History Of Holocene Sandstorm Activity In Qinghai Lake Revealed By High-resolution Photoluminescence Chronology

Qinghai Lake is situated in the northeastern Qinghai-Tibetan Plateau(NETP),where is the junction of couples of major atmospheric systems,i.e.,the East Asian summer monsoon(EASM)and East Asian winter monsoon(EAWM),the Indian summer monsoon(ISM),and the Westerlies.Owing to its unique geological and climatic setting,Qinghai Lake has long been a hot spot for the palaeoclimatic research.Meanwhile,aeolian sediment is widely distributed in the Qinghai Lake Basin,and has been extensively investigated in many studies.However,the aeolian accumulation history during the Holocene is still unclear due to the lack of high-resolution and robust chronology.In this study,high-resolution optically stimulated luminescence(OSL)dating has been applied to set up a robust chronological framework for an aeolian sediments sequence(QH-18)from the south of the Qinghai Lake basin.Combined with multiple proxies,such as grain size,magnetic susceptibility(MS),n-alkanes,the Holocene aeolian accumulation and the possible controlling factors at the study site have been discussed.The results show that:(1)The quartz OSL dating is able to provide high-resolution and reliable chronology for the loess in the Qinghai Lake basin.(2)The loess accumulation commenced since the last deglaciation and continued during the entire Holocene(?14.6-0.5 ka).It is noteworthy that the accumulation rate between-6 ka and 2 ka was significant low compared with the periods from 14 ka to 6 ka and after?2 ka.It is considered that the warmest and wettest regional climate conditions led to the weak aeolian activity and extremely low deposition flux during the middle Holocene.(3)The end-member(EM)analysis of grain-size distribution in QH-18 yielded an optimal model with three Ems,i.e.,EMI(Background dust),EM2(A fraction of medium or long distance transportation)and EM3(A fraction from proximal or local source).The EM3 fraction can only be transported with saltation process in short distances that derived from proximal or local sources.According to the variation and contribution of the Ems,we concluded that the Holocene aeolian activity in the Lake Qinghai basin is likely to be modulated by the lake-level fluctuations of Lake Qinghai,in the way of changing the supply of sandy materials.(4)This study provided a new high-resolution chronological evidence for the study of the aeolian activity history,also has a great significance to the research of climate change.