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Lookup NU author(s): Professor Simon Poulton
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The photosynthetic production of oxygen in the oceans is thought to have begun by 2.7 billion years ago, several hundred million years before appreciable accumulation of oxygen in the atmosphere. However, the abundance and distribution of dissolved oxygen in the late Archaean oceans is poorly constrained. Here we present geochemical profiles from 2.6- to 2.5-billion-year-old black shales from the Campbellrand-Malmani carbonate platform in South Africa. We find a high abundance of rhenium and a low abundance of molybdenum, which, together with the speciation of sedimentary iron, points to the presence of dissolved oxygen in the bottom waters on the platform slope. The water depth on the slope probably reached several hundred metres, implying the export of O-2 below the photic zone. Our data also indicate that the mildly oxygenated surface ocean gave way to an anoxic deep ocean. We therefore suggest that the production of oxygen in the surface ocean was vigorous at this time, but was not sufficient to fully consume the deep-sea reductants. On the basis of our results and observations from the Hamersley basin in Western Australia, we conclude that the productive regions along ocean margins during the late Archaean eon were sites of substantial O-2 accumulation, at least 100 million years before the first significant increase in atmospheric O-2 concentration.
Author(s): Kendall B, Reinhard CT, Lyons T, Kaufman AJ, Poulton S, Anbar AD
Publication type: Article
Publication status: Published
Journal: Nature Geoscience
Year: 2010
Volume: 3
Issue: 9
Pages: 647-652
Print publication date: 01/09/2010
ISSN (print): 1752-0894
ISSN (electronic): 1752-0908
Publisher: Nature Publishing Group
URL: http://dx.doi.org/10.1038/NGEO942
DOI: 10.1038/NGEO942
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