Spatial-Temporal Variability and Sources of Lead (Pb) in the Indian Ocean and Asian Marginal Seas

Since North America and European countries phased out leaded gasoline, Asia has become the major contemporary lead (Pb) source to the marine environment, at first from leaded gasoline, but more recently from coal burning and other high-temperature industrial activities. Pb in the Indian Ocean remains relatively under-evaluated after & sim;2000 and is further complicated by various oceanic processes (e.g., monsoons, boundary exchange with particulates). Here, we present three annually resolved coral skeletal Pb isotope and concentration records from the central and eastern Indian Ocean (Salomon Atoll, 1989-2009; Diego Garcia Atoll, 1999-2009; and Phuket Island, 1945-2010), and synthesize published coral/sedimentary records to reconstruct the spatial-temporal variability of anthropogenic Pb around the region. Pb isotopes in all corals coherently fall along the mixing line between Asian aerosols and the natural crust. However, higher contributions of natural Pb are found in corals located in the coastal region than those in the open ocean, despite the greater contributions of anthropogenic Pb expected in coastal water near human emission sources. This geographical difference suggests that exchanges between dissolved Pb and natural particles at ocean boundaries significantly contribute to the Pb isotope compositions in regional seawater and are subsequently recorded in corals. The temporal variability of Pb concentrations in corals and sedimentary records signifies decreasing trends in Southeast Asia but increasing trends in South Asia. This study contributes new and timely Pb and Pb isotope data for the Indian Ocean and illustrates the importance of boundary exchange in marine Pb cycling.