Late cretaceous ocean circulation in the south Atlantic and Pacific oceans

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Cooling during the last 15 million years of the Cretaceous is widely believed to have resulted in a reorganization of ocean circulation, with cooler periods being associated with deep ocean convection in high latitude regions (e.g., Robinson et al., 2010; MacLeod et al., 2011; Robinson and Vance, 2012; Jung et al., 2013). Understanding the relationship between climate change and sub-surface ocean circulation patterns, and gaining further insight into how circulation dynamics were influenced by the unique Cretaceous paleobathymetry is crucial to furthering our understanding of global climate dynamics during the Late Cretaceous. To provide further insight into Late Cretaceous ocean circulation we used neodymium isotopes as a tool to infer past ocean circulation patterns. Neodymium was extracted from fossilized fish teeth and bone fragments from bulk rock samples at 26 different sites (4 Pacific, 12 South Atlantic, 3 North Atlantic, 3 proto-Indian Ocean). We present two regional studies that focus on Campanian (84-72 Ma) and Maastrichtian (72-66 Ma) circulation patterns in the Pacific (Chapter 2) and South Atlantic (Chapter 3) Oceans. These chapters argue that, by the end of the Cretaceous, climate had cooled enough to support high latitude convection but also that circulation patterns were tightly controlled by bathymetry. To investigate the global implications of these two regional studies we also present preliminary neodymium isotopic data from several sites in the North Atlantic and proto-Indian Ocean (Chapter 4). Further, neodymium isotopic trends were compared to climate model simulations as well as to previously published neodymium, carbon, and oxygen isotopic records.