冰芯所记录的环境变化及空间耦合特征

近年来，我们先后在青藏高原的古里雅冰帽、唐古拉冰川和希夏邦马地区钻。取了大量冰芯。在这些冰芯中保存着大量的环境变化信息。特别是反映沙暴、尘暴和浮尘等环境事件的尘埃冰志记录，是目前我们所能得到的记录最详细、分辨率最高和最连续的资料系列。青藏高原冰芯中尘埃指标显示，在气候变冷时，青藏高原的尘暴、沙暴和浮尘等事件出现的频率增多，强度增大；在气候变暖时，则尘暴、沙暴和浮尘等事件的频率减少，强度减小。目前，在青藏高原面上，正经历着气候变暖、环境改善的过程。

ENVIRONMENTAL RECORDS IN ICE CORES AND THEIR SPATIAL COUPLING FEATURES

Since 1984, a lot of ice cores have been drilled from the Dunde Ice Cap, the Tanggula glacier, the Xixiabama Ice Cap and the Guliya Ice Cap. These ice cores recorded past environmental events related to sandstorm, duststorm, and floating dust. The dust indices in ice cores from the Dunde and the Guliya Ice Caps both indicate that when it was becoming colder, the frenquency and intensity of duststorm, sandstorm and floating dust were increasing in the Tibetan Plateau, but when it was becoming warm,er, their frequency and intensity were decreasing. At present, the Tibetan Plateau is in the course of climatic warming and environmental amelioration. By comparing the dust record in ice cores from the Dunde Ice Cap located in the north margin of the Tibetan Plateau with the historical dust record in East China, it was found that a spatial identity of environmental changes existed not only in the Tibetan Plateau and its adjacent regions, but also in all parts of China where past environmental records is available. The latest achievement obtained in our ice core study is to first reveal that there has been a synchronous trend of variation between dust records in ice cores from the Tibetan Plateau and Greenland since the Little Ice Age. During the period of the 16th to the 18th century, both regions underwent the most considerable environmental changes in the past 500 years. Afterwards, both the frequency and the intensity of dust events decreased from the middle 18th century to the early 19th century, in turn increased from the middle 19th century on, and again decreased obviously after the middle 20th century. The results of correlation analysis between the dust records in ice cores from both regions show that the longer the time scale, the more remarkable the degree of correlation: the correlation coefficient is 0.3 on a scale of 10 years, 0.5 on a scale of 50 years, and 0.6 on a scale of 100 years. In order to understand the causes of spatial coupling of dust records in ice cores, it is necessary to firstly study why dust increases in ice cores. There are three factors which directly influence the variation of dust intensity: sources, removal intensity and transport intensity. Our study suggests that the high arid-cold region ofAsia centered by the Tibetan Plateau should be an important affecting source of the Northern Hemispheric environmental changes. The identity of the records in ice cores from Greenland and Guliya is only evidence from one aspect. The Asian monsoon system is a major driving force to couple environmentalchanges on a large spatial scale. Alternately varying |strengths of summer and win'ter monsoons control the intensity of environmental events. When summer monsoonis strong(winter monsoon is weak), the climate is warm, the precipitation increases and the environment ameliorates, resulting in the decrease of the transport amount and intensity of dust. This means that the dust amount carried to other regions o f the Northern Hemisphere will decrease, and so the dust concentration recorded .in ice cores from the Tibetan Plateau and Greenland will decrease. When summer monsoon is weak (winter monsoon is strong), the climate is cold, the precipitation decreases and the environment deteriorates, resulting in the increase of the transport amount of dust and then in the increase of dust deposited on the surfaces of the Tibetan Plateau Ice Caps and the Greenland Ice Sheet. The Tibetan Plateau plays a pivotal role not only in the monsoon driving system but also in the environmental coupling system. Firstly, the Tibetan Plateau it.self can trigger monsoon. Secondly, the surface condition of the plateau (especially 'differential snow cover and soil moisture) is a key factor to affect the strength of summer and winter monsoons. Moreover, as a major part of the arid-cold region in the Central Asia, the plateau is not only a major source to supply plenty of terrigenous materials but also the most effective position to carry such materials into the middle and upper troposphere because of its height.