风成沉积地层化学元素记录的毛乌素沙地气候变化

毛乌素沙地位于东亚季风边缘区，是研究全球气候变化和沙漠变迁的理想场所。选取沙地东缘风成砂/古土壤/湖沼相沉积序列，以常量化学元素含量及比值变化揭示了全新世的气候变化。结果表明：常量化学元素氧化物含量在全剖面上呈SiO₂ > Al₂O₃ > K₂O > Na₂O > Fe₂O₃ > MgO > CaO，且在不同沉积相中含量存在差异；常量化学元素氧化物与<63 μm粉黏组分及磁化率的相关性分析显示，Al₂O₃、Fe₂O₃、MgO三者之间呈显著正相关性，且与粉黏组分、低频磁化率（X_lf）也呈显著正相关性，表明<63 μm粉黏组分、X_lf可以反映夏季风的强弱；全新世气候变化存在多次暖湿冷干波动，10.39 ka BP之前出现3次快速的气候颤动，表现为3层风成砂与3层湖沼相互层沉积，指示存在3次冬夏季风交替变化；10.39~9.34 ka BP、8.68~8.29 ka BP、2.72~1.34 ka BP为3次明显的冬季风势力增强、风沙活动加剧的相对冷干气候；在9.34~8.68 ka BP、8.29~2.72 ka BP、1.34~0.62 ka BP为3次明显的夏季风盛行、降水增多、生草成壤的相对暖湿气候；0.62 ka BP之后与现代气候状况相近。化学元素及其比值反映出毛乌素沙地具有千百年尺度的气候波动，并与北半球其他地区气候变化有着良好的对比。

Climate change of Mu Us Desert revealed by geochemical elements in the aeolian sedimentary stratum

Located in the southeastern depression of the Ordos Plateau and the northwestern edge of the East Asian monsoon, Mu Us Desert is sensitive to climate change and has a vulnerable ecological environment. It has always been an ideal place to research climate change and desert evolution. The Daliuta (DLT) Profile(39°15'14″ N、111°15'08″ E)in Shenmu County, locating in the eastern Mu Us Desert, has developed representative eolian sand-paleosoil or eolian sand-lacustrine sedimentary sequence. Through analyzing the sediments in DLT Profile, based on data of OSL dating, geochemical major element oxides and the ratio of these elements, in combination with magnetic susceptibility, it was revealed that influenced by the East Asian monsoon, the regional climate has warmed overall since the Holocene, while there was still instability. The results showed that:(1) The sediment of DLT Profile is mainly composed of SiO₂ and Al₂O₃, accounting for 69.72%~81.40.and 11.04%~12.71%, respectively; the major element oxides' contents are in order:SiO₂ > Al₂O₃ > K₂O > Na₂O > Fe₂O₃ > MgO > CaO. There are differences among the contents of different sedimentary facies. Chemical activity of different geochemical elements shows obvious variability:K, Na are highly active, easy to enrich under the dry-cold climate and belonging aeolian sand; Ca and Mg are easily enriched in semi-arid and semi-humid areas; Si is relatively stable and contains a large amount in aeolian sand; Fe and Al are less active and enriched in paleosol indicating warm-humid climate. (2) The analysis of the correlation among major element oxides and the <63 μm silt and clay composition and magnetic susceptibility shows that there is a significant positive correlation among silt and clay composition, magnetic susceptibility and Al₂O₃, Fe₂O₃ and MgO; the more the content of silt and clay composition, the easy the Al₂O₃, Fe₂O₃ and MgO adsorbing and enriching, and the high the magnetic susceptibility (X_lf), indicating that the climate is relatively warm and humid; otherwise, it indicates a relatively dry and cold climate. (3) In the southeastern Mu Us Desert, there has been many times of climate change since the Holocene. Before 10.39 ka BP, climate has fluctuated frequently. The characteristics of the profile has showed alternating deposition of aeolian sand and lake-swamp. During 10.39~9.34 ka BP, 8.68~8.29 ka BP and 2.72~1.34 ka BP, winter monsoon had enhanced and cold-dry climate with strong winds had prompted intense aeolian activities so the desert had experienced a strong wind-sand activity period. From 9.34~8.68 ka BP, 8.29~2.72 ka BP and 1.34~0.62 ka BP, under the background of increasing temperature and humidity, sand dunes had fixed and soil had developed. After 0.62 ka BP, the climate has closed to the modern climate. Besides, the differences of geochemical major element oxides and ratio have influenced by winter and summer monsoon of East Asia, reflected the millennium to centuries scale climate change, which is regional response to global climate change.