The concept of a stable, westward flowing circumglobal current throughout the Cretaceous Tethys has become the subject of extensive debate. Results from a series of oceanic general circulation model experiments, using the NCAR Parallel Ocean Climate Model, are presented which oppose this concept and suggest a more complicated circulation pattern dominated by a clockwise gyre in the Mediterranean Tethys. Although a narrow westward flowing current is simulated hugging the southern margin of Tethys, ocean model experiments reveal the large sensitivity of this current to paleogeographic evolution. Small modifications to continental geometry, representing sea level change or tectonic plate movement during the Cretaceous, alter the direction and strength of the Tethyan circulation and, consequently, lead to regional changes in seawater properties (i.e., temperature and salinity). These oceanic general circulation model experiments indicate that geographic evolution is an important mechanism of climatic and environmental change. Since the Cretaceous experienced rapid tectonic changes these results imply large surface circulation variations in the Tethys Ocean, supporting the idea of a dynamic tropical oceanic environment. In fact, a simulation of sea-level rise during the mid-Cretaceous reproduces the fluctuations in seawater properties recorded by fauna in the Caribbean Sea. ¿ 1998 American Geophysical Union