| To predict the evolution of climate in the future, it is important to explore and analyze the processes and mechanism of the climate system over the past 2000 years. Here the author uses two stalagmites (NO. SN with 255mm and BF1 with 212mm in height) from Xiniu Cave, Shennongjia to investigate a decadal-century scale climatic changes of East Asian monsoon covering the most part of the last two millenary. Based on 16 230Th dating ages and 1187 data of stable isotopic compositions as well as annual laminated sequences of the stalagmites, the author firstly presents the climate records of the past 2000 years in Shennongjia region. By comparing the stalagmite record with historical records, lake sediments and pollen data, the author analyzes comparability and differences of climate change in East Asia monsoon area and preliminarily investigates driven forces of climate change.A time scale of the sample SN has been reconstructed by a polynomial fitting with 9 dated ages and further tested by annual band counting results. In general, the fitting polynomial line is consistent with the annual band growth rate except for that the bottom part of the stalagmite (a height between 196 to 255mm from the top). However, a time scale of the sample BF1 has been established by the annual band counting chronology bracketed with 7 Th-230 dates. The two chronologies from the different age-determination for the two stalagmites agree well in anuncertain of 30 years if using the same 18O signals as tie points.A linear regression between 18O of precipitation and in situ temperature in the adjacent regions shows that a temperature-dependent 18O gradient coefficient is d18O/T=0.64%/ C. Using the gradient coefficient, the author estimated that there is the maximum amplitude of 3.5 C in temperature over the past 2000 years in shennongjia region. The 18O proxy climatic time series can be divided into seven cold/warm cycles. The 18O record displays two warm periods with a relative cold event during the Medieval Warm Period, and that is quite different from other records in the studied area. The Little Ice Age indicated by the 18O curve is divided into five cold valleys and four warm peaks. During Donghan Dynasty, the 18O record of stalagmite, the same as all of temperature records in the East Asia monsoon area, shows a significant warming up trend that is different from other records. During the Medieval Warm Period, the lasting time is shorter and shorter from the south to the north in china, and the east china is more obvious than the central china; the beginning time of the Little Ice Age in shennongjia region (1480aAD) is later than that in other regions (1420aAD), but they all display a persistent decrease process of temperature.Both the annual banding growth rate curve and grey level curve show the evolution processes of the precipitation over the past 2000 years this region and that divide into seven dry/wet cycles. By comparing precipitation proxies of the shennongjia region with the dry/wet records in other regions, the author finds that the long-term change trend of all records is approximately consistent. All records show the characteristics of high precipitation and large swing before 1100aAD, but the characteristics of low precipitation and small swing after 1100aAD. During the Medieval Warm Period there is a very dry period. During the Little Ice Age precipitation is little. Due to different resolution, every record has difference in detail and also reflects area character. By comparing I8O curve with annual growth rate and grey level curve in the stalagmite during the same period, the author brings forward that that climate in shennongjia region mostly embodies matching modes of warm/wet, cold/dry over the past 2000 years, but temperature was out of harmony with precipitation in the course of climate transforming, which shows that shennongjia climateembodies matching modes of cold/wet, warm/dry at part period of time.There are inconsistent between the two stalagmites δ13C curve vs. age due to the cave sy... |
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