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  • 1
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    A geochemical model of the Peru Basin deep-sea floor and the response of the system to technical impacts (2001)
    Pergamon Press
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 48 . pp. 3737-3756.
    Details
    Publication Date: 2020-08-05
    Description: A geochemical model of the Peru Basin deep-sea floor, based on an extensive set of field data as well as on numerical simulations, is presented. The model takes into account the vertical oscillations of the redox zonation that occur in response to both long-term (glacial/interglacial) and short-term (El Niño Southern Oscillation (ENSO) time scale) variations in the depositional flux of organic matter. Field evidence of reaction between the pore water NO3− and an oxidizable fraction of the structural Fe(II) in the clay mineral content of the deep-sea sediments is provided. The conditions of formation and destruction of reactive clay Fe(II) layers in the sea floor are defined, whereby a new paleo-redox proxy is established. Transitional NO3− profile shapes are explained by periodic contractions and expansions of the oxic zone (ocean bottom respiration) on the ENSO time scale. The near-surface oscillations of the oxic–suboxic boundary constitute a redox pump mechanism of major importance with respect to diagenetic trace metal enrichments and manganese nodule formation, which may account for the particularly high nodule growth rates in this ocean basin. These conditions are due to the similar depth ranges of both the O2 penetration in the sea floor and the bioturbated high reactivity surface layer (HRSL), all against the background of ENSO-related large variations in depositional Corg flux. Removal of the HRSL in the course of deep-sea mining would result in a massive expansion of the oxic surface layer and, thus, the shut down of the near-surface redox pump for centuries, which is demonstrated by numerical modeling.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0967-0645(01)00065-0
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    New procedure for determining reactive Fe(III) and Fe(II) minerals in sediments (2003)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 38 (8). pp. 1803-1812.
    Details
    Publication Date: 2019-09-23
    Description: Sediments from the River Elbe estuary and incubated sediments were extracted with 1 N HCI for 24 h at room temperature. The extracted ferric and ferrous iron was determined with DC and AC polarography. Acid-volatile sulfide was determined from H2S trapped in aqueous zinc acetate solution. Analysis of sediment samples and extraction residues with Mossbauer spectroscopy demonstrated that the Fe oxidation state was conserved during extraction and polarographic determination, siderite and vivianite were completely dissolved, and Fe(II) in chlorite was partially extracted with HCl. Incubation experiments showed that extractable Fe was almost completely oxidized to Fe(III) at the oxic sediment surface and reduced to Fe(II) in deeper anoxic layers within a few weeks. Reactive Fe(III), i.e. that fraction of Fe which was reducible on the time scale of the incubation experiment, was completely extracted with HCl.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lo.1993.38.8.1803
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Reactive Fe (II) layers in deep-sea sediments (1999)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 63 (10). pp. 1517-1526.
    Details
    Publication Date: 2017-08-25
    Description: The percentage of the structural Fe(II) in clay minerals that is readily oxidized to Fe(III) upon contact with atmospheric oxygen was determined across the downcore tan–green color change in Peru Basin sediments. This latent fraction of reactive Fe(II) was only found in the green strata, where it proved to be large enough to constitute a deep reaction layer with respect to the pore water O2 and NO3−. Large variations were detected in the proportion of the reactive Fe(II) concentration to the organic matter content along core profiles. Hence, the commonly observed tan–green color change in marine sediments marks the top of a reactive Fe(II) layer, which may represent the major barrier to the movement of oxidation fronts in pelagic subsurface sediments. This is also demonstrated by numerical model simulations. The findings imply that geochemical barriers to pore water oxidation fronts form diagenetically in the sea floor wherever the stage of iron reduction is reached, provided that the sediments contain a significant amount of structural iron in clay minerals.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0016-7037(99)00104-0
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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