Industrial-era lead and mercury contamination in southern Greenland implicates North American sources

Highlights: • Lead (Pb) isotope and mercury (Hg) data are presented from southern Greenland. • Two Pb geological sources (local and regional) and a pollution source were found. • Atmospheric Hg and Pb pollution increase from the mid-18th century. • Hg and Pb pollution show a similar trend to combustible consumption in North America. • Pb isotopic data does not allow separation between sources in the USA and CA. To study the long-range transport of atmospheric pollutants from lower latitude industrial areas to the Arctic, we analysed a peat core spanning the last ~ 700 cal. yr (~ 1300–2000 CE) from southern Greenland, an area sensitive to atmospheric pollution from North American and Eurasian sources. A previous investigation conducted in the same location recorded atmospheric lead (Pb) pollution after ~ 1845, with peak values recorded in the 1970s, and concluded that a North American source was most likely. To confirm the origin of the lead, we present new Pb isotope data from Sandhavn, together with a high-resolution record for mercury (Hg) deposition. Results demonstrate that the mercury accumulation rate has steadily increased since the beginning of the 19th century, with maximum values of 9.3 μg m^{− 2} yr⁻¹ recorded ~ 1940. Lead isotopic ratios show two mixing lines: one which represents inputs from local and regional geogenic sources, and another that comprises regional geogenic and pollution sources. Detrending the Pb isotopic ratio record (thereby extracting the effect of the geogenic mixing) has enabled us to reconstruct a detailed chronology of metal pollution. The first sustained decrease in Pb isotope signals is recorded as beginning ~ 1740–1780 with the lowest values (indicating the highest pollution signature) dated to ~ 1960–1970. The ²⁰⁶Pb/²⁰⁷Pb ratio of excess Pb (measuring 1.222, and reflecting pollution-generated Pb), when compared with the Pb isotopic composition of the Sandhavn peat record since the 19th century and the timing of Pb enrichments, clearly points to the dominance of pollution sources from North America, although it did not prove possible to further differentiate the emissions sources geographically.