Study On Climate Change Recorded By Stalagmite Since 14.4ka BP In Lichuan Area

Recently, global climate change has captured worldwide attention in today’s society, and stalagmite because of its high precise chronology and the characteristics of high resolution, it has an important role in the study of the ancient climate change. Based on U/Th absolute dates and stable oxygen isotope analysis data, we have reconstructed Asian monsoon (AM) records over the 14000 years by modern stalagmites from Yulong Cave in Lichuan. The main conclusions we got are here below:The fact that the good replication of δ18O signal between Yulong Cave and others in the AM area during the contemporaneous growth periods indicates that the δ18O signal in these caves are controlled by a common climate fac tor and the δ18O can reveal the AM climate changes on centennial-decadal scales.Stalagmites δ13C value mainly reflects changes in the abundance of vegetation study area, with obvious cyclical characteristics, can be divided into four cycles. Power spectral analysis showed that,δ13C significant period around 2000, probably reflecting the special variation of the local environment of the study area.There is a good correlation between the 513C and gray curves of TCL, showing a significant peak corresponding features, indicating the lithology of sedimentary rocks and δ13C of stalagmites have a good relationship.The correspondence between them confirmed the reliability of δ13C, but also shows the two have a common drive mechanism:When the study area abundant rainfall, lush plants growthed and the soil CO2 production rate increased, while the δ13C negative bias; in this case the particles of soil organic matter content increased, the gray value also increases; and vice versa.Sr/Ca and Ba/Ca with δ13C still have a strong correlation between them, and the Sr/Ca and Ba/Ca change in stalagmite can provide an effective supplement for paleoelimate and paleoenvironment reconstruction. Especially in 5.6ka BP to 4.2ka BP period, Sr/Ca and Ba/Ca decreased significantly and quickly, and δ13C and gray have the same change in this period, indicating that rainfall with vegetation had reduced, and local environment worsen.TCL stalagmite δ18O recorded the "4.2 ka BP weak monsoon events" which corresponding to the north Atlantic cold events, for 4.4ka～4.1ka BP, presents a "two-peak and triple-valley" pattern. Meanwhile, the Yulong Cave records show the increasing trend of East Asian summer monsoon since the Medieval Warm Period (about 1ka BP), while the Indian monsoon enhanced after the ice age (about 0.4ka BP). Therefore Asian summer monsoon enhanced since the last millennium may be affected in different driving factors.