A Study Of Environmental Changes In Takermohuer Desert During Late Holocene

Takermohuer desert locate in the west of Yili, Xinjiang of China, which is the typical region strongly influenced by west wind. Because the aqueous vapout carried by west wind drift affect its precipitation, thus it can record the climate change process and model of westerly zone well. Based on the age model constructed with OSL dating results, this paper analyzed the environmental proxies of sediments of Kekdala section which locate in the center of Takermohuer desert, for example grain size, organic carbon, calcium carbonate, magnetic susceptibility, and has been applied to reconstruct the regional climate variability during the late holocene. After comparing the different regional climate change, the present study yielded the primary conclusions as follows:1.Environmental significance of proxies: The characteristics of grain size parameters display that the sediment is composed by three kinds of sand in the section. There is significant correlation between the organic carbon and calcium carbonate, both of which reflect the same climate condition while calcium carbonate reflects different climate condition between westerly and monsoon. Magnetic susceptibility is high value and reflects dry climate in sand horizon; and the case in silty sand or weakened soil horizon is opposite; this characteristic is opposite in monsoon zone. Frequency magnetic susceptibility reflects the same climate condition between westerly and monsoon region.2.Date sequence of the section: The date of the section is assaied by OSL, and according to the assaied OSL date using dating model of grain size and magnetic susceptibility to construct the date sequence of the section. The date of the section bottom is 3.71±0.38ka BP, which indicates that the section is middle and late holocene horizon. Otherwise, the comparison results of date sequence in the present research area are very similar to the other regions.3.The process of climate change: The climate of Takermohuer desert changed frequently during late Holocene and had multiple positive or reverse process(drift sand fixed developing soil or wind sand activated and expanded). The climate was warm-dry in early stage of the period from 3.71 to 3.06ka BP, but it was cool-wet in mid-late period and the weakened paleosol(Se6) was formed. During 3.06 to 2.78ka BP, wind was strong and sand was activated, the plant coverage of desert was very low and the climate windy and warm-dry, then paleosand(E7) was formed. From 2.78 to 2.10ka BP, the wind was weak and stable and sand was moved feebly and the major sediment was fine particle; the climate was cool-wet and maybe changed from warm-dry to cold-wet, then to warm-dry. There were sand paleosol(Se4) and weaken-ed paleosol(Se5) in this period. The wind was weak and the plants coverage of desert was good in the period from 2.10 to 0.50ka BP; the sand was activated weakly and the sediment was very fine sand, and this was a cold-wet stage; there were three sand-paleosol horizons(Se3,Se2,Se1) formed. From 0.50ka BP to the present time, the average wind was strong, the climate was dry which was characterized by cool-wet in prior period and then became warm-dry; in recent 100 years, the climate tended to be warm-dry and the sand was activated strongly, can also be anthropokinetics was a reason of the sand activity.4.The model and mechanism of climate change: The climate's characteristics were warm-dry, cool-wet or cold-wet, which belong to westerly model. Because it was impacted by west wind drift, the precipitation and temperature changes are related to North Atlantic water temperature and North Atlantic Oscillation. The analytical result of climate periodicity displays that it is related to the instability of North Atlantic the rmohaline circulation and the short-scale change of 14C in holocene aerosphere. Bedsides, modulation of Solar and Gleissberg periodicity are also the important factors.