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

自约655万年前白垩纪末期以来，地球气候一直在不断变化。尽管白垩纪的特点是极温暖的“温室气候”，极地无冰，海平面上升，但持续到今天的总体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持续的。在始新世向渐新世(约3400万年前)和中新世中期(约1400万年前)的过渡期间发生了更大的冷却事件，每次都伴随着南极冰川。冷却事件可能是由海洋环流的全球变化引起的，这可能受到海洋门户的构造变化的影响。另一种假设试图解释新生代气候变化随着大气二氧化碳(CO2)含量的变化而变化，大气二氧化碳含量可能已经减少，这可能是因为大陆风化程度更高和/或陆架海有机沉积物沉积增加，最终导致南极冰川和全球变冷。研究股处理上述新生代气候发展，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，重点研究了中新世中期的降温和随后的草原扩张以及现代全球海洋环流的演化。另一个主题是始新世向渐新世过渡过程中的冷却问题。从方法上讲，这些检查包括基于数据的古环境重建和数值模型研究。重点介绍了利用陆地和海洋沉积物资料对模型结果进行检验。

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.