THE RESEARCH OF THE LAYER THICKNESS OF THE STALAGMITE FROM THE MIDDLE REACHES OF THE YANGTZE RIVER TAKEN AS AN PROXY OF THE EAST ASIAN SUMMER MONSOON INTENSITY
An active stalagmite, named HS-4, about 240cm long, was collected from the middle reaches of the Yangtze River in April, 2000. The sralagmite 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 500μm/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 125μm wide while the thickest is 1 250μm) 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.
stalagmitelayer thicknessEast Asian summer monsoonmiddle reaches of the Yangtze River
NETL
NSTL
万方数据
维普
