洛川黄土记录的最近2500ka东亚冬夏季风变化周期

Periodicity of East Asian Winter and Summer Monsoon Variation during the Past 2500 ka Recorded by Loess Deposits at Luochuan on the Central Chinese Loess Plateau

对厚约140m的陕西洛川坡头村黄土剖面进行间距3～10cm的系统采样,测量了全部样品的磁化率和粒度。选择>30μm颗粒百分含量和磁化率分别作为东亚冬、夏季风强度变化的替代性指标,以新建立的时间标尺为基础,分析了最近2500ka以来东亚季风变化的周期特征。结果表明,第四纪东亚冬、夏季风变化时间序列包含有100ka、41ka和23ka地球运动轨道要素变化的周期,同时包含有约80ka、56ka和30ka的周期。季风变化周期表现为阶段性演化和在同一阶段冬、夏季风变化周期常常不同的特征。这些结果说明第四纪东亚季风变化既与地球轨道要素变化有关,也与季风系统内其它因素变化有关。

The typical loess profile at Potou on the central Chinese loess plateau was sampled at 3-10 cm intervals. All samples were measured for magnetic susceptibility and grain size. The magnetic susceptibility and percentage of the >30 um grain size fraction were used as indicators of summer and winter monsoon strengths respectively, and on the basis of a new reliable time scale, a time series of paleomonsoonal climate variation in East Asia was set up. Spectral analysis for the new time series presents the 100 ka, 41 ka and 23 ka cycles of variations of the orbital elements of the Earth movement. Meanwhile, other cycles such as 80 ka, 56 ka and 30 ka were also recorded in the loess-paleosol sequences unambiguously. The cycles of paleomonsoonal variations during the Quaternary evolved with time, and those of winter and summer monsoons were different in some stages. The variations of the orbital elements of the Earth were not the only dominant factor which triggered cycles of the East Asian monsoonal changes during the Pleistocene, and other factors within the monsoonal system were also important. In addition, the cycles of summer and winter monsoon variations during the past 2500 ka and relationships between them are multimod-el.