国家自然科学基金项目41206182,41406219;中国南北极环境综合调查与评价专项CHINARE04-04,04-01,01-04;National Natural Science Foundation of China, No.41206182, 41406219;Comprehensive Investigation and Evaluation of the North and South Poles Environmental, China, No.CHINARE04-04, 04-01, 01-04