A general circulation model is used to evaluate the impact of geographic differences between the early Eocene and the present day on ocean thermal structure. The model includes reconstructed Eocene bathymetry and surface thermal boundary conditions that mimic a diffusive atmosphere. The model estimates that bathymetric changes alone caused surface waters to cool by 3--4¿C in high latitudes and warm by 1--2¿C in low latitudes over the last 55 million years, which would account for as much as half (~4--5¿C) of the increase in the meridional sea surface temperature gradient during this time. Other changes include a cooling (~2¿C) of deep ocean waters, a warming of low-latitude intermediate waters (~2¿C), and decreases in Southern Ocean zonal sea surface temperature gradients.