西昆仑山32ka来的冰川与环境演变

Evolution of Glaciers and Environment in the West Kunlun Mountains During the Past 32 ka

通过野外考察、实验室样品分析和年代测定，综合讨论了西昆仑山３２ ｋａ以来几个特征时段的 冰川与气候环境变化．末次冰期冰盛期，气温比现代低９℃，降水量不足２００ｍｍ．冰川规模比现代 大 ２．２倍，平衡线降低值在 ３００～４００ ｍ．新仙女本期．除气温急剧降低外，并伴随着大气尘埃含量 的迅速增加全新世早期，气候波动非常之剧烈，并导致了降温事件和与之相伴随的冰进事件，但 这并没有改变升温的总趋势．全新世中期，最暖期时，温度高于现代１．５℃．并在末次冰期冰盛期的 冰碛上发育了土壤和古土壤．全新世晚期，新冰期开始于４０００ａＢＰ．可明显分为３次．小冰期的３ 次冷期发生在１５， １７和１９世纪。

There are 5 485 glaciers in the West Kunlun Mountain now, with an area of 8 817.78 km2, more than 3 / 4 of the total area in the whole of Kunlun Mountains. In the West Kunlun Mountain glaciers are concentrated and large in scale. There is Guliya Ice Cap, 376.05 km2 in area, the largest ice cap found in the regions of low and middle latitudes in the world up to now. Observations show that in the Tibetan Plateau air and ice temperatures are lowest around the ice cap. For example, the lowest air temperature at 6 000 m a.s.1. over the ice cap is -60.5 ℃, and the ice temperature is -18.6℃ at the depth of 10 m, and -2.0 ℃ at the bottom. respectively. Annual precipitation is only about 300 mm. All these show that the glaciers are extra-continental or polar type. In this paper the evolution of glaciers arid environment in the West Kunlun Mountains in several typical periods during the past 32 ka are discussed based on the field investigations during 1985- 1987 and 1990- 1992 and on the 14C dating. According to the Guliya ice core records, the extremely low temperature occurred in 23 ka BP. in accordance with the Last Glaciation Maximum. 32- 15 ka BP. Furthermore, the air temperature at that time was 9 ℃ lower than that at present; the annual precipitation was less than 200 mm, whereas the scale of the glaciers was 2.2 times larger and the snow line was 300-400 m lower than that at present, respectively. A glacial advance in the Younger Dryas Event was firstly revealed by the records in the Guliya Ice Cap, which occurred in 10 990 ?190 a BP and 10 553 ?123 a BP respectively according to 14C dating, that is in accordance with those reported in both the docords reveal the Younger Dryas Event occurring during the period of 12.2-10.8 ka BP, when air temperature dropped to the lowest point in 11.05 ka BP, δ18O reduced to -21 .8%, and atmospheric dust content reached the highest value. The ice core records reveal that the climate fluctuated violently in the early Holocene when temperature increased, especially during the last 500 years, resulting in a temperature-dropping event (9.0- 8.0 ka BP), together with glacial advances from 8 287 ?160 a BP to 8 134 ?176 a BP according to 14C dating. During the mid-Holocene. most glaciers on the northern slopes of the Karatax Mountains. adjacent to the Tarim Basin. disappeared, cirques were ice-free. and some soils and paleasols developed on the till during the periods from 7 078 ?340 a BP to 4 603 ?111 a BP according to 14C datings. However, the glaciers with polar features near the highest peak of the West Kunlun Mountains dwindled little at that time. During the late Holocene, global climate came into a new stage. i.e. Neoglaciation. started from 4 000 a BP in the West Kunlun Mountains and can be divided into three obvious sub-stages, i.e. the periods of3 983 ?120 a BP. 3 522 ?1 17 a BP and 2 720 ?85 a BP, respectively. During the Little Ice Age glaciers fluctuated frequently. Now the glaciers in West China are characterized by 2-3 end moraines. It is traditionally considered that the climatic fluctuations occurred in the 16th to 19th centuries during the Little Ice Age. The Guliya ice core records show there were three cold ages in the 15th, 17th. and 19th centuries respectively, the intensity of the third cold age was severer than those of the others.