Earth and Planetary Science Letters, 82 (1987) 289-304 289 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands [61 Lead in corals: reconstruction of historical industrial fluxes to the surface ocean Glen T. Shen * and Edward A. Boyle Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 01239 (U.S.A.) Received October 1, 1986; revised version received January 9, 1987 Twentieth century environmental lead chronologies for the western North Atlantic, Pacific, and Indian Oceans have been reconstructed from annually-banded scleractinian corals. Measurements of lattice-bound Pb in sequential coral bands reveal temporal changes in surface water Pb concentrations and Pb isotopic distributions. Perturbations are observable in all specimens studied, attesting to global augmentation of environmental Pb by industrialization. In the western North Atlantic, Pb perturbations have occurred in direct response to the American industrial revolution and the subsequent introduction and phasing-out of alkyl Pb additives in gasoline. Surface ocean conditions near Bermuda may be reliably reconstructed from the coral data via a lead distribution coefficient of 2.3 for the species, Diploria strigosa. Based on 21°pb measurements, a similar distribution coefficient may be characteristic of corals in general. Surface Pb concentrations in the pre-industrial Sargasso Sea were about 15-20 pM. Concentrations rose to near 90 pM by 1923 as a result of metals manufacture and fossil fuel combustion. Beginning in the late 1940's, increased utilization of leaded gasoline eventually led to a peak concentration of 240 pM in 1971, representing an approximate 15-fold increase over background. Surface ocean concentrations are presently declining rapidly (128 pM in 1984) as a result of curtailed alkyl Pb usage. Lead isotopic shifts parallel the concentration record indicating that characteristic industrial and alkyl Pb source signatures have not changed appreciably in time. Industrial releases recorded in the Florida Keys reflect a weaker source and evidence of recirculated Pb (5-6 years old) from the North Atlantic subtropical gyre. An inferred background concentration of 38 pM suggests influence of shelf and/or resuspended inputs of Pb to these coastal waters. In remote areas of the South Pacific and Indian Oceans, industrial signals are fainter and the corals studied much younger than their Atlantic counterparts. Contemporary Pb concentrations implied by coral measurements (assuming K D = 2.3) are 40-50 pM for surface waters near Tutuila and Galapagos in the South Pacific, and 25-29 pM near Mauritius in the Indian Ocean. A single coral band from Fiji (1920 + 5 yr) implies a pre-industrial surface water concentration of 16-19 pM Pb for the South Pacific. In view of reported surface water measurements and the North Atlantic coral data, the Pacific coral extrapolations may be slightly high. This could be a result of small variations in K o among different coral genera, or incorporation of diagenetic Pb by corals sampled in coastal environments. 1. Introduction Over the past two decades, convincing evidence of global environmental contamination by in- dustrial lead has accumulated. Murozumi et al. [1] documented historic increases of lead in snow strata cored in Greenland and Antarctica in 1969. More recent snow and ice core determinations from both hemispheres have confirmed their origi- nal findings (see review by Wolff and Peel [2]). Contamination continues to hamper measurement efforts in the most pristine locations, however, * Present address: Lamont-Doherty Geological Observatory Palisades, NY, 10964, U.S.A. particularly in the case of ancient samples. Extension of anthropogenic lead mapping to the oceans succeeded more recently when Schaule and Patterson [3] overcame sampling difficulties in 1976. Together with newer oceanic data by Flegal, Schaule, and Patterson [4-6] and Boyle et al. [7], and atmospheric flux measurements by Settle, Patterson and coworkers [8,9] and Jickells, Church and others [10,11], effects of industrial proximity and meteorology have been observed. Eolian de- livery of stable lead parallels that of 21°Pb [7,12,13], but the stable Pb source function differs from that of 21°pb and has evolved over time. The transient nature of this flux leads to the application of stable Pb as an oceanic chemical tracer to comple- 0012-821X/87/$03.50 © 1987 Elsevier Science Publishers B.V.