Temporal variations of sedimentary sulfur in a Delaware salt marsh

Abstract

The cycling of sedimentary sulfur was examined over a one year period in the Great Marsh, Delaware (U.S.A.) using newly developed analytical procedures. Iron monosulfide (FeS) and elemental sulfur both display large seasonal changes in concentration and distribution with depth, indicating a coupling with marsh redox conditions. In contrast, the depth distribution and concentration of greigite (Fe 3S 4) did not show appreciable changes with season. Pyrite (FeS 2) underwent large concentration changes in the upper 15 cm of sediment during the spring, but remained relatively constant with respect to concentration and distribution below this zone. Using a mass balance approach in the upper marsh sediment, sulfur needed for rapid pyritization is found to be derived from elemental sulfur, iron monosulfide and sulfate reduction. In the deeper sediments, pyritization occurs through a greigite intermediate, and diagenetic modeling indicates that pyrite formation is limited by the synthesis of greigite, and not by the conversion of greigite to pyrite.