Sulphidic Mediterranean surface waters during Pliocene sapropel formation

• Published in: Nature (London) Vol. 397; no. 6715; pp. 146 - 149
• Main Authors: Passier, Hilde F, Bosch, Hendrik-Jan, Nijenhuis, Ivar A, Lourens, Lucas J, Böttcher, Michael E, Leenders, Anke, Damsté, Jaap S. Sinninghe, de Lange, Gert J, Leeuw, Jan W
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 14.01.1999; Nature Publishing Group
• Subjects: Bacteria; Climate; Earth sciences; Earth, ocean, space; Exact sciences and technology; Isotope geochemistry; Isotope geochemistry. Geochronology; Marine; Marine geology; Neogene; Oceans; Organic chemistry; Oxygen depletion; Pliocene; Sapropels; Sediments; Sulfur; Surface water; East Mediterranean; Mediterranean Sea; MED, Eastern Mediterranean; Neogene; trace metals; bacteria; upper Tertiary; pyrite; paleo-oceanography; precipitation; photosynthesis; anaerobic environment; sulfur; Cenozoic; Mediterranean Sea; marine sediments; sulfides; stable isotopes; euxinic environment; iron sulfides; sapropel; Tertiary; biomarkers; Pliocene; prokaryotes; organic materials; biogenic effects; Phanerozoic; S-34
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/16441

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 production and increased organic-matter preservation due to oxygen depletion in more stagnant bottom waters,. Here we report that eastern Mediterranean Pliocene sapropels 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.