Following Duce: The Decadal Evolution of Pb and Pb Isotope Delivery to the Ocean by Atmospheric Aerosols

One of Bob Duce's important contributions to our science was enabling Turekian and Patterson's studies of Pb-210 and Pb in atmospheric aerosols in AEROCE and other sampling programs. This work was important for several reasons. One reason common to all aerosol work was of course in using Pb-210 in order to get an estimate for aerosol deposition into the ocean: because studies of Pb-210 fallout and ocean mixed layer chemistry allows for an estimate of Pb-210 fluxes into the ocean, measurements of the ratio any other aerosol property to Pb-210 in the aerosols allows for an estimate of the deposition rate for that property. But the measurement of combined Pb-210 and Pb concentrations also enabled Patterson to obtain the first global view of anthropogenic Pb dispersal, confounding the deniers who claimed that anthropogenic Pb must be small potatoes compared to natural sources such as volcanoes. As someone following in Patterson's footsteps, my research group has been able to document the decadal consequences of leaded gasoline phaseout from the mid-1970's to the present. In the North Atlantic ocean, Pb has been decreasing consistently in the upper km because of US and European leaded gasoline phaseout. The difference in the US-European phaseout rapidity is reflected in the increasing Europeanization of Pb isotope ratios in the Atlantic Ocean during the 1990's and early 2000's. We can see North American and European Pb in the deep water carried into the South Atlantic by NADW. In the North Pacific, US, Japanese, and Canadian gasoline Pb is being replaced by coal Pb from south Asia. The later-industrializing and later-Pb-gas-phaseout countries of the Indian Ocean have now made it the ocean with the highest surface Pb concentrations. The evolution from dominant Pb-gas to dominant coal-combustion sources in the southern Indian ocean is documented in the vertical distribution of Pb isotopes.