古大氣二氧化碳變化趨勢與白堊紀溫室氣候

王永棟

摘 要：白堊紀由于具有“溫室氣候”以及若干重大地質事件，使得其成為地質歷史上最引人注目的時期之一。利用替代指標重建大氣二氧化碳濃度對于理解白堊紀“溫室”氣候至關重要。在該文中，我們總結了基于古植物或地球化學數據重建二氧化碳濃度的主要方法，并綜合分析白堊紀期間的二氧化碳濃度變化。結果表明，在整個白堊紀時期大氣二氧化碳水平相對較高，但在白堊紀早期較低，白堊紀中期達到最高，而白堊紀晚期逐漸降低。然而，這個總的趨勢被大洋缺氧事件（OAE）和白堊紀末期地質事件相關的幾次快速變化打破。從古植物、古土壤學方面獲得的古CO2濃度新數據不僅支持了地球化學模型指示的整體趨勢，還提供了更精確的氣候快速變化引起的短期波動記錄。白堊紀中期漫長的靜磁帶有限的時間分辨率制約了我們更全面了解二氧化碳—氣候地對應關系。但是在含有可測年齡的火山巖地層剖面中，可以獲得新的古二氧化碳濃度及氣候數據，這將讓使得我們更好地理解大氣二氧化碳波動、氣候變化和地質事件之間的關系。

關鍵詞：大氣二氧化碳 白堊紀 氣孔指數 古土壤 地球化學模型 溫室氣候

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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