Letter abstract
Nature Geoscience 1, 606 - 610 (2008)
Published online: 17 August 2008 | doi:10.1038/ngeo283
Subject Categories: Biogeochemistry | Palaeoclimate and palaeoceanography
Synchronous basin-wide formation and redox-controlled preservation of a Mediterranean sapropel
Gert J. De Lange1,5, John Thomson2,5, Anja Reitz1,6, Caroline P. Slomp1, M. Speranza Principato3, Elisabetta Erba3 & Cesare Corselli4
Organic-rich sedimentary units called sapropels have formed repeatedly in the eastern Mediterranean Sea, in response to variations of solar radiation. Sapropel formation is due to a change either in the flux of organic matter to the sea floor from productivity changes or in preservation by bottom-water oxygen levels. However, the relative importance of surface-ocean productivity versus deep-water preservation for the formation of these organic-rich shale beds is still being debated, and conflicting interpretations are often invoked1, 2, 3, 4, 5, 6, 7. Here we analyse at high resolution the differences in the composition of the most recent sapropel, S1, in a suite of cores covering the entire eastern Mediterranean basin. We demonstrate that during the 4,000 years of sapropel formation, surface-water salinity was reduced and the deep eastern Mediterranean Sea, below 1,800 m depth, was devoid of oxygen. This resulted in the preferential basin-wide preservation of sapropel S1 with different characteristics above and below 1,800 m depth as a result of different redox conditions. We conclude that climate-induced stratification of the ocean may therefore contribute to enhanced preservation of organic matter in sapropels and potentially also in black shales.
- Department of Earth Sciences—Geochemistry, Faculty of Geosciences, Budapestlaan 4, 3584 CD Utrecht, The Netherlands
- National Oceanography Centre Southampton, Empress Dock, Southampton SO14 3ZH, UK
- Department of Earth Sciences, University of Milano, Via Mangiagalli 34, 20133 Milan, Italy
- Department of Geological Sciences and Geotechnologies, Milano-Bicocca University, Piazza della Scienza 4, 20126 Milan, Italy
- These authors contributed equally to the work
- Present address: Leibniz-Institute Marine Sciences, IFM-GEOMAR, Marine Biogeochemistry, Wischhofstr. 1-3, D-24148 Kiel, Germany
Correspondence to: Gert J. De Lange1,5 e-mail: gdelange@geo.uu.nl
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