摘要
用放射性同位素定年方法结合微层计数了解石笋微层的计时特性 ;确定年层的显微图像标志 ;提出矫正石笋层厚时间序列中所包含的沉积趋势的方法 ;建立符合统计要求的层厚量测规则。将石笋年层厚度序列与当地仪器记录的气候要素时间序列进行对比 ,作信号波形分析和统计相关分析 ,找出石笋层厚能够敏感反映的气候要素。如果石笋年层记录的气候信号远强于噪音水平 ,则可利用层厚时间序列重建所敏感反映的气候要素变化历史。利用所建立的方法 ,对北京石花洞石笋进行了实例分析。
Based on comparing TIMS 230 Th dating results with layer counting results, we have verified that many growth layers in stalagmites from China are annual. We found that the most remarkable characteristic for annual layers from the Northern China is their carving like dark division line and convex bright layer in between under microscope. By shifting focus up, the dark line turns to bright line. Such phenomenon is usual to see under a microscope with transmitted light and results from the light reflected by the opaque material in the dark division as long as the layer is not perfectly parallel to transmitted light. Via measuring layer thickness, removing sedimentary trend that formed within the early sedimentary period as the product of deposit geometry and calibrating the layer thickness chronology against meteorological records, we finally establish the layer thickness climatology.\; As an example, the stalagmite TS9501 from Beijing Shihua Cave was selected to do climate reconstruction in this paper. Within the East Asian Monsoon zone, Beijing typically has dry/cold winter and wet/warm summer. Shihua Cave is about 30 km from Beijing downtown and, was opened to tourists in 1986. After that year, CO 2 in the cave air went up from 500×10 -6 to 2?080×10 -6 , and cave temperature went up from about 13 to 15 ℃ (observed data), which resulted in the reduced rate of calcite precipitation. Thus the layer thickness data after 1985 were unavailable. The stalagmite TS9501 contains about 2?650 annual layers and, no evidence of any hiatus in deposition was found. Comparison of variation in annual layer thickness with monthly meteorological data shows a strong link between the layer thickness and the monthly mean temperature (May to August). This is attributable to the high concentration of soil CO 2 within the summer and the signal amplification of geochemical system. The result allows the summer temperature in Beijing extend back to 655 BC with the reconstruction derived from the transfer function T =0.027?53 L +21.855?57 and de trend function y =2.038?3-1.519?7×10 -5 x +7 209?3×10 -11 x 2-1 713 1×10 -16 x 3, where T is summer temperature in ℃ and L the layer thickness in μm. This reconstruction is well agreeable to instrumental and historical records.\;
出处
《第四纪研究》
CAS
CSCD
北大核心
2002年第3期209-219,共11页
Quaternary Sciences
基金
国家自然科学基金 (批准号 :4 0 0 72 0 98)
