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 (Flegal et al., 2013, https://doi.org/10.1080/10643389.2012.671738; Lee et al., 2014, https://doi.org/10.1016/j.epsl.2014.04.030). Pb in the Indian Ocean remains relatively under‐evaluated after ∼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. Plain Language Summary: Since the industrial revolution, anthropogenic lead (Pb) emissions from human activities, such as coal burning and leaded‐gasoline combustion, have changed the distribution of Pb in the ocean. In this study, we investigate the spatial and temporal variations in coral Pb records in the Indian Ocean and Southeast Asia and compare them to previously reported Asian Pb records from coral and sediment cores. Interestingly, an excellent mixing line between coral Pb isotopes is observed, which reflects aerosols with industrial Pb and natural Pb. In addition, through the compilation of Pb levels and anomalies in Asian coral and sediment cores, three trends of Pb level evolution were identified, that is, an increasing trend in Southeast Asia, a decreasing trend in South Asia, and both increasing/decreasing trends in East Asia. It is important to note that the rising Pb concentrations in waters off of South Asia in the 2000s remind us of a need to continue to pay attention to Pb exposure in the environment. Key Points: Higher natural Pb contributions in Southeast Asian coastal corals than those in the open Indian Ocean reflect seawater‐particle exchangeCoral Pb isotope ratios indicate varying degrees of mixing between natural crustal Pb and anthropogenic Asian aerosol PbPb concentration anomalies in coral and marine sediment cores show three distinct trends in South, Southeast, and East Asia since 2000 [ABSTRACT FROM AUTHOR]