扩扩色勒冰芯污化层记录的青藏高原西部过去100年来大气粉尘的变化特征

Variation of atmospheric dust over the past 100 years recorded by visible dusty layers of the Kuokuosele ice core, western Tibetan Plateau

冰芯粉尘记录是重建大气粉尘特征的良好指标.本文利用慕士塔格山扩扩色勒冰芯污化层重建青藏高原西部近百年来大气环境变化特征.研究发现,污化层等级和污化层厚度比率两个指标与该冰芯Ca^(2+)离子具有较好的一致性,说明其可以作为陆源粉尘的良好指标,为快速获取冰芯大气环境特征提供新手段.污化层比率与中亚粉尘源区和青藏高原北缘粉尘源区的现代沙尘观测记录具有较好的一致性,说明其能够反映近期沙尘事件的变化趋势,冰芯粉尘可能来源于两个源区的共同输入.该地区沙尘天气在1900~2010年间的发生频率呈现逐渐减少的趋势,其原因可能与粉尘源区因降水增多而引起的沙尘事件减少、西风增强引起的局地降水增多,以及青藏高原地面风速减少等方面因素共同作用有关.

Atmospheric dust plays a significant role on regional and global climate change through modifying the radiative balance via changing solar radion, altering the microphysical precipitation process and so on. However, many uncertainties of their climatic effects exist due to obvious regional distribution and short transportation system. The large desert and semi-desert area of Asia, makes this region as one of most severe global dust sources and effecting globally. Glaciers distributed in the Tibetan Plateau contain substantial dust deposition which privide an opportunity to reconstruct past continental aridity and atmospheric circulation. As microparticles, visible dust layers also show excellent potential on environmental exploration. Additionaly, their visible external appearances benefit researchers acquiring both dating and environmental coding as soon as they get the cores. The Kuokuosele ice core was retrieved in 2012 from the Muztagh Ata Mrs. in the eastern Pamir Plateau circumfused by Asian arid regions and deserts. Due to its proximity to the dust sources, the ice core contained clear visible dust layers clearly observed under natural light and floodlight in the cold room by three independent researchers before any sampling process. Two indicators including level （LvoL） and thickness ratio （RvDD of visible dust layers were examined and calculated. Meanwhile, concentrations of Ca2＋ and SO42- were analyzed in order to evaluate the accuracy of observations by naked eyes. The top 52 m ice core was dating to the period of 1900-2012 with ＋1 uncertainty via identifying stratigraphic markers of beta activity and counting seasonal cycles of δ18O and dust layers. The current ice core contains 181 visible dust layers and can be classified to five different levels. Moreover, five-year average RvDL spaned the whole era showed a decreasing trend, and illustrated vivid low values in 1900-1915, 1920-1930, 1990-2010 and high values in 1915-1920. The visible dust layers were then compared with Ca2＋ and SO42- records. To begin with, simultaneous veriation was found between LvDL and two ions. Moreover, RvDL in recent decades was positively correlated with observed records of arid areas of central Asia and northern Tibetan Plateau, suggesting that both sources continuously distributing the for dust deposition in this ice core. Therefore, visible dust layers of the Kuokuosele ice core could be seen as credible excellent medium for study of atmospheric dust deposition, and thus provided an unique opportunity to acquire the enviromental information. In Summary, the entire record of thickness ratio of visible dusty layers in the Kuokuosle ice core revealed a decreasing trend of atmospheric dust over the past 100 year, accompanied by an increasing trend of tempreture expressed by ice-core δ18O and a varied precipitation pattern. Increasing precipitation in the possible source area and the local region caused by the strength of Westerlies might be related to this trend, in addition to this, decreasing wind speeds in the past cannot be ignored.