Abstract: According to the variation of stable isotopic composition of carbonate in lacustrine deposite in Weiminghu Lake, Peking University, the section can be subdivided into four oxygen-carbon-isotope stages. They are as follows: a) 50～26cm (1747-1866a A.D.), which gave higher value of oxygen and lower value of carbon isotope. The δ¹⁸O value of samples ranges from -4.70‰ to -6.03‰, the δ¹³C value ranges from -3.63‰ to -6.03‰. b) 26～22cm (1867-1886a A.D.), which is characterized by a rapid change of value of oxygen and of carbon isotope. The δ¹⁸O value have a rapid downfall from -5.23‰ to -7.58‰, and the δ¹³C value have a rapid uplift from -5.70‰ to -2.18‰. c) 20～0cm (1886-1997a A.D.), which gave lower value of oxygen and higher value of carbon isotope. The δ¹⁸O value of samples ranges from -7.02‰ to -8.08‰, the δ¹³C value ranges from -2.03‰ to -2.63‰. Generally, the values of δ¹⁸O in lacustrine sediment has a positive correlation with that of the δ¹⁸O values of rainwater in the Asian monsoon region, and the latter are controlled by monsoon climate. The summer monsoon have a lower value of oxygen isotope, and the winder monsoon have a higher value of oxygen isotope. The values of δ¹³C of carbonate in lacustrine sediment are controlled by that of the algae activity in the lake water and the latter has a positive correlation with temperature and humidity. So the high value of oxygen and lower carbon isotope (δ¹⁸O and δ¹³C) in lacustrine sediment in Weiminghu lake represents a relatively cool and dry weather while the low value of oxygen and higher carbon isotope represents a rather hot and wet weather. The variation of oxygen and carbon isotopic value among the section indicates a cool-dry climate during 1747—1866a A.D., a hot-wet climate during 1886—1997a A.D., and a rapid change of climate from 1866 to 1886a A.D..

Key words: Weiminghu Lake, δ¹⁸O, δ¹³C, climate change

摘要： 对北京大学未名湖底泥层做了²¹⁰Pb计年法和¹³⁷Cs时标法定年以及氧碳同位素分析。结果表明厚度约50cm的底泥层形成于公元1747—1997年之间，湖泥中碳酸盐的氧碳同位素组成和有机物含量记录了北京地区公元1747年以来的气候变化：1866年以前冬季风盛行，气候比较寒冷干燥；1887年以后夏季风盛行，气候比较温暖湿润，其中1907—1926年是近250年以来气候最为温暖湿润的时期；介于两者之间的1867—1886年是气候急剧转型的时期，也是自然灾害频繁出现的时期。

关键词: 未名湖, δ¹⁸O, δ¹³C, 气候变化