中国北方沙漠-黄土体系的沉积和侵蚀过程与未来趋向探析

A perspective on deposition and erosion of the sand-loess system in North China.

中国北方有大面积的土地被沙漠和黄土覆盖,是现代沉积和侵蚀比较活跃的地区。强烈的地表过程不仅影响着区域的生产生活活动,还通过粉尘传输影响北半球甚至于更大范围的气候和环境。长期以来,由于综合研究不够,对沙漠-黄土体系的沉积和侵蚀规律以及未来趋向的认识有限。结合对沙漠沙地-黄土沉积的高密度光释光年代测试结果,基于地统计法和遥感分析的黄土堆积量估算以及现代降尘、地表侵蚀的观察研究,认为沙漠沙地-黄土堆积区的沉积和侵蚀过程受气候变化控制,这里既是堆积区,又是侵蚀区,处于动态变化过程中;黄土比沙地沉积保存着更完整的过去气候变化信息。黄土高原水蚀和风蚀在地质历史时期就存在,人类活动加强了侵蚀过程,但可能还没有实质性地改变这一趋向。通过对地质记录和古气候模拟结果的分析,在未来全球变暖的背景下,沙地地区可能由于有效湿度减少变干而使风尘活动加强,黄土高原地区的粉尘沉积速率也将随之加快。

There is a land of around 1500000 km2 in north China covered by sand and loess deposits,and the sand-loess deposition system is venerable in response to climatic changes and human disturbance.However,to quantificationally separate which one,the climatic change or the human activity,is dominate driver of deposition and erosion of the sand and loess sediments,is still an open question.In this study,we summarize ages of optically stimulated luminescence dating of the sand and loess sediments,employ geostatistic and remote sensing methods,and collect modern observation data of dust fall and surface erosion,to investigate deposition and erosion process in the past,and their possible responses to climatic changes and human activity in the future on the sand-loess system.Based on these interdisciplinary data synthesis,we suggest that climatic change is the most important force to control deposition and erosion of the sand and loess deposits in north China,and that the sand-loess region is both the source and the sink of dust,depending on climate and surface structure.The loess deposit is a more complete palaeoclimatic archive than the sand deposits.The loess erosion in Chinese Loess Plateau commenced in the geological time;the human activity has accelerated the surface erosion,but it did not substantially change the erosion.Under the global warming scenario,the intensified evaporation in the sand-loess region probably may exceed the increase of the monsoon precipitation,causing drying of the sand fields.A drying sand field will strengthen dust activity and increase dust sedimentation rate in the Loess Plateau.