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      Lead isotope exchange between dissolved and fluvial particulate matter: a laboratory study from the Johor River estuary

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          Abstract

          Atmospheric aerosols are the dominant source of Pb to the modern marine environment, and as a result, in most regions of the ocean the Pb isotopic composition of dissolved Pb in the surface ocean (and in corals) matches that of the regional aerosols. In the Singapore Strait, however, there is a large offset between seawater dissolved and coral Pb isotopes and that of the regional aerosols. We propose that this difference results from isotope exchange between dissolved Pb supplied by anthropogenic aerosol deposition and adsorbed natural crustal Pb on weathered particles delivered to the ocean by coastal rivers. To investigate this issue, Pb isotope exchange was assessed through a closed-system exchange experiment using estuarine waters collected at the Johor River mouth (which discharges to the Singapore Strait). During the experiment, a known amount of dissolved Pb with the isotopic composition of NBS-981 ( 206Pb/ 207Pb = 1.093) was spiked into the unfiltered Johor water (dissolved and particulate 206Pb/ 207Pb = 1.199) and the changing isotopic composition of the dissolved Pb was monitored. The mixing ratio of the estuarine and spike Pb should have produced a dissolved 206Pb/ 207Pb isotopic composition of 1.161, but within a week, the 206Pb/ 207Pb in the water increased to 1.190 and continued to increase to 1.197 during the next two months without significant changes of the dissolved Pb concentration. The kinetics of isotope exchange was assessed using a simple K d model, which assumes multiple sub-reservoirs within the particulate matter with different exchange rate constants. The K d model reproduced 56% of the observed Pb isotope variance. Both the closed-system experiment and field measurements imply that isotope exchange can be an important mechanism for controlling Pb and Pb isotopes in coastal waters. A similar process may occur for other trace elements.

          This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.

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          Author and article information

          Journal
          Philos Trans A Math Phys Eng Sci
          Philos Trans A Math Phys Eng Sci
          RSTA
          roypta
          Philosophical transactions. Series A, Mathematical, physical, and engineering sciences
          The Royal Society
          1364-503X
          1471-2962
          28 November 2016
          : 374
          : 2081 , Discussion meeting issue ‘Biological and climatic impacts of ocean trace element chemistry’ organised and edited by Gideon Henderson, Ed Boyle, Maeve Lohan, Micha Rijkenberg and Géraldine Sarthou
          : 20160054
          Affiliations
          [1 ] Singapore-MIT Alliance on Research and Technology, Center of Environmental Sensing and Modelling , 1 CREATE Way, #09-03 CREATE Tower, 138602 Singapore
          [2 ] Asian School of the Environment, Nanyang Technological University , 50 Nanyang Avenue, 639798 Singapore
          [3 ] Earth Observatory of Singapore, Nanyang Technological University , 50 Nanyang Avenue, 639798 Singapore
          [4 ] Department of Earth, Atmospheric, and Planetary Sciences, E25-619, Massachusetts Institute of Technology , Cambridge, MA 02139, USA
          [5 ] Ocean Sciences Department, University of Santa Cruz , 1156 High Street, Santa Cruz, CA 95064, USA
          Author notes

          One contribution of 20 to a discussion meeting issue ‘ Biological and climatic impacts of ocean trace element chemistry’.

          Author information
          http://orcid.org/0000-0002-6394-1866
          Article
          PMC5069536 PMC5069536 5069536 rsta20160054
          10.1098/rsta.2016.0054
          5069536
          29035266
          b1c93cf8-2ad5-46cc-813e-c1f517363bd7
          © 2016 The Author(s)

          Published by the Royal Society. All rights reserved.

          History
          : 16 August 2016
          Funding
          Funded by: Singapore National Research Foundation (NRF);
          Categories
          1005
          78
          140
          Articles
          Research Article
          Custom metadata
          November 28, 2016

          isotope exchange,Pb,Pb isotopes,estuaries,particles,Singapore
          isotope exchange, Pb, Pb isotopes, estuaries, particles, Singapore

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