Dissolved Pb and Pb isotopes in the North Atlantic from the GEOVIDE transect (GEOTRACES GA-01) and their decadal evolution

Abstract

During the 2014 GEOVIDE transect, seawater samples were collected for dissolved Pb and Pb isotope analysis. These samples provide a high resolution <q>snapshot</q> of the source regions for the present Pb distribution in the North Atlantic Ocean. Some of these stations were previously occupied for Pb from as early as 1981, and we compare the 2014 data with these older data some of which are reported here for the first time. Lead concentrations were highest in subsurface Mediterranean Water (MW) near the coast of Portugal, which agrees well with other recent observations by the U.S. GEOTRACES program (Noble et al., 2015). The recently formed Labrador Sea Water (LSW) between Greenland and Nova Scotia is much lower in Pb concentration than the older LSW found in the Western European Basin due to decreases in Pb emissions into the atmosphere during the past 20 years. Comparison of North Atlantic data from 1989&amp;ndash;2014 shows decreasing Pb concentrations consistent with decreased anthropogenic inputs, active scavenging, and advection/convection. The nearly-homogenous isotopic composition of northern North Atlantic seawater implies that the relative proportions of U.S. and European Pb sources to the ocean have been relatively uniform during the past two decades. Using our measurements in conjunction with emissions inventories, we support the findings of previous atmospheric analyses that up to 50&amp;thinsp;% of the Pb deposited to the ocean in 2014 was natural, although it remains unclear if that natural dust is from the mid- or high-latitudes.