The nature of water exchange between the Mediterranean and the Atlantic is examined for three time periods during the late Neogene in order to assess the impact of flow patterns between these basins on bottom water conditions in the oceans. The large volume of carbonates and evaporites deposited in the Mediterranean during the Messinian salinity crisis appears to have caused the open ocean to become more undersaturated in calcium carbonate, resulting in increased dissolution of deep-sea carbonates during the latest Miocene. During the earliest Pliocene, an estuarine-type of flow existed between the Atlantic and Mediterranean. Waters entered the Mediterranean at depth and flowed out at the surface. Benthic foraminiferal stable isotopic evidence from the North Atlantic indicates that North Atlantic Deep Water (NADW) was produced throughout the early Pliocene and that the absence of saline Mediterranean outflow did not have a significant effect on bottom water production. Eustatic lowering of sea level during the last glacial maximum (18,000 years B. P.) reduced water exchange between the Atlantic and the Mediterranean. As a result, salinities in the Mediterranean increased substantially, but it seems unlikely that diminished NADW production during the last glacial episode can be attributed to a reduction in Mediterranean outflow.