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对北京大学未名湖底泥层做了2 10 Pb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 174 7— 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 174 7年以来的气候变化 :186 6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 190 7— 192 6年是近 2 50年以来气候最为温暖湿润的时期 ;介于两者之间的 186 7— 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。
Peking University unnamed lake sediments done 2 10 Pb dating and 137 Cs time-marking and dating of oxygen and carbon isotopes. The results show that the sediment layer of about 50 cm in thickness was formed between AD 174 and 1997. The oxygen and carbon isotopic composition and organic content of carbonate in the lake mud record the climate change since 1774 in the Beijing area: In the past, the prevalence of the winter monsoon was relatively cold and dry. After 1887, the summer monsoon prevailed and the climate was warm and humid with 190 to 192 years being the warmest and humid climate in the past 250 years. Between 186 1886 is a time of rapid climate change and a period of frequent natural disasters.