Kinetics of Ce and Nd scavenging in Black Sea waters

Johan Schijf, Hein J.W. de Baar, Frank J. Millero

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9 Scopus citations


Mixing experiments were performed during Leg 5 of the 1988 Black Sea Expedition in order to learn more about the mechanism and kinetics of rare earth element (REE) scavenging at the oxic-anoxic interface of anoxic basins and, more specifically, in the suboxic zone of the Black Sea. Water from the depth of the dissolved REE maxima (300 dbar) was mixed in a thermostated reaction vessel with water from the depth of the particle maximum (PM) that had previously been equilibrated with the atmosphere. Subsamples were taken from the reaction vessel over a period of 24 h and analyzed for dissolved Ce (a redox reactive REE) and Nd (a non-redox reactive REE). During the first 2.5 h both Ce and Nd were removed from solution at a high rate, presumably as a result of adsorption onto fresh Mn and/or Fe oxides that formed during equilibration of the PM end-member with the atmosphere. The rates of Ce and Nd removal were approximately the same, suggesting that oxidative scavenging of Ce was of minor importance. After 2.5 h both Ce and Nd were released again at a rate much lower than that of the initial removal, presumably as a result of reductive dissolution of the Mn and/or Fe oxides onto which they were adsorbed. While this reductive dissolution may have been caused by sulfide that was introduced with the 300 dbar end-member, the results of a separate mixing experiment in the presence of a bio-inhibitor (formaldehyde) suggest that Mn and Fe reducing bacteria also played a significant role. The initial removal as well as the subsequent release of Ce and Nd were found to obey pseudo first-order kinetics.

Original languageEnglish (US)
Pages (from-to)345-359
Number of pages15
JournalMarine Chemistry
Issue number4
StatePublished - Jul 1994

ASJC Scopus subject areas

  • Oceanography
  • Chemistry(all)
  • Environmental Chemistry
  • Water Science and Technology


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