The carbon-14 activity of oceanic materials indicates that the mixing half-time for carbon between the atmosphere and ocean surface waters is one or two decades, while the turnover time for the ocean as a whole is several hundred years. This conclusion is consistent with estimates based on the measured decrease in carbon-14 specific activity of wood grown in recent years compared with 19th century wood. DOI: 10.1111/j.2153-3490.1957.tb01850.x