title: Recent distribution of lead in the Indian Ocean reflects the impact of regional emissions.
abstract: Humans have injected lead (Pb) massively into the earth surface environment in a temporally and spatially evolving pattern. A significant fraction is transported by the atmosphere into the surface ocean where we can observe its transport by ocean currents and sinking particles. This study of the Indian Ocean documents high Pb concentrations in the northern and tropical surface waters and extremely low Pb levels in the deep water. North of 20°S, dissolved Pb concentrations decrease from 42 to 82 pmol/kg in surface waters to 1.5-3.3 pmol/kg in deep waters. South of 20°S, surface water Pb concentrations decrease from 21 pmol/kg at 31°S to 7 pmol/kg at 62°S. This surface Pb concentration gradient reflects a southward decrease in anthropogenic Pb emissions. The upper waters of the north and central Indian Ocean have high Pb concentrations resulting from recent regional rapid industrialization and a late phase-out of leaded gasoline, and these concentrations are now higher than currently seen in the central North Pacific and North Atlantic oceans. The Antarctic sector of the Indian Ocean shows very low concentrations due to limited regional anthropogenic Pb emissions, high scavenging rates, and rapid vertical mixing, but Pb still occurs at higher levels than would have existed centuries ago. Penetration of Pb into the northern and central Indian Ocean thermocline waters is minimized by limited ventilation. Pb concentrations in the deep Indian Ocean are comparable to the other oceans at the same latitude, and deep waters of the central Indian Ocean match the lowest observed oceanic Pb concentrations.
authors.affiliation: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139;
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Echegoyen
authors.affiliation: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139; eaboyle@mit.edu.
authors.forename: Edward A
authors.initials: EA
authors.lastname: Boyle
authors.affiliation: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139; Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program in Oceanography, Woods Hole, MA 02543;
authors.forename: Jong-Mi
authors.initials: JM
authors.lastname: Lee
authors.affiliation: Atmosphere & Ocean Research Institute, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8564, Japan; and.
authors.forename: Toshitaka
authors.initials: T
authors.lastname: Gamo
authors.affiliation: Atmosphere & Ocean Research Institute, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8564, Japan; and.
authors.forename: Hajime
authors.initials: H
authors.lastname: Obata
authors.affiliation: Department of Environmental Science, Faculty of Science, Niigata University, Ikarashi-2-cho, Nishi-ku, Niigata 950-2181, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Norisuye
mesh_terms: D005843:Geography; D019156:Indian Ocean; D007854:Lead / Q000032:analysis*; D012623:Seawater / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014876:Water Pollution / Q000032:analysis*
chemical_list: D014874:Water Pollutants, Chemical; D007854:Lead
keywords: GEOTRACES; Indian Ocean; Pb content; anthropogenic emissions; lead