The Late Quaternary Climate and Environmental Changes of the Southwest China：Stalagmite Carbon and Oxygen Isotope Records From Libo, Guizhou

• Main Authors: Wei-Lin Chung, 鐘瑋琳
• Other Authors: hui-lin lin
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/69pg69

碩士 === 國立中山大學 === 海洋地質及化學研究所 === 97 === Three stalagmites, JSD 01, JSD 02, and L12, were collected from Libo county in the southern Guizhou provence. JSD 01 and JSD 02 are 14cm long stalagmites from Golden Lion Cave and L12 is a 7.1cm long stalagmite from Dragon Spring Cave. Subsamples were drilled along the central axis for JSD 01V while subsamples of JSD 01H were obtained along the horizontal axis. Subsamples were analyzed for carbon and oxygen stable isotopes. The age determination for stalagmites were done by U-Th dating. The JSD 01 dates range from 93,700 to 95,200 yr B.P.; the JSD 02 dates are from 87,900 to 88,200 yr B.P.. The L12 dates are from 750 to 9,560 yr B.P.. The stalagmite record from Golden Lion Cave is correspondent to the marine isotope stage 5 (MIS 5) in age. The δ18O values of stalagmite JSD 01 record in MIS 5c are ranging from -6.58‰ to -5.17‰ ; δ13C values are from -9.19‰ to -6.84‰. Stalagmite JSD 01H records are ranging from -8.11‰ to -5.7‰ for δ18O and from -9.67‰ to -2.46‰ for δ13C. The δ18O values for stalagmite JSD 02 record in MIS 5c are from -8.15‰ to -7.12 ‰ and are from -9.09‰ to -5.19‰ for δ13C. The results indicate a warm and wet climate prevailing during MIS 5c and MIS 5b in Guizhou. An intensification of summer mosoon would increase in precipitation and vegetation above the cave. Result from JSD record shows data obtained from the horizontal axis may be younger in age than vertical axis in terms of sampling direction. The stalagmite L12 contains two sections: (1) Dates range from 700 to 2,400 yr B.P. between top and 35mm: the δ18O values are ranging from -8.23‰ to -7.07‰ while δ13C values are ranging from -11.61‰ to -6.98 ‰; (2) The δ18O values are ranging from -10.52‰ to -7.54‰ and δ13C values are from -10.75‰ to -6.98‰ between 35mm and 71mm. Results suggest a warm and wet climate prevailing during 9,000-9,600, with lighter δ18O values reflecting a strong summer monsoon. A decline of summer monsoon occurred around 9,000 yr B.P. as shown by a sharp increase in the δ18O. This sudden climatic change might lead to a decrease in vegetation and soil loss above the cave, resulting in the cease growth of the stalagmite. Around 2,400 yr B.P. the growth of stalagmite was resumed. The lighter δ13C values and heavier δ18O values represent a cooler and drier climate in late Holocene. After ~1,000 yr BP, a deforestation event occurred in the area probably which was induced by human activity.