摘要
首次提出用石笋中稳定同位素记录重建由降雨量和降水气团同位素组成所反映的古气候历史，从而为研究高分辨率的古季风气候信息开辟了新的途径。利用Ｈｅｎｄｙ准则、洞穴温度、研究区水系的δ１８ＯＨ２Ｏ值以及温度公式，证实了同位素分析结果的可靠性，ＣａＣＯ３－Ｈ２Ｏ之间存在同位素平衡分馏。对采自石花洞的石笋样品进行了分辨率约为２５ａ的δ１８Ｏ和δ１３Ｃ的分析测量，从而得到３０００ａ以来。
Unlike low resolution (>1 000 years) δ 18 O record which mostly indicates temperature change in the past, variations of high resolution (<100 years) δ 18 O record of stalgmite mainly reflect changes in rainfall and the isotopic compition of moisture source in the study area. The δ 13 C value of speleothem is mainly controlled by isotope composition of soil CO 2that consists of isotopic composition of C 3and C 4plants. The C 3/C 4ratio is strongly correlated with climatic change. When the δ 18 O and δ 13 C shift to more negative values, the ratio of C 3/C 4indicates wet climate increased precipitation, development of forest. All those climatic conditions may indicate summer monsoon strengthening in the study area. This thoutht provides a new approach to reconstruct high resolution paleomonsoon records. We have first demonstrated this new idea throughout a series studies in Shihua Cave, Beijing. A 12.5cm stalagmite was subsampled at 1mm interval (～25 years resolution) and 109 samples were collected for δ 18 O and δ 13 C analyses. Using Hendy rule, cave temperature and δ 18 O H 2O , we have illustrated the isotopic equilibrium between precipitated calcite and its parent solution and the reliability of our measurement. The δ 18 O and δ 13 C records provide climatic information during the past 3 000 years in Beijing. Our results show that there are six apparently climatic cycles during the last 3 000 years in Beijing. The wet periods were peaked at 2 860, 2 350, 1 850, 1 480, 790 and 150 yr B.P., respectively, with a time step about 500 years. After 600 yr B.P. , all of the δ 13 C values show much heaiver than 3ka mean values. We suspect that this change in C 3/C 4ratio (de forest) was influenced by human activity also. There is a good agreement in the comparisons of the paleoclimate interpreted from the speeothem δ 18 O and δ 13 C records with historical records of temperature and precipitation in Beijing, and precipitation in North Central China reconstructed from tree ring study in Huashan Mountain. Climate in Beijing during the last 500 years, was strongly influenced by the Little Ice Age event which had been found as a global climatic event. In Beijing the climate was relativly arid during the early period of the Little Ice Age. The climate became wetter after 400 yr B.P. and reached a maximum moisture for the 3 000 yr period at ～ 150 yr B.P. Since 100 yr B.P., the climate has become arid again.
出处
《地震地质》
EI
CSCD
北大核心
1997年第1期77-86,共10页
Seismology and Geology
关键词
古气候
古环境分析
稳定同位素
石花洞
石笋
Palaeoclimate
Paleoenvironmental analysis
Stable isotope
Beijing
