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

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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.