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| Titel |
Experimental study of abiotic and microbial Fe-mineral transformations to understand magnetic enhancement during pedogenesis |
| VerfasserIn |
Jessica Till, Yohan Guyodo, France Lagroix, Pierre Bonville, Georges Ona-Nguema, Nicolas Menguy, Guillaume Morin |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250081408
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| Zusammenfassung |
| The phenomenon of magnetic enhancement in many soil types has been recognized for
several years, but the question of whether the enhancement process is primarily driven by
microbial activity or abiotic processes is still unresolved. We present results from an on-going
interdisciplinary experimental study of possible pathways of magnetic enhancement
during pedogenesis of loess-derived soils. Synthetic nanoparticle preparations of the
oxyhydroxides goethite and lepidocrocite were chosen as Fe-rich precursor phases. Abiotic
alteration was achieved by heating in a controlled atmosphere, under either oxidizing or
reducing conditions. Heating-induced dehydration reactions in lepidocrocite produce
superparamagnetic magnetite or maghemite with a characteristic nanoporous structure, while
dehydration of nanogoethite produced pseudo-morphed hematite, which converts to
magnetite during heating in a reducing atmosphere. The abiotic alteration experiments are
compared with preliminary results from bioreduction experiments using the dissimilatory
Fe-reducing bacteria Shewanella putrefaciens in both the synthetic minerals and in natural
loess, soil and paleosol materials. The magnetic properties, microstructure, and morphology
of the reaction products were characterized with a combination of low-temperature magnetic
properties, Mössbauer spectroscopy, high-resolution TEM microscopy, and x-ray
diffraction. The goal is to identify characteristic properties of the magnetic alteration
products that may help elucidate the relative contributions of microbial and abiotic
alteration mechanisms to the development of an “enhanced” magnetic signature during
pedogenesis. |
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