Mid-holocene Climate Variation From Lake Evidences Of East Asian Monsoon Margin Areas

The East Asian monsoon margin areas of China are very profit to study the past global environment change because of their sensitivities to the climate changes. Therefore, these areas received intensive attention from paleoclimatologists in recent years. There are a large number of researches on the Holocene climatic variabilities in these areas as yet, but quite different opinions have been expressed as to the climatic conditions of Mid-holocene. Traditionally, the Mid-holocene in most parts of China was thought to be warmer with higher precipitation, resulting from a strong Asian summer monsoon. However, some recent researches have proposed a Mid-holocene drought interval of millennial-scale in East Asian monsoon margin areas. Thus whether Mid-holocene was dry or humid remains an open issue. In this paper, the Mid-holocene (9³Cal kaBP) climate variations and rhythm are reconstructed on the basis of sedimentological and geomorphological data recovered from two series of well-dated lake records. According to the study, we come to some conclusions as follows:1. According to the principle and technology of ¹⁴C dating, researchers found that the reservoir effect on radiocarbon ages is different between peat material and mollusk shells or inorganic carbon in the lake. Dating results of ZYC and QTL section indicate the ages of peat material are almost equal to those of mollusk shells at depth 315cm and 425cm, measured in Chronology Laboratory of Lanzhou University and Chronology laboratory of Peking University, respectively. Accordingly, it seems that reservoir effects of the research region are not evident. Hence the dating results are reliable.2. Based on the reconstruction with multi-proxy records and well-dated data, the climate evolution in the East Asian monsoon margin areas during 9-3 Cal kaBP is divided into four stages: â‘ from cold and dry to warm and humid during the period of 9⁷.8Cal kaBP. â‘¡a significant drought interval of multicentennial scalebetween 7.8-7.5 Cal kaBP. ?Holocene optimum characterized by a warm and moist climate during the period of 7.5⁵Cal kaBP. ?from humid to dry during 5³Cal kaBP.3. Wavelet spectral analysis of C/N^ TOC\ 8I3C\ CaCO3 records of QTL section shows that statistically significant multicentennial and millennial periodicities centered on 512 and 1000 years, which are close to the significant periodicities of residual A14C (reflecting solar activity). These results indicate there is a close relation between climate change of East Asia monsoon margin areas and solar activity. It was supported by the suggestion that climate change in East Asia monsoon margin areas is probably mainly driven by solar activity with two dominant periodicities—512a and 1000a, which was proposed in more and more relative researches.