40～30ka B.P.中国西北地区暖湿气候的地质记录及成因探讨

新疆艾丁湖与柴窝堡湖记录、玛纳斯湖记录、巴里坤湖记录、伊犁黄土-古土壤记录、罗布泊沉积记录和塔里木盆地南缘克里雅河流阶地钙质结核层记录,青海察尔汗盐湖以及内蒙古古居延海沉积记录、白碱湖和吉兰泰盐湖、巴丹吉林沙漠钙质胶结层等记录均显示40～30kaB.P.时期整个西北地区气候温暖湿润.其中,内蒙古西部温度较现代高2.～3℃,西北大部分地区降水量成倍增加,气候显著湿润化.其成因可能是由于当时中、低纬度岁差周期高辐射所造成的海洋表面温度升高,蒸发加强,西风环流和夏季风为西北提供的水汽大幅度增多的缘故.

WARM-HUMID CLIMATE IN NORTHWEST CHINA DURING THE PERIOD OF 40～30ka B. P. :GEOLOGICAL RECORDS AND ORIGIN

A large number of geological records from Northwest China, including ice core, lake sediment, pollen and loess-paleosol, were examined in this paper. During the period of 40～30ka B.P., the Aiding Lake had an area of 2 500～3 000km2. The Chaiwobu Lake was much larger than its present size and might be connected with the Aiding Lake. The Manas Lake, a dry saline lake today, experienced a humid episode in 37～32 14C ka B.P., with a lake area of 8 000 km2. The Balikun Lake was a deepwater one. The Lop Nur Lake was far wider than its present size, and its slight saltiness is supported by many hydrophyte pollen grains, expecially Typha . Calcareous crusts in the terrace of the Keriya River on the southern margin of Tarim Basin indicate that precipitation at that time should be 3～8 times higher than the present one. The Qarhan Lake was 2.6 times greater than the present size, with an annual precipitation of 150 to 350 mm. Between 41 and 33 ka B.P. the highest lake level of the Juyan Ze Lake was at 22 to 30 m above the present lake level. A lake of about 33 000km2 occurred in the Gashun/Aogun Nur area. A 50 cm-thick calcareous crust in Badain Jaran Desert indicates that precipitation should be 2～7 times than the present one. Between 40 and 23ka B.P. a lake occurred at Baijian Hu of Tengger Shamo. There was a relatively warm-humid climate in the Duantouliang region of northwestern Tengger Desert, where temperature was 2°～3℃ than the present one and precipitation was 250～350 mm more than the present one, developing a broad-leaf forest. The causes responsible for such changes were probably due to the increase in ocean surface temperature and evaporation resulted from high radiation caused by precessional at middle and low latitudes and therefore westerly circulation and summer monsoon carried large amount of moisture to Northwest China.