Mt. Tanggula locates in the middle of High Asia, which belongs to the transition zone from arid and semi-arid continental climate to warm and moist marine climate. At the same time, as the source of Changjiang River, the gap region of Mt.Tanggula also is the sensitive area of climate variation. In those areas, the fragile ecosyetem is facing the interference from artificial environment, and the situation of soil and water loss begins to exacerbation. Based on present state, the study of ice core in this area has special significance on understanding of atmospheric chemistry and moist source. Moreover, this study also can perform a forewarning function for the changes of climate and ecological environment at the source of Changjiang River, even the whole river basin. In this paper, the dating and analysis about 32.4m Tanggula ice core from Middle Tibetan Plateau have been completed, then the process and possible mechanisms about changes of climate and environment in Middle Tibetan Plateau, which are revealed by Tanggula ice core are investigated. And the following conclusions can be achieved:
After analyzing the experimental data and the meteorological record, a raising trend about glacial net accumulation recorded in Tanggula ice core since the half past 19 century is found. In especial, this trend is shown obviously after 1960s. But the net accumulation has a slight decrease since the previous years of 1990s. In the 150 years records about glacial net accumulation, the low accumulation periods are before 1860 A.D, 1880~1910 A.D and 1950~1965 A. D, respectively. A same tendency is present between the 50 years variations in net accumulation recorded by Tanggula ice core and precipitation recorded by Tuotuohe Station, which lies at the north of M.t Tanggula. This shows glacial net accumulation can reveal the history of atmospheric precipitation near the Tanggula glacier. Otherwise, concerned topography, temperature, precipitation intensity and other factors, maybe there are some differences in net accumulation and actual precipitation in history.
The characteristics of major ions in Tanggula ice core show Ca2+ and HCO3- are the primary cation and anion, respectively. They account for 73.4% of the total mass. Ion concentration has some differences between in Tanggula and in other areas in Tibetan Plateau. the order of magnitude of ion concentration shows the concentration in Tanggula near this in ice core from South Tibetan, at the same time, the ion composition presents the similar form between Tanggula glacier and glacier in North Tibetan. The statistical analysis ( correlation analysis and EOF analysis) indicates ion species in Tanggula ice core can be classified 3 species: dust source ions ( Mg2+, Ca2+ and HCO3- ), salt lake and mineral source ions (SO42-, Na+, K+, Cl- ), anthropogenic and biogenic source ions (NH4+, NO3-). These ions most likely form compound including: Ca(HCO3)2, Mg(HCO3)2, Na2SO4, NaCl, (NH4)2SO4 and NH4NO3.
Different source ions have different ion deposition modes. Land source ions show dry deposition mode. Remarkable dry deposition in Cl- and Na+ shows sea salt transport is rather weak and evaporation from salt lake maybe is the important source for Cl- and Na+. Wet deposition process in NO3- and NH4+ exceed obviously dry deposition process, and the two ion combines likely into NH4NO3 , then deposition with precipitation process. Compared with NH4+, NO3- has a weak wet deposition, which shows part of NO3- maybe exist in aerosol in form of nitrate (such as NaNO3).
The ions concentration record in Tanggula ice core for 150 years shows 19 century is a higher dust period and the intensity of dust over one time than 20 century, so this period is looked as the last cold stage in Little Ice Age. At the same time, this core has record a climatic shift in 1920s and a cold event in1960s~1970s. Ice core reveals dust began to increase in this area since 1970s, but this case is different from 19 century, which is the result of climatic effect. In fact , the increased dust is result from natural environment interfered by human activity, which leads to destructive ecological landscape in source region.
SO42- concentration recorded by Tanggula ice core reveals most of sulfate in this area come from dust transport and salt lake evaporation. But in recent 50 years human activity lead to a increase in SO42- concentration. That means anthropogenic influence on atmospheric environment has extended to inner land of Tibetan Plateau. Both concentration of NH4+ and that of NO3- are showed to have a remarkable correlation with north-hemisphere air temperature. In recently decades, a higher concentration for NO3- and NH4+, respectively, indicates a temperature effect. At the same time, expansion of farmland and increased grassland in short term maybe is a important factor for increased NH4+ and NO3-.