西藏安多地区近千年风沙活动过程及对气候变化的响应

Aeolian activity in Amdo Area,and its response to climate change in the last 1000 years

青藏高原历史时期存在广泛的风沙活动,而关于高原中部历史时期的风沙活动的研究较少.本文选择高原中部安多地区柴荣(CR)风成沉积剖面,采用OSL测年方法建立剖面年代序列,以粒度为主要风沙活动代用指标,结合磁化率、碳酸钙、有机质指标,揭示安多地区近千年来风沙活动过程,探讨风沙活动对高原近千年几个气候特征时期的响应,结果表明,安多地区千年来风沙活动可划分为5个阶段:1)1310年以前约300a,风沙活动很弱,气候温暖湿润;2)1310—1660年为气候稳定的过渡阶段,风沙活动较弱,气候相对温暖湿润,其中1450—1570年风沙活动进一步减弱,出现小幅的升温;3)1660—1890年风沙活动强烈,气候寒冷干燥,其中1780—1860年为小冰期中的距今最近一次冷事件;4)1890—1940年风沙活动很弱,进入20世纪暖期的升温阶段;5)1940年至今,风沙活动再次加强,转为冷干的气候环境,但其寒冷程度不及小冰期.柴荣剖面风沙活动所记录近千年气候变化与高原文献记录较为一致,但反映的气候特征事件并不完整.中世纪暖期(持续到1310年)与高原中部、中北部和东北部湖泊具有很好的一致性.小冰期(1660—1890年)的起始时间比高原东北部、西部和中北部反映的晚200~300a,比高原中部的记录晚约150a.小冰期结束时间与整个高原记录一致,其中体现的冷事件与高原其他记录所指示的距今最近的一次冷事件时间相同.20世纪暖期的起始时间与高原其他记录的时间一致,1890—1940年的暖湿阶段和1940年以来的冷干阶段也与高原东北部、西部的研究结果相符.

Aeolian activities are known to exist widely in the Tibetan Plateau in historical periods,about which very little research has been done on the middle plateau.In the present work,aeolian deposition of the Amdo Area CR profile in the middle plateau was investigated.Optically Stimulated Luminescence(OSL)dating was used to establish chronology sequence of CR profiles,and the grain size,magnetic susceptibility,calcium carbonate and organic content of the deposits were analysed to reconstruct the aeolian processes for the last1000 years in the Amdo Area by CR profile.Then,the response to several characteristic climatic periods of the last 1000 years in Tibetan Plateau was discussed.Aeolian activity in Amdo Area during the last 1000 years was found to have experienced 5 stages.About 300 years before 1310,with weak aeolian activity,the profile showed water dynamic action and indicated warm-humid climate.Being a stable transition stage from 1310 to1660,the climate became warm-humid with weak wind from 1450 to 1570,the aeolian activity further weakened with slight warming.The period from 1660-1890 was with cool-dry climate and strong wind.From1780-1860 aeolian activity became more intense and responded with the most recent cold events in the little ice age.From 1890-1940,aeolian activity was very weak,entering the warm period of the 20 th century.From1940,the Aeolian activity strengthened again and the climate became cool-dry,but with much less LIA.The paleo-aeolian depositional record of CR in central Qinghai-Tibet Plateau has a better response to climate change in the last 1000 years,which is consistent with other climate records in different parts of Qinghai-Tibet Plateau.But CR profile cannot completely reflect characteristic climatic events for the last 1000 years.The Medieval Warm Period(until 1310)had good consistency with lacustrine deposits from central,northern and northeastern part of the Qinghai-Tibet.The starting time of the Little Ice Age(1660-1890)is about 200 years later than reflected by the northeastern,western and northen part of the Qinghai-Tibet,and about 150 years later than reflected by the central part of the Qinghai-Tibet.The end time of the Little Ice Age is consistent throughout the whole plateau.The cold event derived from CR profile agreed with the more recent cold event from other records.The starting time of the 20 th century warming period is consistent with other proxy data.Both the warm and wet phase(1890-1940)and the cold and dry period(1940-)showed unanimous agreement with research on the northeastern,western part of the Qinghai-Tibet Plateau.