Lead from Carthaginian and Roman Spanish mines isotopically identified in Greenland ice dated from 600 BC to 300 AD

The pollution history of the atmosphere of the Northern Hemisphere is recorded in the levels of heavy metal impurities in Greenland ice. The possibility also exists of using natural variations in the abundances of lead isotopes to trace the source of this pollution. Lead isotopes have now been measured in ancient Greenland ice with a lead concentration as low as 0.9 pg/g. The results show a depression in the Pb-206/Pb-207 ratio between 600 B.C. and 300 A.D., giving unequivocal evidence of early large-scale atmospheric pollution by this toxic metal. This ratio changes from similar to 1.201 in similar to 8-kyr-old ice to similar to 1.183 about 2 kyr ago. Isotopic systematics point to the mining districts ir southwest and southeast Spain as the dominant sources of this lead, giving quantitative evidence of the importance of these mining districts to the Carthaginian and Roman civilizations. Lead with a Rio Tinto-type signature represents similar to 70% of the lead found in Greenland ice between similar to 150 B.C. and 50 A.D. after correcting for the contribution from rock dust indexed to aluminium concentrations.