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石笋凭借其准确的年代学和对洞穴外界环境的敏感响应,已经成为第四纪研究的重要力量。亚洲季风区轨道-千年尺度石笋δ18O指示亚洲季风强弱的变化,但是在更短的时间尺度上,石笋δ18O则可能受到其他因素的影响,因此近现代、能与器测记录进行对比的石笋记录研究是衔接现代气候与古气候的关键环节。而这关键环节中的关键问题就是确定石笋的沉积年代。寻找一种适合于无生长纹层、低U含量石笋样品的年代方法对于解决石笋沉积年代有着重要的推动作用。本研究选择广西桂林茅茅头大岩一正在生长的年轻石笋。由于低U含量、高232 Th含量,U系-230 Th定年不成功。利用210Pb定年计算出平均沉积速率为1.96±0.23mm/a,但由于多层晶间孔隙的存在,计算结果偏小。由于石笋中14 C基本为核爆产生,AMS 14 C测试结果计算石笋平均沉积速率为2.10mm/a,但由于未测量到核爆前14 C数据,其值可能仍偏小。由于前人研究指出桂林地区石笋记录能记录夏季风降水,结合桂林多年降水数据,综合计算出该石笋平均沉积速率为2.44mm/a,生长时限为2009—1968年。平均沉积速率和沉积时代的确定,为后续的石笋现代气候研究,进而与古气候衔接提供了重要的研究基础。 相似文献
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Chen Chaojun Yuan Daoxian Cheng Hai Yu Tsailuen Shen Chuanchou Edwards R. Lawrence Wu Yao Xiao Siya Zhang Jian Wang Tao Huang Ran Liu Ziqi Li Tingyong Li Junyun 《中国科学:地球科学(英文版)》2021,64(10):1761-1773
It is conducive to the sustainable development of human beings in karst regions to research the mechanism of karst rocky desertification(KRD) expansion. Whether the large-scale KRD in southwestern China is caused by climate change or human activities is still controversial. In this study, the evolution of the KRD in southwestern China over the past 2000 years was reconstructed through the high-precision δ~(13) C record of stalagmites from Shijiangjun(SJJ) Cave, Guizhou Province, China. Theδ~(13) C of the stalagmites from SJJ Cave exhibited heavy values from the Medieval Warm Period(MWP) to the Little Ice Age(LIA). Furthermore, the δ~(13) C records of other stalagmites and tufa from southwestern China also showed the same significant heavy trend. Because the stalagmite δ~(13) C could record the change of ecological environment, it indicated that the consistent change of the stalagmites δ~(13) C may record the process of KRD expansion in the karst regions of southwestern China. During the MWP, the stronger Asian summer monsoon and the northward movement of the rain belt led to a dry period in southwestern China and a wet period in northern China. In contrast, it was wet in southwestern China and dry in northern China during the LIA.In addition, after the Jing-Kang event(JK event, AD1127) occurred at the end of the Northern Song dynasty, the political and economic center of China migrated to southern China for the first time, which changed the population distribution pattern of larger population in the north and smaller population in the south. Therefore, the expansion of KRD in southwestern China was exacerbated in the MWP due to the change of climate in southwestern China, the migration of a large number of people, wars, the large-scale reclamation of arable land, and the cultivation of large areas of crops. 相似文献
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