The mid-Cretaceous was a period of unusually active tectonism that drove enhanced volcanic outgassing and high seafloor spreading rates. This intense tectonic activity is coincident with dramatic events in the marine environment, including oceanic anoxic events 1 (Aptian-Early Albian) and 2 (Cenomanian/Turonian boundary), high biological turnover rates, and a thermal maximum. In this study, a series of mid-Cretaceous ocean general circulation model experiments were completed using the Parallel Ocean Climate Model. These experiments demonstrate the effect of enhanced atmospheric CO2 concentrations and paleogeographic change on the global oceanic circulation. The experiments reveal that paleogeography, specifically the presence/absence of a marine connection between the North Atlantic and South Atlantic basins, may have governed the nature of the mid-Cretaceous global oceanic circulation. In the absence of this connection, an Albian simulation is characterized by extremely warm, saline conditions throughout the North Atlantic and northern South Atlantic Oceans. With a gateway in a Turonian simulation, Antarctic Bottom Water ventilates the Atlantic basins. In both Albian and Turonian simulations the Pacific-Indian basins are dominated by thermohaline circulation with deep water sources in the Southern Ocean. While atmospheric CO2 concentrations influence the global temperature and salinity, an increase from present-day to 4 times present-day levels alters the global circulation very little. Differences between the Albian and Turonian numerical simulations agree well with aspects of the marine record, supporting speculation that the climatic and oceanographic changes surrounding the Cenomanian-Turonian boundary were driven by the initiation of a connection between the Atlantic Oceans. ¿ 2001 American Geophysical Union