北京大学未名湖沉积物中公元1747年以来气候变化的氧碳同位素记录

The Records of δ^(18)O and δ^(13)C for Climate Changes in Weiminghu Lake,Peking University since 1747a? A.D.

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。

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) 50～26?cm (1747\|1866a A.D.),which gave higher value of oxygen and lower value of carbon isotope.The δ 18 O value of samples ranges from -4.70‰ to -6.03‰,the δ 13 C value ranges from -3 63‰ to -6.03‰.\;b) 26～22?cm (1867\|1886a A.D.),which is characterized by a rapid change of value of oxygen and of carbon isotope.The δ 18 O value have a rapid downfall from -5.23‰ to -7.58‰,and the δ 13 C value have a rapid uplift from -5.70‰ to -2.18‰.\;c) 20～0?cm (1886\|1997a A.D.),which gave lower value of oxygen and higher value of carbon isotope.The δ 18 O value of samples ranges from -7.02‰ to -8.08‰,the δ 13 C value ranges from -2 03‰ to -2.63‰.\;Generally,the values of δ 18 O in lacustrine sediment has a positive correlation with that of the δ 18 O 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 δ 13 C 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 ( δ 18 O and δ 13 C) 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..