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| Titel |
Perturbations to the Global Sulfur Cycle during a mid-Cretaceous Oceanic Anoxic Event (OAE 2: Cenomanian/Turonian) |
| VerfasserIn |
J. D. Owens, B. C. Gill, H. Jenkyns, M. M. M. Kuypers, S. Severmann, S. Bates, T. W. Lyons |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250070853
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| Zusammenfassung |
| Understanding the causes and consequences of oceanic anoxic events (OAEs) has been at the
forefront of studies of paleoceanography for the last several decades. This interest stems in
large part from the biological and biogeochemical impacts of these events, with possible
parallels to recent expansion of coastal hypoxia and broader deoxygenation in the modern
ocean. The Mesozoic Era is noted for numerous OAEs that are diagnostically expressed by
widespread organic-carbon deposition and coeval positive carbon-isotope excursions. Recent
work on Jurassic and Cretaceous OAEs has shown that, coupled with the overall
increase in carbon-isotope values, are parallel positive sulfur-isotope excursions in
carbonate-associated sulfur (CAS)—a proxy that can faithfully record the isotopic
composition of seawater sulfate. The parallel positive carbon and sulfur isotope
excursions of OAE 2 (~93.5 Ma) suggest the large-scale, coupled burial of organic
carbon and pyrite sulfur, although the peaks of the these shifts are offset by a few
hundred thousand years. The sulfate isotope curve for OAE 2 recovered to pre-event
levels in ~4 Ma. This observation, coupled with our preliminary modeling results,
suggests that sulfate concentrations were between 5 and 7 mM compared to 28 mM
present today. We have used biogeochemical box modeling to explore the factors
behind the perturbations of the C–S cycles. In order to replicate the isotopic offset
between the C and S data, the model demands that euxinic burial of pyrite must have
continued a few hundred thousand years after the peak organic-carbon burial. Also,
increasing ΔS — the difference between the isotopic composition of marine sulfate and
pyrite formed from that sulfate —substantially lessens the required increase in
pyrite burial needed to drive the sulfur-isotope excursion. Such a mechanism is
likely, given the expansion of euxinia and the attendant increase in pyrite formation
in the water column. Quantitative consideration of these cycles is of paramount
importance for constraining the budgets of carbon and sulfur, but also oxygen and other
elements, as we seek to improve our understanding of the mechanisms behind OAEs. |
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