Global enhancement of ocean anoxia during Oceanic Anoxic Event 2: A quantitative approach using U isotopes
| Autor: | Helge W Arz, Stefan Weyer, Ariel D. Anbar, Jörg Pross, Carolina Montoya-Pino, Wolfgang Oschmann, Bas van de Schootbrugge |
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| Přispěvatelé: | 5.2 Climate Dynamics and Landscape Evolution, 5.0 Earth Surface Processes, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum |
| Rok vydání: | 2010 |
| Předmět: | |
| Zdroj: | Geology |
| ISSN: | 1943-2682 0091-7613 |
| Popis: | During the Mesozoic greenhouse world, the oceans underwent several oceanic anoxic events (OAEs) characterized by intervals during which organic-rich black shales were deposited, indicating strong oxygen depletion in the marine realm. The Cenomanian-Turonian OAE2 (ca. 93 Ma) represents one of the most prominent events of the Cretaceous, with significant perturbations of the global carbon cycle. Although OAE2 likely reached a global scale, the spatial extent of seawater anoxia during this OAE is poorly constrained. Here we demonstrate that variations in the U-238/U-235 isotope ratio (delta U-238), a newly developed paleoredox proxy, can be used to quantify the extent of marine anoxia. For black shales from the mid-Cretaceous OAE2 we find a systematic shift toward lighter delta U-238 and lower U concentrations as compared to modern equivalent organic-rich sediments from the Black Sea. This shift translates to a global increase of oceanic anoxia during OAE2 by at least a factor of three as compared to the present day or to periods before and after OAE2. The constant offset in U concentrations and isotope compositions of black shales throughout OAE2 compared to modern Black Sea sediments indicates an enhancement of oceanic anoxic conditions already prior to the onset of OAE2. |
| Databáze: | OpenAIRE |
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