Dissolved lead in the deep Southeast Pacific Ocean: results of the 2013 US GEOTRACES cruise

Lead (Pb) in the modern ocean is dominated by anthropogenic Pb, which has been evidenced by highly elevated seawater Pb concentrations and Pb stable isotope ratios (²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb) altered from pre-anthropogenic values. A number of studies have shown the human impact on oceanic Pb in many parts of the world ocean, but little Pb data has been available for the Southeast Pacific Ocean.

In this presentation, we will show the dissolved Pb (<0.2µm) results from the US GEOTRACES cruise in October – December 2013, which sailed from Manta, Ecuador, to Tahiti along around 12 degrees south. Dissolved Pb concentrations from all 36 surface stations and deep (>1000m) Pb profiles from 18 stations will be presented, and the results will be also compared to our unpublished data from the BiG RAPA cruise in 2010, whose cruise track from Arica, Peru, to Easter Island is slightly south of the US GEOTRACES cruise. The BiG RAPA data showed that dissolved Pb concentrations of the southeast Pacific Ocean are relatively low, varying in the range of 8-20 pmol/kg at the surface with a slight maximum (14-22 pmol/kg) at around 400m depth, and 2-10 pmol/kg in deep waters below 1000m depth. The Pb concentrations were found to be higher at a marginal station off Peru, reaching 45 pmol/kg at the surface and 65 pmol/kg in the subsurface maximum at 150m depth, and varying between 17 and 23 pmol/kg in deep waters.

Our dataset, along with the results from the BiG RAPA cruise, will provide the first overview on the dissolved Pb distribution of the southeast Pacific Ocean, which will further our understanding on the human impact on the global ocean.