Anomalous accumulation of acid-volatile sulphides (AVS) in a coastal marine sediment, Saguenay Fjord, Canada

Details Anomalous accumulation of acid-volatile sulphides (AVS) in a coastal marine sediment, Saguenay Fjord, Canada Anomalous accumulation of acid-volatile sulphides (AVS) in a coastal marine sediment, Saguenay Fjord, Canada

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59.2663g&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 59, Issue 13, pp.2663-2675

Computer Science

4

Scientific paper

Sulphate reduction usually leads to the formation and accumulation of authigenic pyrite (FeS 2 ) in organic-rich coastal marine sediments. Iron monosulphides (FeS x ) are most often found as a minor constituent of the reduced sulphur pool in these sediments and are believed to be precursor phases which convert to pyrite during early diagenesis. Abnormally high ratios of acid-volatile sulphides (AVS) to pyrite, however, are found in the sediments of the Saguenay Fjord, Canada. The AVS-S:FeS 2 ---S ratio observed throughout the anoxic zone in three sediment cores collected along the main axis of the fjord generally exceeds 1 and reaches values as high as 7 at the head of the fjord. To document and explain this anomaly, solid phase components (AVS, FeS 2 , S 0 , reactive iron (Fe HCl ), C ORG , and total N) as well as porewater constituents (SO 4 , Fe, and Mn) were analyzed. Degree of pyritization (DOP) values were low (0.1-11%) and generally decreased toward the mouth of the fjord. In contrast, degree of sulphidization (DOS) estimates were high and reached values of up to 43% at the head of the fjord. These latter values indicate that pyrite formation is not limited by iron availability but a large excess of reactive iron may in fact inhibit the build-up of reduced sulphur ( H 2 S) in the porewaters as a result of AVS-S precipitation. In the absence of a strong H 2 S gradient, slow diffusion to the redox boundary and limited formation of soluble intermediate reduced sulphur species may hinder the conversion of AVS to pyrite.

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