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| Titel |
Reconstruction of secular variation in seawater sulfate concentrations |
| VerfasserIn |
T. J. Algeo, G. M. Luo, H. Y. Song, T. W. Lyons, D. E. Canfield |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 7 ; Nr. 12, no. 7 (2015-04-10), S.2131-2151 |
| Datensatznummer |
250117892
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| Publikation (Nr.) |
 copernicus.org/bg-12-2131-2015.pdf |
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| Zusammenfassung |
| Long-term secular
variation in seawater sulfate concentrations ([SO42−]SW) is
of interest owing to its relationship to the oxygenation history of Earth's
surface environment. In this study, we develop two complementary approaches
for quantification of sulfate concentrations in ancient seawater and test
their application to late Neoproterozoic (635 Ma) to Recent marine units.
The "rate method" is based on two measurable parameters of paleomarine
systems: (1) the S-isotope fractionation associated with microbial sulfate
reduction (MSR), as proxied by Δ34SCAS-PY, and (2) the
maximum rate of change in seawater sulfate, as proxied by &partial; δ
34SCAS/∂ t(max). The "MSR-trend method" is
based on the empirical relationship of Δ34SCAS-PY to
aqueous sulfate concentrations in 81 modern depositional systems. For a given
paleomarine system, the rate method yields an estimate of maximum possible
[SO42−]SW (although results are dependent on assumptions
regarding the pyrite burial flux, FPY), and the MSR-trend method
yields an estimate of mean [SO42−]SW. An analysis of
seawater sulfate concentrations since 635 Ma suggests that
[SO42−]SW was low during the late Neoproterozoic (<5 mM), rose sharply across the Ediacaran–Cambrian boundary (~5–10 mM),
and rose again during the Permian (~10–30 mM) to levels that have
varied only slightly since 250 Ma. However, Phanerozoic seawater sulfate
concentrations may have been drawn down to much lower levels
(~1–4 mM) during short (<~2 Myr) intervals of the
Cambrian, Early Triassic, Early Jurassic, and Cretaceous as a consequence of
widespread ocean anoxia, intense MSR, and pyrite burial. The procedures
developed in this study offer potential for future high-resolution
quantitative analyses of paleo-seawater sulfate concentrations. |
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