长白山现代理论雪线和古雪线高度

PRESENT AND LATE PLEISTOCENE EQUILIBRIUM LINE ALTITUDES IN CHANGBAI SHAN,NORTHEAST CHINA

根据冰川地貌和地形特征、岩性、冰川沉积物的风化程度以及OSL测年结果,认为长白山地区发育两期冰川作用,即末次冰盛期和晚冰期,测年结果分别为20.0±2.1ka和11.3±1.2ka。根据平衡线（ELA）处6~8月多年平均气温（T）和年降水量（P）的关系,计算长白山现代理论雪线高度为3380±100m。通过积累区面积比率AAR（accumulation-arearatio）、冰川末端到山顶高度TSAM（the terminal to summit altitudinal）,冰川末端至分水岭平均高度Hofer（the terminal to average elevation of the catchment area）、末端至冰斗后壁比率THAR（toe-to headwall altitude ratios）、冰斗底部高程CF（cirque-floor altitudes method）、侧碛堤最大高度法MELM（maximum elevation of lateral moraines）等方法计算该区末次冰盛期雪线高度为2250~2383m,平均值2320±20m。考虑到末次冰盛期后地壳上升20m,当时雪线的实际高度为2300±20m,冰盛期的雪线降低值为1080±100m。晚冰期北坡和西坡的雪线高度分别为2490m和2440m,平均值2465m,考虑新构造运动后的雪线实际高度2454m,降低值926±100m。长白山新构造运动（LGM上升约20m,晚冰期上升约11m）在末次冰盛期以来对冰川发育的影响不明显。

Changbai Shah,41°58′ -42°06′N in latitude and 127°54′- 128°08′E in longitude,is situated in the eastern margin of the Eurasian Plate and on the West Pacific rim. It is the highest area in the mainland of Northeastern China, reaching an altitude of 2691m a. s. 1. at the peak of Baiyun. The reconstruction of palaeo-climatic changes is based on the equilibrium line altitudes （ELA） of former glaciers. According to the glacial landforms and deposits with the optically stimulated luminescence （OSL） dating resuhs, two glacial stages, the Last Glacial Maximum （LGM） and the Late-Glacial were identified. The Late Glacial stage （Meteorological Station glacier advance）took place at about 11 ka （ 11.3± 1.2ka） before, and the LGM, named Black Wind Mouth glacier advance, occurred at 20ka（20.0 ± 2. 1 ka）before. Based on the Ohmura＇s formula of the relationship between summer（JJA）atmospheric temperature（T） and the annual precipitation（P） at ELA, the present theoretical equilibrium line altitude（ ELA, ） in Changbai Shan should be 3380 ± 100m. Six methods of accumulation-area ratio （AAR）, maximum elevation of lateral moraines （ MELM ）, toe-to headwall altitude ratios （ THAR ）, the terminal to summit altitudinal （ TSAM）, the altitude of cirque floor（CF） , and the terminal to average elevation of the catchment area（Hofer） were used for calculation of the former ELAs in different stages. These methods provided the ELA for a range of 2250 - 2383m with an average value of 2320 ± 20m during the LGM, which is 200m higher than previous investigation. The snowlines during the Late Glacial are 2490m in northern slope,and 2440m in western slope. The results show that the snowline in northern slope is 50m higher than that in western slope during the Late Glacial, and the average snowline value is 2465m. The ELA was not only affected by ancient temperature and precipitation,but also affected by neo-tectonic uplift factor. Adopted 1 mm/a as the uplift value,the real snowline is calculated to be 2300 ± 20m during the LGM, and 2454m during the Late Glacial. The AELA values were more than 1000m（ 1080± 100m） higher during the LGM and about 920m （926 ± 20m） lower during the Late Glacial respectively than that of the present. Compared with Taiwan and Japanese mountains in East Asia during the LGM,the effect of the ELA in Changbai Shan during the glaciations （i. e. 20m uplift in the LGM and 11m in the Late Glaci uplift on al） is not obvious. The ELA values provide a potentially powerful method of quantifying palaeoclimates in Changbai Shan where other forms of evidence are lacking during the last glacial cycle. These calculated modern theoretical equilibrium line and former ELAs in different glacial stages would be helpful to correctly recognize the palaeoclimatic environment in the mountains of East Asia.