Historical changes in 239Pu and 240Pu sources in sedimentary records in the East China Sea: Implications for provenance and transportation

Jinlong Wang, Mark Baskaran, Xiaolin Hou, Jinzhou Du, Jing Zhang

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    Abstract

    Concentrations and isotopic compositions of plutonium (Pu) are widely used for its source identification and to determine transport processes of Pu-associated particulate matter and water. We investigated the concentrations of 239Pu and 240Pu and their ratios in a number of sediment samples from the East China Sea (ECS) collected in the summer of 2013 (August 6–28). The 239+240Pu activity concentrations in surface sediment samples were found to range between 0.048 and 0.492 Bqkg−1and the 240Pu/239Pu atom ratios showed a similar trend as that of the 239,240Pu activities; the Pu atom ratios ranged from 0.158 to 0.297 and were mostly higher than the mean global fallout value of 0.18. The 239,240Pu inventories in the ECS varied widely, from 2 to 807 Bqm−2, with the highest values commonly found in the coastal areas. In the Yangtze Estuary, the mean 239+240Pu activity concentration is close to the estimated value of the suspended material from the Yangtze River catchment (0.18 Bqkg−1), and the 240Pu/239Pu atom ratio was found to be ∼0.18, which indicates that the Yangtze River input is the dominant source of Pu for this area. The total annual Yangtze River input of 239+240Pu was estimated to be 2.4 ×1010Bq, which is small compared to the total amount of 239+240Pu buried, 3.1 ×1013Bq in the whole ECS. The Pacific Proving Ground input appears to be the dominant source of Pu to the ECS, accounting for 45%–52% of the total inventory. The fractional amount of 239+240Pu scavenged from the total 239+240Pu transported by the Kuroshio Current (KC) and Taiwan Warm Current (TWC) into ECS sediments is estimated to be ∼10%. Our study shows that the 240Pu/239Pu atom ratio is useful not only to obtain a better insight of the biogeochemistry influenced by the KC, but also to trace the long-range transport of other particle-reactive species. Besides, the sedimentation rates obtained based on the penetration depths of 239+240Pu and vertical profiles of excess 210Pb agree within uncertainties, which suggests that 239+240Pu can potentially be used as a chronostratigraphic time marker in the marine environment.
    Original languageEnglish
    JournalEarth and Planetary Science Letters
    Volume466
    Pages (from-to)32-42
    ISSN0012-821X
    DOIs
    Publication statusPublished - 2017

    Keywords

    • East China Sea
    • Plutonium
    • Isotopic ratio
    • Sediment
    • Transportation
    • Mass balance

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