Surface water in the ocean invades the subsurface vertically, against the density gradient, and along constant-density surfaces from surface outcrops in high latitudes. We present dissolved argon data that distinguishes a diapycnally ventilated upper thermocline in the equatorial Pacific versus an isopycnally ventilated subtropical location near Hawaii. The lower thermocline is shown to be isopycnally ventilated at both locations, in contrast with theoretical and model predictions.