中国现代冰川平衡线分布特征与末次冰期平衡线下降值研究

Distribution and features of the glaciers' ELAs and the decrease of ELAs during the Last Glaciation in China

青藏高原及周边山地拥有地球上最高大且最广阔的高山高原，是除两极外最大的现代冰川作用中心，这也使得中国成为中低纬度地区现代冰川最发育的国家之一．现代冰川平衡线分布具有纬度地带性特征，在青藏高原上还呈不对称的环状．根据相关研究资料估算，中国末次冰期最盛期时的冰川面积约为50×10^4km^2，是现代的8．4倍．基于平衡线处年降水量和夏季平均气温（6-8月）之间的相关关系重建的中国西部（105°E以西）末次冰期最盛期时的平衡线分布图与现代的相似．在青藏高原内部与西北部，平衡线下降值在500m以内，小的仅为200～300m；在青藏高原东南边缘下降值约800m，最大可达1000～1200m．天山与阿尔泰山平衡线下降值均在500m左右．中国东部（105。E以东）没有发育现代冰川，仅有数处中高山地，如贺兰山、太白山、长白山与台湾山地保存有确切的末次冰期冰川地形，末次冰期最盛期时的平衡线下降800—900m，大于青藏高原、天山与阿尔泰山地区的下降值．根据中国东部末次冰期的平衡线分布图以及相关的古气候与古环境研究资料，海拔2000m以下的中低山地在第四纪期间任何一次冰川作用中都不具备冰川发育所需的地势条件．

The Qinghai-Xizang plateau and its bordering mountains is a special geographical unit in the low and middle latitudes in the Northern Hemisphere, it has widest plateau and many peaks higher than 8 000 m a. s. 1. This special geographical unit is a large center of modern glaciation, behind the polar regions （ the Antarctica and the Greenland）, making China to be a largest glacier country in the low and middle latitudes on our planet. The main feature of the modern equilibrium line altitude （ELA） is latitudinal zonality, increasing about 150 m per degree from 49 N to 28 N. Moreover, the ELA appears asymmetric rings on the plateau. Based on the published literatures, the glaciers during the Last Glacial Maximum were estimated to be 50 ×10^4 km^2, 8.4 times larger than that of modern glaciers. According to the relationship between summer （June to August） average tempera- ture and annual precipitation at ELA, the ELAs in western China （to the west of 105° E） during the LGM have been reconstructed, and the distribution and features of ELAs were similar to that of present. In the interior and the northwest of the plateau, the decrease of ELAs was less than 500 m, commonly, 200 to 300 m, whereas, the decrease of ELAs was about 800 m on the southeastern margin of the plateau, with a maximal decrease of about 1 000 to 1 200 m. The decrease of ELAs is about 500 m in the Tianshan and Altai ranges. However, there are no glaciers in eastern China （to the east of 105~ E） at present. The glacial landforms that formed during the last glacial cycle have been preserved in several mountains, such as Helan Mountains, Taibai Mountains, Changbai Mountains and high mountains in Taiwan Island. The decrease of ELAs was 800 to 900 m, with an absolute val- ue larger than that in western China. According to the reconstructed map of ELAs during last glaciation, and considering the palaeoclimate and paiaeoenvironment, it is very clear that there were no glaciers developed on the mountains with peaks less than 2000 m in eastern China during Quaternary.