古大气二氧化碳变化趋势与白垩纪温室气候

王永栋

摘 要：白垩纪由于具有“温室气候”以及若干重大地质事件，使得其成为地质历史上最引人注目的时期之一。利用替代指标重建大气二氧化碳浓度对于理解白垩纪“温室”气候至关重要。在该文中，我们总结了基于古植物或地球化学数据重建二氧化碳浓度的主要方法，并综合分析白垩纪期间的二氧化碳浓度变化。结果表明，在整个白垩纪时期大气二氧化碳水平相对较高，但在白垩纪早期较低，白垩纪中期达到最高，而白垩纪晚期逐渐降低。然而，这个总的趋势被大洋缺氧事件（OAE）和白垩纪末期地质事件相关的几次快速变化打破。从古植物、古土壤学方面获得的古CO2浓度新数据不仅支持了地球化学模型指示的整体趋势，还提供了更精确的气候快速变化引起的短期波动记录。白垩纪中期漫长的静磁带有限的时间分辨率制约了我们更全面了解二氧化碳—气候地对应关系。但是在含有可测年龄的火山岩地层剖面中，可以获得新的古二氧化碳浓度及气候数据，这将让使得我们更好地理解大气二氧化碳波动、气候变化和地质事件之间的关系。

关键词：大气二氧化碳 白垩纪 气孔指数 古土壤 地球化学模型 温室气候

Palaeo-CO2 Variation Trend and the Cretaceous Greenhouse Climate

Wang Yongdong

（Nanjing Institute of Geology and Palaeonotology，Chinese Academy of Sciences）

Abstract：The Cretaceous was one of the most remarkable periods in the geological history， with a “greenhouse” climate and several important geological events. Reconstructions of atmospheric CO2 using proxies are crucial for understanding the Cretaceous “greenhouse.” In this paper we summarize the major approaches for reconstructing CO2 based on palaeobotanical or geochemical data， and synthesize the CO2 variations throughout the Cretaceous. The results show that atmospheric CO2 levels remained relatively high throughout the Cretaceous， but were lower in the early Cretaceous， highest in the mid-Cretaceous and gradually declined during the late Cretaceous. However， this overall trend was interrupted by several rapid changes associated with ocean anoxic events （OAEs） and the end-Cretaceous event. New data on paleo-CO2 levels from palaeobotanical and palaeosol evidence support not only the overall trends indicated by geochemical models， but provide more precise records of the short-term fluctuations related to brief episodes of climate change. Temporal resolution within the long quiet magnetic period in the middle Cretaceous is one of obstacles preventing us from a more comprehensive understanding of the CO2 climate linkage. But new palaeo-CO2 determinations and climatic data from stratigraphic sections of sediments intercalated with datable volcanic rocks will allow a better understanding of the relationships between fluctuations of atmospheric CO2， climate change， and geological events.

Key Words：Atmospheric CO2； Cretaceous；Stomata index； Palaeosol； Geochemical model； Greenhouse climate

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