地史时期古大气二氧化碳变化趋势与温室气候——以中生代白垩纪为例

Variation of paleo-CO2 and greenhouse climate in the geological history: A case study from the Cretaceous of the Mesozoic

中生代不仅是地球发展和生命演化的重要阶段,同时也是距离现代最近的典型温室气候期。其中,白垩纪被视为地球历史时期温室气候的最佳范例之一。通过古植物气孔参数、古土壤同位素以及地球化学模型等途径的研究,可以勾勒出白垩纪这一典型温室气候环境下古大气二氧化碳浓度变化的大致轮廓。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。更重要的是,借助于这些地质参数还更精确地识别出在白垩纪关键时期出现了几次显著的古大气二氧化碳的短期快速波动变化,表明白垩纪的温室气候状态并非之前所想象的那么稳定,而是发生了几次大规模快速气候扰动事件,并伴随着二氧化碳浓度的短期波动变化。这项研究质疑了整个白垩纪期间气候温度均匀分布且呈现单一稳定温室状态的观点。

Mesozoic era is a crucial stage for the Earth development and life evolution, and is particularly significant for bearing typical greenhouse climate that is the closest to today. Among them, the Cretaceous is considered as one of the best example of the greenhouse climate in Earth history. Recent progresses including fossil plant stomata parameters, paleosol isotope and geochemical model, made it possible to synthesize the CO2 variations throughout the Cretaceous. The results showed that atmospheric CO2 levels remained relatively high throughout the Cretaceous, but they 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 of paleo-CO2 associated with some geological events. It thus showed that the Cretaceous greenhouse climate condition is not as stable as we thought before, but instead with some short-term fluctuations related to the brief episodes of climate change.