Early diagenesis of sulfur in Bornholm Basin sediments: The role of upward diffusion of isotopically “heavy” sulfide

Sediment-hosted marine sulfur cycling has played a significant role in regulating Earth’s surface chemistry over our planet’s history. Microbially-mediated reactions involving are often accompanied by isotope fractionation that, turn, is captured sulfate and sulfide minerals, providing the opportunity to track changes microbial utilization of thus cycle. Studying diagenesis within Bornholm Basin, Baltic Sea, we explore interplay between carbon, iron, focusing on fate dynamics oxygen isotopic response as function varying thickness organic carbon-rich Holocene Mud Layer (HML) across basin. Using one-dimensional reaction-transport model, porewater profiles were used calculate net reduction rates (SRR) production rates, respectively. These calculations suggest positive relationship HML production. Given that ascending enriched 34S relative produced in-situ, heightened flux promotes spatially variable precipitation 34S-enriched pyrite (δ34S ≈ −10‰) close sediment–water interface. Modeling results indicate this isotopically “heavy” formed consequence mixing (up +6.3‰) in-situ (ca. −40‰). Further, show composition controlled SRR: when SRR high (i.e., sulfide-replete settings) downcore increase δ18OSO4 dampened δ34SSO4, whereas low iron-rich parts basin) values while δ34SSO4 remain invariant. We conclude sedimentation open system diffusion strongly influence distribution species their composition, well sulfate, through interaction methane. This work highlights importance considering better understand δ34S signatures both modern settings ancient rocks.