Iron oxidation in sediment cores (Site 1062) during six months of storage in the Ocean Drilling Program archive.

König, I., Lougear, A., Bruns, Peter, Grützner, Jens, Trautwein, A. X. and Dullo, Wolf-Christian (2000) Iron oxidation in sediment cores (Site 1062) during six months of storage in the Ocean Drilling Program archive. Open Access Proceedings of the Ocean Drilling Program: Scientific Results, 172 . Chapter 2.

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Abstract

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.

Document Type: Article
Keywords: Iron oxidation; sediment cores; Site 1062
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: No
Open Access Journal?: Yes
ISSN: 1096-7451
Projects: ODP
Expeditions/Models/Experiments:
Date Deposited: 25 Nov 2009 16:40
Last Modified: 27 Jul 2017 11:30
URI: http://oceanrep.geomar.de/id/eprint/7428

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