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Titel |
Early diagenesis of trace metals (V, Mo, U) in sediments of the Peruvian upwelling area: response to oxygen dynamics in the water column |
VerfasserIn |
Florian Scholz, Christian Hensen, Anna Noffke, Anne Rhode, Klaus Wallmann |
Konferenz |
EGU General Assembly 2011
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 13 (2011) |
Datensatznummer |
250055073
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Zusammenfassung |
The upwelling area in the eastern equatorial Pacific off Peru is one of the most pronounced
oxygen minimum zones (OMZs) of the modern ocean. Modeling scenarios predict an
expansion of the OMZs in the course of global change in the coming decades. As a
consequence, the Peruvian continental margin represents a key locality for studies on
biogeochemical dynamics in the future ocean.
We present pore water and sediment data for redox-sensitive metals (Fe, Mn, V, Mo, and
U) that have been collected along a transect across the Peruvian margin at 11Ë S. The results
are used to evaluate the behavior of trace metals in a wide range of biogeochemical and
hydrodynamic settings.
In the core of the OMZ, where permanently anoxic conditions prevail, redox
sensitive metals exhibit diagenetic behaviors largely consistent with previous studies.
Vanadium and Mo are released from Fe oxihydroxides and subsequently recycled
through diffusion across the benthic boundary or trapped through formation of
authigenic V phases and sequestration of Mo by authigenic pyrite. Some U is delivered
through diffusion across the benthic boundary, reduction and precipitation of UO2 and
incorporation into phosphorites. The utmost part of the buried U, however, is delivered in
particulate form, most likely as bioauthigenic U which cannot be recycled in the suboxic
waters overlying the anoxic sediments. In contrast to sediments in the core of the
OMZ, sediments on the shelf experience frequent oxygenation episodes related to
the passage of internal waves and the regular recurrence of El Niño events. These
oxygenation episodes lead to the re-oxidation and remobilization of authigenic U and V. In
contrast to that, the authigenic accumulation of Mo is favored by the occasional
occurrence of slightly oxidizing conditions. This is most likely due to enhanced
formation of sulfur intermediates necessary for pyrite formation and the increased
stability of pyrite, the major Mo sink, under oxidizing conditions, compared to
authigenic V and U phases. Redox oscillations in the Peruvian OMZ thus lead to a
discrimination of U against Mo, a mechanism that should be considered in the interpretation
of U/Mo systematics in paleo redox studies. Overall our results provide valuable
constraints on how trace metal inventories of marginal sediments may respond to
expanding shelf anoxia and to short term perturbations of sediment redox conditions. |
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