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General circulation model simulation of the ¹⁸O content of continental precipitation in the middle Cretaceous: A model-proxy comparison

¹ Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA
² Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA

We use the GENESIS atmospheric general circulation model (GCM) with water isotopic transport and fractionation capabilities to quantify the influence of atmospheric CO₂, sea level, and elevation of the Western Cordillera on the ¹⁸O of middle Cretaceous precipitation. The model predicts a systematic increase of nearly 3 in the ¹⁸O of North American precipitation due to warming associated with an increase in CO₂ from 2 to 12 times pre-industrial levels. In contrast, the specification of lowstand conditions and a high ancestral Western Cordillera reduces the ¹⁸O of North American precipitation locally by as much as 6 and 8. We compare the simulated ¹⁸O of precipitation with the ¹⁸O of paleosol siderite spherules and find good agreement only when the model includes lowstand conditions and a high ancestral Western Cordillera. Our results imply either that Cretaceous high-latitude paleosol ¹⁸O was influenced by orographic precipitation and the Western Interior Seaway, or that the GCM's hydrological cycle is deficient at high pCO₂. Additional paleosol data are needed to resolve this issue.

Key Words: paleoclimate • Cretaceous • siderite • ¹⁸O • general circulation model

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