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. Understanding of the role of ocean circulation on climate during the LateCretaceous is contingent on the ability to reconstruct its modes andevolution. Geochemical proxies used to infer modes of past circulationprovide conflicting interpretations for the reorganization of the oceancirculation through the Late Cretaceous. Here, we present climate modelsimulations of the Cenomanian (100.5–93.9 Ma) and Maastrichtian (72.1–66.1 Ma) stages of the Cretaceous with the CCSM4 earth system model. Wefocus on intermediate (500–1500 m) and deep (> 1500 m) oceancirculation and show that while there is continuous deep-water productionin the southwestern Pacific, major circulation changes occur between theCenomanian and Maastrichtian. Opening of the Atlantic and Southern Ocean, inparticular, drives a transition from a mostly zonal circulation to enhancedmeridional exchange. Using additional experiments to test the effect ofdeepening of major ocean gateways in the Maastrichtian, we demonstrate thatthe geometry of these gateways likely had a considerable impact on oceancirculation. We further compare simulated circulation results withcompilations of eNd records and show that simulatedchanges in Late Cretaceous ocean circulation are reasonably consistent withproxy-based inferences. In our simulations, consistency with the geologichistory of major ocean gateways and absence of shift in areas of deep-waterformation suggest that Late Cretaceous trends in eNd values in the Atlantic and southern Indian oceans were caused by thesubsidence of volcanic provinces and opening of the Atlantic and Southernoceans rather than changes in deep-water formation areas and/or reversal ofdeep-water fluxes. However, the complexity in interpreting Late Cretaceous eNd values underscores the need for new records as well asspecific eNd modeling to better discriminate between thevarious plausible theories of ocean circulation change during this period.

Paleogeographic controls on the evolution of Late Cretaceous ocean circulation