Microbial sulfate reduction in deep sediments of the Southwest Pacific (ODP Leg 181, Sites 1119–1125): evidence from stable sulfur isotope fractionation and pore water modeling

• Published in: Marine geology Vol. 205; no. 1; pp. 249 - 260
• Main Authors: Böttcher, Michael E., Khim, Boo-Keun, Suzuki, Atsushi, Gehre, Matthias, Wortmann, Ulrich G., Brumsack, Hans-J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30.04.2004
• Subjects: dissolved sulfate; microbial sulfate reduction; Ocean Drilling Program; pore water modeling; pyrite; Southwest Pacific; stable sulfur isotopes; PSW, South Pacific, Rekohu Drift, ODP Site 1124, Leg 181; PSW, South Pacific, North Chatham Slope, ODP Site 1125, Leg 181; PSE, South Pacific, Canterbury Basin, Site 1119, Leg 181; PSW, South Pacific, Chatham Rise, North Chatham Drift, ODP Site 1123, Leg 181; PSW, South Pacific, Bounty Trough, Bounty Fan, ODP Site 1122, Leg 181; PSE, South Pacific, Campbell Drift, Site 1121, Leg 181; PSE, South Pacific, Campbell Plateau, Site 1120, Leg 181; Southwest Pacific; microbial sulfate reduction; dissolved sulfate; stable sulfur isotopes; Ocean Drilling Program; pyrite; pore water modeling
• ISSN: 0025-3227; 1872-6151
• DOI: 10.1016/S0025-3227(04)00026-X

Interstitial water samples from seven ODP sites (Leg 181, Sites 1119–1125) of the southwestern Pacific Ocean have been analyzed for the stable sulfur isotopic composition of dissolved sulfate along with major and minor ions. Sulfate from the interstitial fluids (δ 34S values between +20.7 and +60‰ vs. the SO 2-based Vienna–Canyon Diablo troilite standard) was enriched in 34S with respect to modern sea water (δ 34S≈+20.6‰) indicating that microbial sulfate reduction takes place to different extents at all investigated sites. Microbial sulfate reduction (MSR) was found at all sites, the intensity depending on the availability of organic matter which is controlled by paleo-sedimentation conditions (sedimentation rate, presence of turbidites) and productivity. Microbial net sulfate reduction was additionally confirmed by modeling interstitial water sulfate profiles. Areal net sulfate reduction rates up to 14 mmol m −2 yr −1 have been calculated which were positively related to sedimentation rates. Total reduced inorganic sulfur (TRIS; essentially pyrite) as a product of microbial sulfate reduction was isotopically characterized in squeeze cake samples and gave δ 34S values between −51 and +9‰ indicating pyrite formation both close to the sediment–water interface and later diagenetic contributions.