黄土沉积物中△C的碳同位素组成与古大气二氧化碳浓度估算

The Carbon Isotopic Composition of △C in Loess Sedimentsand the Estimating of CO_2 Concentration in Paleo-atmosphere

本文提出了利用黄土沉积物中△Ｃ的碳同位素组成估算古大气二氧化碳浓度的方法。初步的估算结果表明，利用干旱、半干旱、温度低、强蒸发及植被不发育条件下形成的地表沉积物中△Ｃ的碳同位素组成定量地估算古大气二氧化碳浓度的方法是可行的，估算结果与冰岩芯气泡组分分析结果可进行较好的对比。大气二氧化碳浓度的变化与全球性的气候波动具有同步性。

It has long been known that CO, content of the atmosphere influences temperature by determining the amount of long-wave radiation trapped in the atmosphere. Therefore, Understanding the variation of atmospheric CO2 during Quaternary is very important for studying the influence of atmospheric CO2on global climatic change. UP till now the information on variation of atmospheric CO2 during Quaternary is mainly obtained by the composition analysis of ice core.Because the longeSt cores so far obtained (1400-3000m) cover only the last 100000-160000 years, the studying on variation, of atmospheric CO, during Quaternary is restricted.△C is a secondary carbonate in loess sediment with a characteristic thermo-decompositon interval(500600℃). The isotopic composition characteristics and geographical distributive feature of △C suggest that AC was formed under the condition of arid or semiarid, low temperatory, high evaporation and little vegetation. Under the condition loess CO2 is mainly from atmosphere and its carbon isotopic composition is veryclose to that of atmospheric CO2.The relationship between CO2 content of the atmosphere and its carbon isotopic composition in northwest of China is δl3C=5756/[CO2]-22. 7Replacing 813C of atmospheric CO, with that of △C, we preliminaryly estimate the CO2 content of the paleo-atmosphere. The results show that the CO2 content of the atmosphere from E1-1 to S3 ranges from 311. 1 × 10-6 to 397. 0× 10-6 and the difference between estimated values and measured values decreases with the climatic evolution from wet-warm to dry-cold.