The cycling of particulate carbon, nitrogen, sulfur, and sulfur species (iron monosulfide, greigite, pyrite, and organic sulfur) in the water columns of Framvaren Fjord and the Black Sea

• Published in: Marine chemistry 1999-11, Vol.67 (3), p.149-160
• Main Authors: Cutter, Gregory A, Kluckhohn, Robert S
• Format: Article
• Language: English
• Subjects: anoxic water column; Black Sea; Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Framvaren Fjord; Geochemistry; Marine; Mineralogy; organic sulfur; Physical and chemical properties of sea water; Physics of the oceans; pyrite; Silicates; suspended particles; Water geochemistry
• ISSN: 0304-4203; 1872-7581
• DOI: 10.1016/S0304-4203(99)00056-0

Particulate organic carbon, nitrogen, and sulfur are produced in surface waters from photosynthesis and regenerated via oxic respiration. When this organic matter reaches anoxic marine environments, regeneration is largely coupled with sulfate reduction. Hydrogen sulfide from microbial sulfate reduction reacts with Fe(II) through various mechanisms to produce several iron sulfides, of which pyrite (FeS 2) is the most stable in marine sediments. As such, sedimentary pyrite may serve as a long term indicator of conditions under which it was formed. In this respect it has been argued that pyrite can be formed in the anoxic water column as well as produced in the underlying sediments, thus affecting any paleoceanographic interpretations using pyrite and other tracers. Despite this important possibility, few direct observations of pyrite formation in the anoxic water column have been reported. Using analytical methods that are capable of detecting nanomolar concentrations of iron sulfides in suspended particles, depth profiles were obtained for iron monosulfide (FeS), greigite (Fe 3S 4), and pyrite in the anoxic water columns of Framvaren Fjord and the Black Sea; profiles of particulate C, N, and S were also acquired. In Framvaren, maximum particulate C and N were found at the oxic/anoxic interface, while the highest concentrations of particulate organic S (POS) were just above this interface. This low C/N organic matter probably lead to the high concentrations of hydrogen sulfide observed in the deeper waters of Framvaren. Pyrite and greigite showed concentration maxima just below the oxic/anoxic interface, while FeS was almost non-detectable. Throughout the anoxic water column, these iron sulfides comprised 73% of the total particulate sulfur, and filtration experiments indicate that much of the iron sulfide particles were