Holocene Environmental Change And Aeolian Activity History Recorded By Sediments From Lake Tolbo In Mongolia

Altai area in Western Mongolia is mainly controlled by the westerly belt.The evolution history of climate and environment is complex due to complex terrain and circulation factors and unclear indication significance of some substitute indicators,and more records with reliable chronological framework and clear index significance are needed.The desert and Gobi of Mongolia are one of the main sand sources of dust storms in the Central and East Asia.Studying the historical aeolian sand activities in this area is of great significance for understanding the dust accumulation history and circulation background in the northern hemisphere further,but there is still a lack of continuous records of aeolian sand or dust activities.Here we report a sedimentary record using a sediment core from Lake Tolbo(TB19-A,332 cm-long)in northwestern Mongolia,the core was dated using AMS¹⁴C and the reservoir effect was assessed for the chronology.The indicative significance of various environmental proxy indicators is comprehensively analyzed,and the environmental change history of the basin since the late deglaciation and Holocene is understood.Lognormal distribution function and grain size-standard deviation methods were employed to extract the aeolian components in the sediments from the grain size data of the sedimentary sequence for reconstructing the history of regional aeolian sand activities or dust storms.The results show that:The bottom age of TB19-A core is 13.75cal kyr BP.The organic matter in sediments mainly originate from lake algae,and the content of organic matter is closely related to the change of temperature.The element intensity ratio of coarse-grained element Zr and fine-grained element Rb can be the index of precipitation in the basin.The components with median particle size of 15?84?m and>84?m in the sediments of Tolbo lake are suitable indicators of dust storm and regional aeolian sand activity respectively.The conclusions are as follows:(1)There was more precipitation at 10.3-4.8 cal kyr BP in northwestern Mongolia.The precipitation of 4.8-0.3 cal kyr BP is less than the previous stage,and drought exacerbated since 0.3 cal kyr BP.(2)At the late last deglacial(13.75-11.6 cal kyr BP),there were strong local aeolian sand activities in the basin,which may be related to YD cold events.Since Holocene,the change of the local aeolian sand activities in the basin is consistent with regional dust storms in NW Mongolia,which is shown as follows:During the early and middle Holocene in NW Mongolia,aeolian sand activities were generally weak,and relatively strong regional dust storms occurred during the periods of 9.7-8.6 cal kyr BP and 7-6cal kyr BP.After 5 cal kyr BP,local aeolian sand activities and regional dust storms intensified significantly,and both were at high levels until 0.7 cal kyr BP.Extremely strong regional dust storms occurred in the past 0.3 cal kyr BP.There is a significant correlation between aeolian activities and regional environment,and frequent aeolian activities mainly occur in dry periods.(3)The dust storm history in NW Mongolia is similar to those documented in Gonghai Lake in northern China and Bosten Lake in NW China,reflecting the influence of the atmospheric circulation associated with the Siberian High on large-scale aeolian activities in arid regions,specifically,the dust storm activity does increase in northwest Mongolia and North China during the period of high pressure enhancement,but the period of high pressure maximum is not the period of intensest dust storm activity.The changes of the North Atlantic Sea surface temperature,NAO phase and winter solar radiation can change the sand emission potential of the underlying surface,which is an important driving mechanism of aeolian sand activities.Human activities may have also played important roles in the strong dust storms in the past 300 years in addition to natural factors.