末次冰期晚期黄土高原西部万象洞高分辨率石笋δ~(13)C记录时频分析

运用小波分析与传统谱分析技术相结合的手段,对典型季风系统交互作用的青藏高原与黄土高原过渡带-甘肃陇南万象洞WX40D石笋616个碳同位素时间序列进行了周期谱演化分析。结果表明:在23-28.3kaB.P期间,石笋碳同位素记录的小波变换系数波谱在频率域尺度其主要的变化周期为120年,200年,并隐约表现出300年和600年的周期;小波变换实部时频分析图显示清晰的能量集中中心有10个,分别为1(23613,197)、2(24000,220)、3(24298,300)、4(25354,222)、5(25565,95)、6(26239,606)、7(26792,115)、8(27085,116)、9(27388,136)、10(27853,177),表明石笋碳同位素记录的古植被演化在该时间段具有明显的5次转变。小波实部过程线分析表明万象洞石笋在末次冰期晚期存在多尺度的变化特征,大尺度的周期变化嵌套小尺度的周期变化。

Time-frequency analysis of carbon isotope record of stalagmite from Wanxiang Cave,western Loess Plateau,during the late of last Glacial

Based on wavelet analysis and tranditional spectral analysis,the carbon isotope records of WX40D stalagmite during 23-28.3ka B.P from Wanxiang Cave between the Qinghai-Tibetan plateau and the Chinese Loess Plateau in Wudu Country,Gansu province,China have been analyzed.The results show that major cycles of carbon isotope record of WX40D stalagmite are 120a,200a and the weak cycle is 300a,600a on frequency scale using wavelet coefficient transformation technique.The time-frequency distribution of wavelet transform coefficient of carbon isotope record indicates 10 energy focus centers: 1(23613,197),2(24000,220),3(24298,300),4(25354,222),5(25565,95),6(26239,606),7(26792,115),8(27085,116),9(27388,136) and 10(27853,177),which reflects a clear palaeo-vegetation evolution history and can also recognize the palaeo-vegetation jump points.The wavelet transformation also shows that the carbon isotope record of stalagmite has multi-scale change characters,one big-scale cycle usually contains several small-scale cycle variations.The wavelet transform can effectively deal with the overlying palaeo-climate information,reduce artificial errors.