乌鲁木齐河下游地区30KaBP以来湖泊沉积的孢粉组合与古植被古气候

POLLEN COMPONENT OF LACUSTRAIN DEPOSIT AND ITS PALAEO-ENVIRONMENT SIGNIFICANCE IN THE DOWNSTREAM REGION OF URUMQI REVER SIENCE 30Ka BP

根据乌鲁木齐河尾闾东道海子沉积的孢粉分析 ,以藜科、蒿属花粉的绝对含量和相对比值确定古植被类型 ,重建下游平原 30KaBP以来的古气候演变过程。表明末次冰期北疆山麓地带的相对冷湿环境 ,在本区孢粉组合中也有一定显示 ;全新世大暖期山前平原地区湖泊来水量增加 ,湖泊周边湿地沼泽遍布 ;最近 5 0 0年来的植被变化与区域气候环境的干暖化趋势有关 ;而近 10 0年来的植被退化、环境劣变主要是人类自身行为所致。

Urumqi River lies in the north foot of Tianshan Mountain and south brink of Gurbantunggut Desert in Xinjiang, which is 200 kilometres long and covers an area of about 10 000 square kilometers. The modern climate of the river basin is the continental climate of the north temperate zone in the center of Asia, which is less rainfall and more evaporation. Dongdaohaizi Lake lies in the terminal of Urumqi River, which is also located between the longitudinal dunes in the Desert. The water of the lake comes from the upper reaches, which originates from rainfall, snow and glacier over the Tianshan Mountain. The modern vegetation around the lake is desert steppe. The sample core drilled through 10 meters below the lakebed. Forty lacustrain deposit samples were collected from the core with 25cm interval. On the basis of pollen component analysis of the samples, this paper rebuilds the paleo-climate variation series of the downstream plain of Urumqi River since 30Ka BP. Some conclusions are as following: (1) Totally more than 5 000 grains of pollens have been determined, of which, desert herbs or bush pollen occupied a dominant position , and the spore-pollen sequence can be divided into five zones ; (2) It is found that the increase of the Chenopdiaceae, Artemisia and Ephedraceae in ZoneⅠ,ⅣandⅤ reflected the dry tendency about the climate and increase of the Typha, Phragmites communty and Picea in Zone Ⅱand Ⅲ reflected the wet tendency in this area. (3) It is characteristic that the desert vegetation and dry tendency became more dominant since 30Ka BP, and the prevailing climate was fairly dry of desert steppe or desert type over this area, which resulted from the geographic location of the area and the background of Global changes ; (4) The relatively wet and cold climatic environment during the Last Glaciation shown not only in the foot of mountains in Northern Xinjiang, as well as in the pollen component of the lacustrain deposit in this area, such as ZoneⅡshowing, which may be influenced by the climate system of strengthened westlies; (5) During the Magthamal in Holocene, the water of the lake increased obviously and the wetland around the lake spreaded extensively, which may be influenced by the that of strengthened East Asia Monsoon; (6) Since 500a BP the vegetation and climate over the area varied with the obvious dry tendency regionally, accompanied with small cold and warm of climate variation series, which may be influenced by that of the Little Ice Age; (7) Since 100a BP, the degeneration of the biological diversity and ecological environment in the area were resulted from the human activity, such as building reservoirs, cutting desert bushes and so on. Thus, it is very important to protect ecological environment during the exploiting West China.