Publication Date:
2024-01-09
Description:
Changes in bulk sediment Fe(II)/Fe(III) ratio and in the distribution of iron among different minerals as a result of Ocean Drilling Program archive storage in the Bremen Core Repository were investigated using Mössbauer spectroscopy. Massive Fe(II) to Fe(III) oxidation, which involved between 24% and 45% of the initial Fe(II), occurred within only 6 months of refrigerated storage. Prior to archive storage, 〉95% of the Fe(II) in the sediment samples under investigation was structural iron in silicate minerals. Hence, virtually the entire oxidation process took place within silicate mineral lattices, and the sediment mineral assemblage was not changed in this case. Nevertheless, the observed oxidation of the comparatively shielded silicate lattice Fe(II) suggests that Fe(II) bound in authigenic carbonates, phosphates, or sulfides - such as that found in many marine sediments - would likely be oxidized at least as fast. Those minerals, however, would be replaced by Fe(III)-bearing oxides and oxyhydroxides, which implies a change of sediment composition, and thus, of various sediment properties, including the magnetic signal, within a few months of storage.
Furthermore, changes in the silicate lattice Fe(II)/Fe(III) ratio during storage, such as those reported here, also signify loss of information. This is because oxidation of the structural Fe(II) upon contact with atmospheric oxygen may occur only inasmuch as the inverse Fe(III)-Fe(II) redox transition has taken place in the seabed. Therefore, the reversible shift, if it were measured under controlled reoxidation in the laboratory, may suggest the chemical stress that was suffered by the iron oxide minerals at the ocean bottom. Concerning Site 1062, this process might help to judge both the authenticity of magnetic field excursion records and the lithostratigraphic value of red lutites at given sediment depths. Although the nature and extent of information loss or alteration during storage depend on sediment type, the reported observations emphasize the need for special sample protection with respect to properties that might be affected.
Keywords:
172-1062A; Age model; Blake-Bahama Outer Ridge, North Atlantic Ocean; DEPTH, sediment/rock; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Iron II, ferrous iron; Iron III, ferric iron; Joides Resolution; Leg172; Ocean Drilling Program; ODP; Sample code/label; Sample comment
Type:
Dataset
Format:
text/tab-separated-values, 144 data points
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