We investigate the effect of changes in the tectonic boundary conditions on global ocean circulation patterns. Using a fully coupled climate model in an idealized setup, we compare situations corresponding to the late Oligocene, the early Miocene, and present day. The model results show the existence of a flow reversal through the Panama Seaway between the Oligocene and Miocene. This flow reversal is induced by global tectonic changes related to the widening of the Southern Ocean passages and the closing of the Tethys Seaway. It mainly involves the wind-driven ocean circulation, in agreement with previous model studies. The global thermohaline circulation in the Oligocene and Miocene simulations is significantly different from the present-day conveyor circulation, as there is deepwater formation in both the North Atlantic and the North Pacific oceans. In particular, in the Oligocene simulation the salinity contrast between the Atlantic and Pacific oceans is reduced because of water mass exchange through the low-latitude connections between the two oceans.