Evolution of Glaciers and Environment in the West Kunlun Mountains During the Past 32 ka
JIAO Ke-qin, YAO Tan-dong, LI Shi-jie (Cold and Arid Regions Environmental and Engineering Research Institute, CAS, Lanzhou Gansu 730000 China) (Nanjing Institute of Geography and Limnology, CAS, Nanjing Jiangsu 210008. China)
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.