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| Titel |
Ocean anoxia did not cause the Latest Permian Extinction |
| VerfasserIn |
Bernadette C. Proemse, Stephen E. Grasby, Michael E. Wieser, Bernhard Mayer, Benoit Beauchamp |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093906
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| Publikation (Nr.) |
 EGU/EGU2014-9089.pdf |
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| Zusammenfassung |
| The Latest Permian Extinction (LPE, ~252 million years ago) was a turning point in the
history of life on Earth with a loss of ~96% of all marine species and ~70% of all
terrestrial species. While, the event undoubtedly shaped the evolution of life its cause
remains enigmatic. A leading hypothesis is that the global oceans became depleted in
oxygen (anoxia). In order to test this hypothesis we investigated a proxy for marine
oxygen levels (molybdenum isotopic composition) in shale across the LPE horizon
located on the subtropical northwest margin of Pangea at that time. We studied
two sedimentary records in the Sverdrup basin, Canadian High Arctic: Buchanan
Lake (eastern Axel Heiberg Island; 79°26.1´N, 87°12.6´W), representing a distal
deep-water slope environment, and West Blind Fiord (southwest Ellesmere Island; 78Ë
23.9´N, 85°57.2´W), representing a deep outer shelf environment (below storm wave
base).
The molybdenum isotopic composition (δ98-95Mo) of sediments has recently
become a powerful tool as a paleo-oceanographic proxy of marine oxygen levels.
Sample preparation was carried out in a metal-free clean room facility in the isotope
laboratory of the Department of Physics and Astronomy, University of Calgary,
Canada, that is supplied by HEPA-filtered air. Molybdenum isotope ratios were
determined on a Thermo Scientific multi-collector inductively coupled plasma mass
spectrometer (MC-ICP-MS) with an uncertainty better than ±0.10ofor δ98-95Mo
values.
Results from the Buchanan Lake section show a large shift in δ98-95Mo values
from 2.02oto +2.23oat the extinction horizon, consistent with onset of euxinic
conditions. In contrast, West Blind Fiord shales, representing the sub-storm wave base
shelf environment, show little change in the molybdenum isotopic composition
(1.34oto +0.05), indicating ongoing oxic conditions across the LPE (Proemse et al.,
2013).
Our results suggest that areas of the Pangea continental shelf (North West Pangea)
experienced oxic conditions throughout the LPE event, while anoxic conditions developed in
the deep ocean. Hence, anoxic marine waters did not extend globally onto shelf environments
and as such ocean anoxia cannot have been the main driver of the extinction event. While
global systems were stressed by anoxia, the anoxic conditions may better represent a
symptom of Siberian Trap eruptions that had catastrophic impact on the environment,
potentially through nutrient loading and deposition of toxic substances into marine and
terrestrial systems.
Proemse et al., 2013: Molybdenum isotopic evidence for oxic marine conditions during
the latest Permian extinction. Geology 41, 967-970. |
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