Observations indicate that vertical diffusivity in the deep ocean is considerably enhanced over rough bathymetry and is very small elsewhere. Here we investigate effects of locally enhanced vertical diffusivity over rough bottom topography on the world ocean circulation by use of a coarse resolution ocean general circulation model. Vertical diffusivity is enhanced in the model, taking into account effects of internal tide breaking. For comparison, two cases of an experiment are carried out, where vertical diffusivity increases with depth without horizontal inhomogeneity. Horizontal distribution of deep upwelling is qualitatively different, depending on whether or not vertical diffusivity is horizontally inhomogeneous. Upwelling of Circumpolar Deep Water in the Pacific and Antarctic Bottom Water in the Atlantic is confined where vertical diffusivity is enhanced in the case of horizontally inhomogeneous vertical diffusivity, whereas it is horizontally uniform in the other case. This difference leads to different three-dimensional structure of the deep circulation. ¿ 1999 American Geophysical Union