FOR 1070: Understanding Cenozoic Climate Cooling: The Role of the Hydrological Cycle, the Carbon Cycle and Vegetation Changes

自白垩纪末期以来，地球的气候一直在不断变化，大约在6550万年前。白垩纪的特点是极端温暖的“温室气候”，极地无冰，海平面上升，而持续到今天的普遍降温趋势始于随后的新生代。深海沉积物中的证据表明，这种气候发展并不总是连续的。在始新世到渐新世（约3400万年前）以及中新世中期（约1400万年前）的过渡时期，都发生了较大的降温事件，每次都伴随着南极冰川作用。降温事件可能是由海洋环流的全球变化引起的，而海洋环流的变化可能受到海洋门户构造变化的影响。另一种假说试图用大气二氧化碳（CO2）含量的变化来解释新生代的气候变化，二氧化碳含量的减少可能是由于大陆风化作用加剧和/或陆架海有机沉积物沉积增加，最终导致南极冰川作用和全球变冷。该研究股处理上述概述的新生代气候发展，并审查水和碳循环和植被的作用以及非二氧化碳温室气体的作用。首先，研究的重点是中新世中期的变冷和随后的草原扩张以及现代全球海洋环流的演变。另一个主题是始新世到渐新世过渡期间的冷却。系统地，检查包括基于数据的古环境重建以及数值模型研究。特别强调了用陆地和海洋沉积物数据测量模型结果。

Since the end of the Cretaceous about 65,5 million years ago the Earth's climate has been constantly changing. While the Cretaceous was characterised by an extremely warm "greenhouse climate" with ice-free polar regions and an increased sea level, a general cooling trend that persists until today started in the subsequent Cenozoic. Evidence in deep-sea sediments indicates that this climatic development has not always been continuous. Larger cooling events took place during the transition from the Eocene to the Oligocene (about 34 million years ago) as well as during the mid-Miocene (about 14 million years ago), each time accompanied by Antarctic glaciation. The cooling events were possibly caused by global changes in ocean circulation, which might have been influenced by tectonic shifts in ocean gateways. Alternative hypotheses try to explain Cenozoic climate changes with variations of the atmospheric carbon dioxide (CO2) content, which might have decreased because of a higher continental weathering and/or the increased deposit of organic sediments in shelf seas, finally leading to Antarctic glaciation and global cooling. The Research Unit deals with the above outlined climatic development in the Cenozoic and examines the role of water and carbon cycles and vegetation as well as the role of non-CO2 greenhouse gases. First, research focusses on the mid-Miocene cooling and the subsequent expansion of grassland as well as the evolution of the modern global ocean circulation. Another subject-matter is the cooling during the transition from the Eocene to the Oligocene. Methodically, the examinations include data-based reconstructions of the palaeoenvironment as well as numerical model studies. Special emphasis is put on surveying the model results by terrestrial and marine sediment data.