Sources of lead in a Tibetan glacier since the Stone Age

The Tibetan Plateau glaciers, among the world’s most remote and pristine places, provide water to millions and play a vital environmental role. We measured the lead isotopic composition in a dusty ice core from the Guliya ice cap in northwest Tibet, from approximately 36 thousand years Before Present (Stone Age) to 2015, to determine the onset and sources of anthropogenic lead. Despite the dust-laden nature of the core, a clear change in the lead isotope signature to below Stone Age levels started in 1949 followed by a rapid decrease in 1960 and an even more rapid decrease in 1974 indicating the first emergence of anthropogenic lead. Accurate isotopic lead measurements allowed us to better, and more sensitively, quantify sources using a Bayesian mixing model. Chinese gasoline was the primary anthropogenic source surpassing natural contributions in the 2000s until 2007 when emissions from leaded gasoline decreased and those from coal and lead-zinc ores increased.