XIAO Cun-de, QIN Da-he, REN Jia-wen, LI Zhong-qin, WANG Xiao-xiang
Large-scaled investigation of glaciochemistry in surface snow/ice may not only provide some information on global atmospheric processes, but also lay a solid foundation for rational interpretation of regional differences of palaeo-records in ice cores. Three key regions of the cryosphere, i.e., the Polar Regions as well as High Asia, are selected in this study for contrast study of impurities in surface snow/ice. The studied impurities include: 1) Major ions, such as Na+, Ca2+, Mg2+, Cl-, SO42- and NO32-, 2) Halogen element Br, 3) MSA and SO42-. The sources, seasonality, spatial distribution and their environmental implications are presented. Also, the contribution percentage of various sources to some elements is estimated. Large-scaled glaciochemical investigation reveals some information on global atmospheric processes. The major results can be summarized as follows: Marine aerosol is the major contributor to the glaciochemistry in Antarctic Ice Sheet. The impurities in surface snow at High Arctic may be a mixture of crustal, oceanic and anthropogenic origins. Spatial differentiation of glaciochemistry in Arctic is more complicated than those in Antarctica and High Asia. Compared with Greenland and north Canada, the Central Arctic Ocean is more influenced by the mid-latitudinal air mass, especially in winter and early spring. Ions emitted from open waters (such as shear zones) result in concentration peaks in snow over pack ice of the central Arctic Ocean. In High Asia, continental and regional dusts play an important role in glaciochemical records, but in south margin of the Tibetan Plateau, sea salt contents increase. There are two major atmospheric processes that control the features of glaciochemistry in High Asia, i.e., dust storms in north and monsoon in south of the plateau, and the two processes reach equilibrium around the Tanggula Range. In High Asia the windy season coincides with dry season, and the calm season coincides with precipitation season, which largely determines the seasonal transition of deposition functions (i.e., dry and wet deposition) of impurities into snow. The prevailing sources of the impurities in Central Arctic Ocean are mainly from Eurasia and Northwest America. The concentrations of impurities in surface snow on the Tibetan Plateau are higher in its northern and southern margins than those in the central plateau. Generally, the impurities recorded in surface snow on Antarctica may represent the global background, while those on Arctic may represent the background of the lower to middle troposphere in the north hemisphere, and those on High Asia may represent that of the middle to upper troposphere of the mid-latitudes. Large-scaled investigation of glaciochemistry may reveal some important aspects of global atmospheric processes, rational interpretation of ice records should base on more precise study on the sources, transportation and the air/ice interface processes of impurities.