中亚昭苏黄土剖面粒度记录的末次冰期以来气候变化历史

History of Climate Change Recorded by Grain Size at the Zhaosu Loess Section in the Central Asia since the Last Glacial Period

对处于西风区的中亚昭苏黄土进行了粒度分析,重建了末次冰期以来的气候环境变化历史。粒度分析表明,昭苏黄土粉砂粒级含量最高,平均含量接近78%,黏土粒级次之,砂粒含量最低,具有典型的风尘堆积特征。剖面粒径>63μm含量变化能与格陵兰冰芯进行良好对比,记录了Heinrich事件和Younger Dryas冷事件及D-O旋回等具有全球意义的气候波动事件,揭示中亚地区末次冰期以来的气候变化具有全球特征。

The Ili region is located in the northeastern part of Central Asian region,dominated by the westerlies all the year round,loess sediments are widely distributed in the piedmonts of Tianshan Mountains and river terraces,which enables the Ili region to be one of the ideal places for the studies on Asian interior aridification,dust sources of the Northern Hemisphere,past atmospheric circulation,and past global climate change.In this paper,we reconstruct the history of climate change since the last glaciation by analyzing the grain size of Zhaosu section loess.The result shows that the content of grain size63 μm can be well compared with the records of Greenland ice core that the climate fluctuations of the global significance such as Heinrich events and the Younger Dryas cold event as well as D-O cycles,reveals the Central Asian＇s climate changes with the global features of millennial scale and high frequency oscillation since the last glaciation. The analysis of grain size indicates that the loess grain size distribution of the Ili region is similar to that of the Chinese Loess Plateau,dominated mainly by silt,but the contents of sand in the Ili loess is lower and fine clay higher,which is different from those of the Chinese Loess Plateau.However,compared with the Chinese Loess Plateau,the overall integrated condition of water and heat in the Ili region is poorer than that of the Loess Plateau,which basically can be concluded that4 μm grain size fraction in the Ili loess may be mainly derived from the Central Desert region,only very small part of the clay results from the role of weathering and pedogenesis or debris.Therefore,given the regional topography and circulation conditions,the dust sources may be mainly from its western desert region of Central Asia,the annually prevalent westerlies and distal dust may play an important role in the formation of the Ili loess. According to the variations of the content of the loess grain size,the Ili region＇s climate change can be divided into four stages since the last glaciation：（74 ~ 60.2 ka） cold period,（60.2 ~ 30.4 ka） warm period,（30.4 ~ 11 ka） cold period and 11 ka warm and dry period.The abrupt climate events reflected from changes in atmospheric circulation revealed by loess grain size at the Zhaosu section loess can be well compared with the Heinrich events and the Younger Dryas cold event as well as D-O cycles revealed by the oxygen isotope records from GISP2 since the last glaciation,suggesting that the Ili region dominated westerlies is likely to be a simultaneous change with the high latitude climate of the Northern Hemisphere since the last glacial period.