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@ARTICLE{Moschen:57266,
      author       = {Moschen, R. and Lücke, A. and Parplies, J. and Radtke, U.
                      and Schleser, G. H.},
      title        = {{T}ransfer and early diagenesis of biogenic silica oxygen
                      isotope signals during settling and sedimentation of diatoms
                      in a temperate freshwater lake ({L}ake {H}olzmaar,
                      {G}ermany)},
      journal      = {Geochimica et cosmochimica acta},
      volume       = {70},
      issn         = {0016-7037},
      address      = {New York, NY [u.a.]},
      publisher    = {Elsevier},
      reportid     = {PreJuSER-57266},
      pages        = {4367 - 4379},
      year         = {2006},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {We have investigated the transfer of oxygen isotope signals
                      of diatomaccous silica (delta P-18(diatom)) from the
                      epilimnion (0-7 m) through the hypolimnion to the lake
                      bottom (similar to 20 m) in freshwater Lake Holzmaar,
                      Germany. Sediment-traps were deployed in 2001 at depths of 7
                      and 16 m to harvest fresh diatoms every 28 days. The 7 m
                      trap collected diatoms from the epilimnion being the main
                      zone of primary production, while the 16 m trap collected
                      material already settled through the hypolimnion. Also a
                      bottom sediment sample was taken containing diatom frustules
                      from approximately the last 25 years. The delta O-18(diatom)
                      values of the 7 m trap varied from 29.4 parts per thousand
                      in spring/ autumn to 26.2 parts per thousand in summer
                      according to the temperature dependence of oxygen isotope
                      fractionation and represent the initial isotope signal in
                      this study. Remarkably, despite the short settling distance
                      delta(18)Odimom values of the 7 and the 16 m trap were
                      identical only during spring and autumn seasons while from
                      April to September delta O-18(diatom) values of the 16 m
                      trap were roughly similar to 1 parts per thousand enriched
                      in O-18 compared to those of the 7 m trap. Isotopic exchange
                      with the isotopically lighter water of the hypolimnion would
                      shift the delta O-18(diatom) value to lower values during
                      settling from 7 to 16 m excluding this process as a cause
                      for the deviation. Dissolution of opal during settling with
                      intact organic coatings of the diatom cells and near neutral
                      pH of the water should only cause a minor enrichment of the
                      16 m values. Nevertheless, opal from the bottom sediment was
                      found to be $2.5\%.$ enriched in O-18 compared to the
                      weighted average of the opal from the 7 m trap. Thus,
                      resuspension of bottom material must have contributed to the
                      intermediate delta O-18(diatom) signal of the 16 m trap
                      during summer. Dissolution experiments allowed further
                      investigation of the cause for the remarkably enriched delta
                      O-18(diatom), value of the bottom sediment. Experiments with
                      different fresh diatomaceous materials show an increase of
                      opaline O-18 at high pH values which is remarkably reduced
                      when organic coatings of the cells still exist or at near
                      neutral pH. In contrast, high-pH conditions do not affect
                      the delta O-18(diatom) values of sub-fossil and even fossil
                      opal. IR analyses show that the O-18 enrichment of the
                      sedimentary silica is associated with a decrease in Si-OH
                      groups and the formation of Si-O-Si linkages. This indicates
                      a silica dehydroxylation process as cause for the isotopic
                      enrichment of the bottom sediment. Silica dissolution and
                      dehydroxylation clearly induce a maturation process of the
                      diatom oxygen isotope signal presumably following an
                      exponential behaviour with a rapid initial phase of signal
                      alteration. The dynamics of this process is of particular
                      importance for the quantitative interpretation of
                      sedimentary delta O-18(diatom) values in terms of
                      palaeothermometry. (c) 2006 Elsevier Inc. All rights
                      reserved.},
      keywords     = {J (WoSType)},
      cin          = {ICG-V},
      ddc          = {550},
      cid          = {I:(DE-Juel1)VDB51},
      pnm          = {Geosysteme - Erde im Wandel},
      pid          = {G:(DE-Juel1)FUEK405},
      shelfmark    = {Geochemistry $\&$ Geophysics},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000240601800005},
      doi          = {10.1016/j.gca.2006.07.001},
      url          = {https://juser.fz-juelich.de/record/57266},
}