Blöhdorn, Janine (2013) Klima und Ozeanzirkulation der Frühen Kreide im Kiel Climate Model. (PhD/ Doctoral thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 121 pp.

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Abstract

The Early Cretaceous (~ 110 Ma) was one of the warmest periods during the Phanerozoic. During this time, Earth received about 1% less solar radiation compared to the present value, while the atmospheric carbon dioxide concentration was in the range of 800-2000 ppm. Proxy data suggest global mean temperatures higher than 20°C, a reduced meridional surface temperature gradient, and an enhanced hydrological cycle. The Atlantic Ocean was yet to evolve and the Proto-Pacific and the Tethys Seaway in the low latitudes allowed a circum-tropical oceanic flow. Although continental configuration and radiative forcing were different from the modern, the Early Cretaceous climate has been widely used as an example for a potential future high-pCO2 world. Furthermore, geological information about Oceanic Anoxic Events (OAEs) raised the question of how the ocean circulation and the enhanced runoff from land might have supported the formation of OAEs. The climate and ocean circulation during the Early Cretaceous is presented as simulated by the Kiel Climate Model (KCM), a fully coupled atmosphere-ocean general circulation model. For the atmosphere the focus is set on the surface climatology, the hydrological cycle, and the atmospheric circulation patterns. The discussion of the ocean circulation includes the horizontal surface flow, meridional overturning circulation, and regions of formation of intermediate and/or deep waters. As a result the simulated Early Cretaceous climate shows a strong warming associated with an enhanced hydrological cycle. The horizontal circulation throughout the atmosphere shows a significant strengthening, whereas the general circulation is weaker than today. The Cretacous ocean is characterized by a very stable stratification and allows weak overturning with the formation of intermediate water in the high-latitude Pacific and subtropical Tethys. No significant deepwater formation is simulated. The Arctic basin did not allow convection and might have provided a favourable environment of anoxic conditions. In low latitudes strengthened tropical ans subtropical cells provide intensified shallow overturning rates and in the eastern tropical Pacific interannual variability shows similar statistical features than the present-day ENSO.

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