相关基金:Supported by Key Technologies R&D Program from Ministry of Science and Technology of the People s Republic of China (2007BAD46B08); Program for Fostering Special Talents of Glaciology and Cryopedology of the National Basic Sciences Talents Fundation(J0630966); Key Technologies R&D Program of Gansu Province(090NKCA075); Natural Science Fundation of Gansu Province (3ZS041-A25-002)