)pulses entering the cave due to the two or even large heavy rainfall events(>50 mm/d)during the rainy season.(2)By comparing the record of Shihua cave stalagmite and other high-resolution stalagmites in the Asian monsoon region,we believe that the evolution of the Asian monsoon subsystems in the early Holocene is synchronous.On the orbital scale,The evolution of the Asia monsoon is mainly controlled by the change of solar insolation in the northern hemisphere,and the evolution of the early Holocene Asian monsoon may be affected by the glacial boundary conditions of the northern hemisphere.(3)Four weak monsoon events are identified from stalagmite CS01C oxygen isotope record which detail climate variability between 11.29 ka and 10.20 ka BP.The four weak monsoon events occurr at about 10.9,10.7,10.5 and 10.3 ka BP,respectively.The duration of these four events is about 150 years,130 years,160 years and 80 years respectively.We believe that fresh water outburst and solar activity may be the main cause of the early Holocene weak monsoon events.