Lead isotopes trace interhemispheric transport of water masses and pollution to the tropical western North Atlantic Ocean
File(s)
Accepted version
Supporting information
Author(s)
Type
Journal Article
Abstract
The use of leaded gasoline significantly impacted North Atlantic seawater during the 20th century, leaving a legacy of pollution that remains traceable despite the global ban reached in 2021. This study presents new Pb concentration and isotope data from four depth profiles in the western tropical North Atlantic along Leg 2 of GEOTRACES section GA02 from 31.7°N to 1.2°N. The data capture atmospheric inputs and water masses from both hemispheres, revealing latitudinal variability in Pb isotope signatures in the upper part of the water column. In surface waters, low 206Pb/207Pb ratios (1.166–1.173) indicate South American and North African anthropogenic sources at the southern stations, and higher 206Pb/207Pb ratios (1.174–1.179) reflect anthropogenic North American and natural North African mineral dust inputs at the northern stations. A comparison of North Atlantic surface water data for 1981–1999 and 2010–2014 reveals distinct shifts in Pb concentrations and isotope ratios, confirming the effectiveness of Pb isotopes as tracers for identifying and tracking Pb sources over time in the North Atlantic. The Pb concentrations and isotopic signatures of central water masses (formed 4–15 years ago relative to sampling time) and intermediate water masses (formed 20–50 years ago) are consistent with the expected atmospheric Pb sources at the time and location of their formation, emphasizing the influence of both spatial and temporal variations in atmospheric Pb deposition. However, in the intermediate layer, where northern- and southern-sourced water masses mix, a deviation of the Pb concentration from the expected water mass mixing trend suggests removal of some dissolved Pb by particles. North Atlantic Deep Water exhibits persistent anthropogenic Pb signals from historical US and European emissions (20–30 years ago), while bottom waters within a nepheloid layer show evidence of natural Pb release from sediments. Overall, these findings suggest that Pb isotope ratios predominantly act as conservative tracers of water masses in the strongly advective western tropical North Atlantic Ocean.
Date Acceptance
2026-10-07
Citation
Geochimica et Cosmochimica Acta
ISSN
0016-7037
Publisher
Elsevier
Journal / Book Title
Geochimica et Cosmochimica Acta
Copyright Statement
Copyright This paper is embargoed until publication. Once published the Version of Record (VoR) will be available on immediate open access.
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Publication Status
Accepted