(F-11) and CCl2F2(F-12) have been measured at two locations in the eastern North Pacific Ocean to depths greater than 500 m. At both sites (46¿N, 125¿W off the Washington-Oregon coast and 50¿N, 140¿W in the Gulf of Alaska) the halomethane concentrations were found to fall off exponentially with increasing depth below the mixed layer. For F-11 at 50¿N, the surface concentration (3.2¿10-12 mol/l) was found to be in saturation equilibrium with the measured atmospheric concentration (190 pptv). The measure chlorofluoromethane profiles have been interpreted in terms of a one-dimensional model for the vertical diffusion/advection of an exponentially driven, conservative tracer into a bottomless ocean. In the appropriate limit of 'transient steady state' the projected profiles are simple exponentials described by an advective-diffusive scale depth H, which is a function of the vertical eddy diffusivity K, the upwelling velocity w, and the characteristic time &tgr; for the exponential growth of the tracer concentration at the boundary. At the two ocean locations studied from freon thermocline depth scales were in the range H≂120--140 m, with F-12 generally 10--20% deeper than F-11. At 50¿N the F-11 and F-12 vertical profiles gave consistent values of vertical diffusivity (Kz ~1.2--1.3 cm2 s-1) and upwelling velocity (w≂12--14 m yr-1). The model also allows a simple scaling from one exponentially driven, transient tracer (freon) to another (fossil fuel CO2), leading to a predicted mean depth of penetration of fossil fuel CO2 of approximately 300 m in the eastern North Pacific.