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Sulphidic Mediterranean surface waters during Pliocene sapropel formation


Sapropels—organic-matter rich layers—are common in Neogene sediments of the eastern Mediterranean Sea. The formation of these layers has been attributed to climate-related increases in organic-matter production1,2,3 and increased organic-matter preservation due to oxygen depletion in more stagnant bottom waters2,3. Here we report that eastern Mediterranean Pliocene sapropels4 contain molecular fossils of a compound (isorenieratene) known to be synthesized by photosynthetic green sulphur bacteria, suggesting that sulphidic (euxinic)—and therefore anoxic—conditions prevailed in the photic zone of the water column. These sapropels also have a high trace-metal content, which is probably due to the efficient scavenging of these metals by precipitating sulphides in a euxinic water column. The abundance and sulphur-isotope composition of pyrite are consistent with iron sulphide formation in the water column. We conclude that basin-wide water-column euxinia occurred over substantial periods during Pliocene sapropel formation in the eastern Mediterranean Sea, and that the ultimate degradation of the increased organic-matter production was strongly influential in generating and sustaining the euxinic conditions.

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Figure 1
Figure 2: Sapropel compositional data.


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We thank S. McNab for linguistic advice; G. Nobbe, H. de Waard and T. Zalm for analytical assistance; and The Ocean Drilling Program and Leg 160 shipboard participants for their co-operation. This is a publication of the Netherlands Research School of Sedimentary Geology. This work was supported in part by the Netherlands Organization for Scientific Research (NWO) and the European Union Marine Science and Technology (MAST) programme.

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Correspondence to Hilde F. Passier.

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Passier, H., Bosch, HJ., Nijenhuis, I. et al. Sulphidic Mediterranean surface waters during Pliocene sapropel formation. Nature 397, 146–149 (1999).

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