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Synchronous basin-wide formation and redox-controlled preservation of a Mediterranean sapropel

Nature Geoscience volume 1, pages 606–610 (2008)Cite this article

Abstract

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.

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Figure 1: Detailed sedimentary profiles for shallow–intermediate–deep-water cores Ap1–SL125–SL114 (811–1,946–3,390 m water depth).
Figure 2: Age (in uncorrected 14C kyr) versus water depth for various distinct boundaries associated with sapropel S1 formation.
Figure 3: Preserved fluxes of calcite, Corg and biogenic Ba, and of the maximum Mn/Al ratio, versus water depth for 14C-dated basin-wide cores.

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Acknowledgements

On-board assistance by ship and scientific teams during cruises with Marion Dufresne (1991, 1995), Tyro (1987, 1991, 1992, 1993), Logachev (1999), Urania (1994, 1997) and Pelagia (2000, 2001, 2004) is acknowledged. We thank M. Paterne, S. Troelstra and the British Ocean Sediment Core Research Facility (BOSCORF) for samples from archive cores; K. van der Borg and A.F.M. de Jong, and the NERC Radiocarbon Laboratory for 14C analyses; and D. Mercone, D. Green, G. Nobbe, H. de Waard, G. Peters, D. van der Meent, R. Knoop, S. Gusic, P. Knutz, C. de Ioanna and E. Schefuss for analytical assistance. This work was supported by European (SAP) and national scientific organizations (Pass2, Saps)

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Author notes

  1. Anja Reitz

    Present address: Present address: Leibniz-Institute Marine Sciences, IFM-GEOMAR, Marine Biogeochemistry, Wischhofstr. 1-3, D-24148 Kiel, Germany,

  2. Gert J. De Lange and John Thomson: These authors contributed equally to the work

Authors and Affiliations

  1. Department of Earth Sciences—Geochemistry, Faculty of Geosciences, Budapestlaan 4, 3584 CD Utrecht, The Netherlands

    Gert J. De Lange, Anja Reitz & Caroline P. Slomp

  2. National Oceanography Centre Southampton, Empress Dock, Southampton SO14 3ZH, UK

    John Thomson

  3. Department of Earth Sciences, University of Milano, Via Mangiagalli 34, 20133 Milan, Italy

    M. Speranza Principato & Elisabetta Erba

  4. Department of Geological Sciences and Geotechnologies, Milano-Bicocca University, Piazza della Scienza 4, 20126 Milan, Italy

    Cesare Corselli

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  1. Gert J. De Lange
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Contributions

G.J.D.L. and J.T. were responsible for geochemical results and interpretation; A.R. and C.P.S. contributed to geochemical results; M.S.P., E.E. and C.C. were responsible for micropalaeontological results. All authors agree to all of the content in the manuscript including the data as presented

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Correspondence to Gert J. De Lange.

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De Lange, G., Thomson, J., Reitz, A. et al. Synchronous basin-wide formation and redox-controlled preservation of a Mediterranean sapropel. Nature Geosci 1, 606–610 (2008). https://doi.org/10.1038/ngeo283

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