This study investigates the amount of sulfide sulfur and its sulfur isotopic composition (δ34S) in seep site sediments of the Blake Ridge Diapir (BRD; offshore southeastern United States) and Monterey Bay (offshore California, United States). The geochemistry of these sediments is influenced by anaerobic methane oxidation (AMO). Our aim is to compare the sulfur geochemistry of seeps sites, where advective delivery of methane is an important process, to other localities where AMO is also an important biogeochemical process but where diffusion is the dominant mass transport mechanism. Sulfide sulfur of authigenic sulfide minerals was extracted from sediments using chromium reduction. We measured sulfide sulfur concentration via iodometric titration and in separate runs obtained sulfide precipitate for δ34S analyses. Our concentration measurements are flawed and the δ34S data are pending, so we used data from other studies for our comparisons.
Methane seep sediments of Monterey Bay seem to have significantly higher sulfide content than do those from the BRD, but diffusive and advective sites cannot be distinguished by sulfide sulfur content alone. Data from the literature show that the 34S content of sulfide minerals from seep sites (modal δ34S, ~-30‰ CDT) is intermediate between that of diffusive sediments unaffected by AMO (modal δ34S, ~-35‰) and those affected by AMO (modal δ34S, ~-20‰). However, sulfide sulfur from seep sites and advective sites cannot be distinguished isotopically. Some samples from diffusive sediments located near the present-day sulfate-methane interface show unique sulfide sulfur isotopic compositions with strong 34S enrichment (δ34S > 0‰).
Semester/Year of Award
Walter S. Borowski
Mentor Department Affiliation
Restricted Access Thesis
Department Name when Degree Awarded
Means, V. Lynn, "Concentration and sulfur isotopic composition of authigenic sulfide minerals at methane seep sites versus diffusive sites" (2004). Geosciences Undergraduate Theses. 1.