simulation for mantle Helium-3 and Helium-4 according to the standard OCMIP-2 protocols. This simulation has two boundary conditions: (1) a loss term due to the sea-to-air flux of mantle helium, and (2) a source term due to emission of rich He-3/He-4 water along ocean ridges on the seafloor. Globally integrated, the source term amounts to 1000 moles of He-3 per year; regionally, sources are partitioned as a function of ridge position, length, and spreading rate).