The age of water in the World Ocean is studied using a passive age tracer introduced into a global ocean model. Additional information is derived from a transient “dye” tracer that tracks the time-dependent spreading of surface waters into the model ocean interior. Of particular interest is the nature of ocean ventilation over the 10–100-yr timescale, as well as the simulated age of deep and bottom water masses. In the upper model levels young water is found to correspond with regions of convergence (and downwelling) in the surface Ekman layer. Upwelling and convection are both shown to age the upper ocean by entraining older waters into the surface mixed layer. In the deep model levels, water age varies greatly between oceans, with young water found in convectively active regions (in the North Atlantic and in the Ross and Weddell Seas), and old water found in the deep North Pacific. The oldest water mass mixture (located at 2228-m depth in the western Pacific Ocean) is dated at 1494 years, made ... Abstract The age of water in the World Ocean is studied using a passive age tracer introduced into a global ocean model. Additional information is derived from a transient “dye” tracer that tracks the time-dependent spreading of surface waters into the model ocean interior. Of particular interest is the nature of ocean ventilation over the 10–100-yr timescale, as well as the simulated age of deep and bottom water masses. In the upper model levels young water is found to correspond with regions of convergence (and downwelling) in the surface Ekman layer. Upwelling and convection are both shown to age the upper ocean by entraining older waters into the surface mixed layer. In the deep model levels, water age varies greatly between oceans, with young water found in convectively active regions (in the North Atlantic and in the Ross and Weddell Seas), and old water found in the deep North Pacific. The oldest water mass mixture (located at 2228-m depth in the western Pacific Ocean) is dated at 1494 years, made ...