Global enhancement of ocean anoxia during oceanic anoxic event 2

A quantitative approach using U isotopes

verfasst von

Carolina Montoya-Pino, Stefan Weyer, Ariel D. Anbar, Jörg Pross, Wolfgang Oschmann, Bas van de Schootbrugge, Helge W. Arz

Abstract

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 ²³⁸U/²³⁵U isotope ratio (δ²³⁸U), 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 δ²³⁸U 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.

Externe Organisation(en)

Goethe-Universität Frankfurt am Main
Arizona State University
Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum (GFZ)
Universität zu Köln

Typ

Artikel

Journal

GEOLOGY

Band

38

Seiten

315-318

Anzahl der Seiten

4

ISSN

0091-7613

Publikationsdatum

04.2010

Publikationsstatus

Veröffentlicht

Peer-reviewed

Ja

ASJC Scopus Sachgebiete

Geologie

Ziele für nachhaltige Entwicklung

SDG 14 – Lebensraum Wasser

Elektronische Version(en)

https://doi.org/10.1130/G30652.1 (Zugang: Unbekannt)