倒二冰期以来中亚黄土记录的千年尺度气候变化研究

The study of millennial-scale climate oscillations has received widespread attention due to climate severe and rapid changes during then. The oscillation is significantly forced by North Atlantic Deep Water variations and propagated on a global scale by atmospheric and oceanic circulations. In past decades, the studies on Asian Monsoon provided abundant and high quality geological recorders to help us understanding their amplitude, structure, time, periodicity, and so on. Contrasting, the researchers paid less attention on in westerlies dominated Asia, and it restricted our understanding of the propagation of oscillations signals from Northern Atlantic Ocean to Asia. In this study, we plan to study on millennial scale climate oscillations in Central Asia, and select Darri Kalon (DK) section as research object. Our study will include that:.Construct chronological framework. Optical Stimulated Luminescence dating technology will be selected to construct chronological framework. Although, quartz grains have shown several problems when apply OSL dating in Central Asian loess, potassium feldspar (K-feldspar) is an alternative choice. The Infrared Stimulated Luminescence (IRSL) signal observed at an elevated temperature following a prior infrared (IR) stimulation at 50℃ is more stable and has a much lower fading rate which can lead to more accurate dating data. .Recover moisture evolution history during last two glaciation. In this study, surface samples will be collected in Tajikistan according to precipitation change and investigated their magnetic characteristics. By comparison the relationship between magnetic parameters and precipitation, the ideal proxy of precipitation will be selected. Basing on chronology and proxy data, moisture evolution history of last two glacial will be recovered in Central Asia. .Recover westerlies evolution history during last two glaciation. According to method of Sun (2006), the westerlies components of each sample will be calculated. Combine with chronology, westerlies evolution history of last two glacial will be recovered in Central Asia..Understanding propagation of millennial-scale climatic signals in Central Asia. By comparison amplitude, time, and periodicity of recovered climate evolution curves in Central Asia, Chinese Loess Plateau, and North Atlantic Ocean, the propagation of millennial-scale climatic signals in Central Asia will be discussion..After all, this work will provide more evidences to help us understanding the propagation of millennium oscillation from North Atlantic Ocean to Asia.

亚洲西风区关于千年尺度气候振荡的研究较少，制约了学者们对该事件在亚洲地区传输机制的全面认识，这使得在亚洲西风区开展高分辨率的古气候重建工作显得十分重要。项目以塔吉克斯坦黄土剖面为研究对象，通过pIRIR钾长石释光测年，建立倒二冰期以来黄土年代序列；结合磁学参数恢复中亚地区湿度变化历史；利用波谱分析法分析记录中所含千年尺度气候振荡信号的变化幅度、出现周期，及周期的稳定性；将倒二冰期气候记录与末次冰期对比，检验这些气候事件的重现性。同时，利用数学方法分解黄土沉积粒度组成，提取指示西风环流的粒度指标。将末次冰期中亚地区湿度与西风环流强度变化历史对比，理解中亚地区千年尺度气候振荡与北大西洋地区的气候联系；与季风区记录对比，分析不同气候序列中千年尺度气候振荡信号的强度和发生频率的差异，理解亚洲千年尺度气候波动的传输机制。项目的开展对于理解冰期突发气候事件时亚洲地区的气候格局具有重要意义。

亚洲内陆西风区关于千年尺度气候振荡的研究较少，制约了学者对该事件在亚洲地区传输机质的全面认识。本研究对倒二冰期以来塔吉克斯坦DK黄土剖面的磁学和粒度记录进行了系统调查。岩石磁学调查发现该剖面的磁化率变化规律遵循“成壤”模式，即原生强磁性矿物浓度低、变化稳定，次生强磁性矿物浓度高、波动幅度大，新生成的纳米级磁铁矿主要反映区域降水量。反映纳米级磁铁矿浓度的频率磁化率在末次冰期和间冰期记录了22个D-O事件和5个Heinrich事件。相比较而言，粒度记录的Heinrich事件十分明显，而D-O事件则较弱。这明显区别于黄土高原高分辨率的黄土记录，后者的粒度记录中D-O事件明显，而磁学记录中D-O事件不明显。现代过程和数值模拟研究得出末次冰期时冬春季降水的振荡幅度显著高于夏秋季，而塔吉克斯坦地区降水主要发生在冬春季，而沙尘暴主要出现在夏秋季，与黄土高原相反。由此可知，塔吉克斯坦黄土的磁学记录主要反映的是冬春季的降水信号，粒度则反映的是夏秋季的沙尘活动。结合石英释光年代进一步得出，塔吉克斯坦地区在冰阶时干旱但粉尘活动弱；而在间冰阶时该湿润但粉尘活动较强。但这种特殊的气候演化模态仅存在于冰期模态。在末次间冰期，塔吉克斯坦地区的气候变化规律与黄土高原基本一致，其差别主要体现在塔吉克斯坦地区湿度变化滞后约3ka，该结果与伊利盆地的黄土记录基本一致。对比间冰期、冰期、冰盛期时千年尺度气候事件的振幅可以发现，暖期时气候事件（湿度）的振幅大，冷期时气候事件（湿度）的振幅小，即：温度对千年事件中的湿度变化起到一定程度的控制作用。总之，通过中亚黄土的系统调查，不仅扩展了我们对亚洲内陆西风环流的认识，同时也有利于加深了我们对亚洲季风环流的认识。