The distribution of lead concentrations and isotope compositions in the eastern Tropical Atlantic Ocean

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Bridgestock, Luke, Rehkämper, Mark, van de Flierdt, Tina, Paul, Maxence, Milne, Angela, Lohan, Maeve C., Achterberg, Eric P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2018
• Subjects: North Atlantic Deep Water; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/41849/; https://oceanrep.geomar.de/id/eprint/41849/1/1-s2.0-S001670371830036X-main.pdf; https://oceanrep.geomar.de/id/eprint/41849/7/Bridgestock_Suppl1.docx; https://oceanrep.geomar.de/id/eprint/41849/8/Bridgestock_Suppl2.xlsx; https://doi.org/10.1016/j.gca.2018.01.018

Highlights • Pb concentrations and isotope ratios presented for GEOTRACES section GA06. • Northern and southern hemisphere water masses have distinct Pb isotope ratios. • Pb isotope ratios consistent with ventilation timescales of northern water masses. • Mixing complicates interpretation of Pb distributions in southern water masses. Abstract Anthropogenic emissions have dominated marine Pb sources during the past century. Here we present Pb concentrations and isotope compositions for ocean depth profiles collected in the eastern Tropical Atlantic Ocean (GEOTRACES section GA06), to trace the transfer of anthropogenic Pb into the ocean interior. Variations in Pb concentration and isotope composition were associated with changes in hydrography. Water masses ventilated in the southern hemisphere generally featured lower 206Pb/207Pb and 208Pb/207Pb ratios than those ventilated in the northern hemisphere, in accordance with Pb isotope data of historic anthropogenic Pb emissions. The distributions of Pb concentrations and isotope compositions in northern sourced waters were consistent with differences in their ventilation timescales. For example, a Pb concentration maximum at intermediate depth (600–900 m, 35 pmol kg−1) in waters sourced from the Irminger/Labrador Seas, is associated with Pb isotope compositions (206Pb/207Pb = 1.1818–1.1824, 208Pb/207Pb = 2.4472–2.4483) indicative of northern hemispheric emissions during the 1950s and 1960s close to peak leaded petrol usage, and a transit time of ∼50–60 years. In contrast, North Atlantic Deep Water (2000–4000 m water depth) featured lower Pb concentrations and isotope compositions (206Pb/207Pb = 1.1762–1.184, 208Pb/207Pb = 2.4482–2.4545) indicative of northern hemispheric emissions during the 1910s and 1930s and a transit time of ∼80–100 years. This supports the notion that transient anthropogenic Pb inputs are predominantly transferred into the ocean interior by water mass transport. However, the interpretation of Pb concentration and isotope composition ...