Decline of anthropogenic lead in South Atlantic Ocean surface waters from 1990 to 2011: New constraints from concentration and isotope data

Anthropogenic emissions have severely perturbed the marine biogeochemical cycle of lead (Pb). Here, we present new Pb concentration and isotope data for surface seawater from GEOTRACES section GA02, sampled in the western South Atlantic in 2011. The South Atlantic is divided into three hydrographic zones: equatorial (0-20 degrees S), subtropical (20-40 degrees S), and subantarctic (40-60 degrees S). The equatorial zone is dominated by previously deposited Pb transported by surface currents. The subtropical zone largely reflects anthropogenic Pb emissions from South America, whilst the subantarctic zone presents a mixture of South American anthropogenic Pb and natural Pb from Patagonian dust. The mean Pb concentration of 16.7 +/- 3.8 pmol/kg is 34 % lower than in the 1990s, mostly driven by changes in the subtropical zone, with the fraction of natural Pb increasing from 24 % to 36 % between 1996 and 2011. Although anthropogenic Pb remains predominant, these findings demonstrate the effectiveness of policies that banned leaded gasoline.

Automated summary

Anthropogenic emissions have had a significant impact on the marine biogeochemical cycle of lead (Pb). New data from surface seawater in the western South Atlantic in 2011 reveal that the equatorial zone is dominated by previously deposited Pb, while the subtropical zone reflects anthropogenic Pb emissions from South America and the subantarctic zone presents a mixture of South American anthropogenic Pb and natural Pb from Patagonian dust. The average Pb concentration has decreased by 34% since the 1990s, primarily driven by changes in the subtropical zone and an increase in the fraction of natural Pb.