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| Titel |
Latitudinal differences in the amplitude of the OAE-2 carbon isotopic excursion: pCO2 and paleo productivity |
| VerfasserIn |
E. C. Bentum, G.-J. Reichart, A. Forster, J. S. Sinninghe Damsté |
| 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 ; 9, no. 2 ; Nr. 9, no. 2 (2012-02-09), S.717-731 |
| Datensatznummer |
250006763
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| Publikation (Nr.) |
 copernicus.org/bg-9-717-2012.pdf |
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| Zusammenfassung |
| A complete, well-preserved record of the Cenomanian/Turonian (C/T) Oceanic
Anoxic Event 2 (OAE-2) was recovered from Demerara Rise in the southern
North Atlantic Ocean (ODP site 1260). Across this interval, we determined
changes in the stable carbon isotopic composition of sulfur-bound phytane (δ13Cphytane),
a biomarker for photosynthetic algae. The
δ13Cphytane record shows a positive excursion at the onset
of the OAE-2 interval, with an unusually large amplitude (~7‰)
compared to existing C/T proto-North Atlantic δ13Cphytane
records (3–6‰). Overall, the amplitude of the excursion of δ13Cphytane decreases with latitude.
Using reconstructed sea
surface temperature (SST) gradients for the proto-North Atlantic, we
investigated environmental factors influencing the latitudinal δ13Cphytane gradient.
The observed gradient is best explained by
high productivity at DSDP Site 367 and Tarfaya basin before OAE-2, which
changed in overall high productivity throughout the proto-North Atlantic
during OAE-2. During OAE-2, productivity at site 1260 and 603B was thus more
comparable to the mid-latitude sites. Using these constraints as well as the
SST and δ13Cphytane-records from Site 1260, we
subsequently reconstructed pCO2 levels across the OAE-2 interval.
Accordingly, pCO2 decreased from ca. 1750 to 900 ppm during OAE-2,
consistent with enhanced organic matter burial resulting in lowering
pCO2. Whereas the onset of OAE-2 coincided with increased pCO2, in
line with a volcanic trigger for this event, the observed cooling within
OAE-2 probably resulted from CO2 sequestration in black shales
outcompeting CO2 input into the atmosphere. Together these results show
that the ice-free Cretaceous world was sensitive to changes in pCO2
related to perturbations of the global carbon cycle. |
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