摘要
利用Olympus偏光显微镜,直接在光学薄片上对长江中游和尚洞HS 4石笋进行微层计数,并测量微层厚度。微层计数结果与其对应的U Th定年结果相吻合,证明该支石笋微层为年层;统计分析说明,该石笋的年层厚度变化响应近百年来东亚夏季风强度变化,两者呈负相关,说明长江中游石笋生长受东亚夏季风制约。因而,长江中游石笋年层厚度可以作为高分辨率的东亚夏季风强度代用指标。
An active stalagmite, named HS-4, about 240cm long, was collected from the middle reaches of the Yangtze River in April, 2000. The stalagmite HS-4 has been the subject of our study to count growth-layers and their thicknesses. This stalagmite was growing up to the date of it's collection, whose micro-layers reveal typical annual characteristics (Tan Ming et al. Quaternary Sciences,2000,20:391 ), such as clear interface, distinct light and dark lamina. It thus can be an ideal specimen for paleoclimate studies. The comparison of detailed micro-layer (from 0～11cm to the top) counting with the U-Th series dating indicates that the HS-4 layers are annual. The average growth rate of stalagmite HS-4 from 0～6.4cm measured by optical microscopy is 500 μm/a, which is faster than the growth rate of other stalagmites reported in China (Wang Yongjin et al. Science in China(Series D),2002, 45:88～96; Tan Ming et al. Quaternary Sciences,2002, 22:209～219), and the large variation in layer thickness(the thinnest is 125 μm wide while the thickest is 1 250 μm) shows HS-4 layers are sensitive to outside environment. The layer thickness correlates well with the intensity index of the East Asian summer monsoon over the last century. However, high summer monsoon intensity index indicates weak summer monsoon, and low summer monsoon intensity index indicates strong summer monsoon (Shi Neng et al. Journal of Nanjing Institute of Meteorology,1998, 21:208～214), which suggests that there is an negative correlation between the layer thickness of stalagmite HS-4 and the East Asian summer monsoon intensity, and the growth of the stalagmite HS-4 is controlled by the East Asian summer monsoon intensity. The study supports that the layer thickness of specimen HS-4 from the middle reaches of Yangtze River is a high-resolution proxy of the East Asian summer monsoon intensity. Additionally, further research of the long period of the annual layers of HS-4 may be helpful to understand the variation of East Asian summer monsoon intensity through the Holocene. However, the precipitation and temperature act on the stalagmite growth differently (Genty et al.Chemical Geology, 2001,176:191～212; Railsback et al. Journal of Sedimentary Research, 1994,A64:147～155). So although the layer thickness of stalagmite HS-4 is an index of the East Asian summer monsoon intensity, further research is needed if we want to reconstruct the paleotemperature and paleoprecipitation individually
出处
《第四纪研究》
CAS
CSCD
北大核心
2005年第2期228-234,共7页
Quaternary Sciences
基金
国家自然科学基金项目(批准号: 40172060和 40472150)资助
关键词
石笋
年层厚度
东亚夏季风
长江中游
stalagmite, layer thickness, East Asian summer monsoon, middle reaches of the Yangtze River
