Strong local, not global, controls on marine pyrite sulfur isotopes

Understanding variation in the sulfur isotopic composition of sedimentary pyrite (delta S-34(pyr)) is motivated by the key role of sulfur biogeochemistry in regulating Earth's surface oxidation state. Until recently, the impact of local depositional conditions on delta S-34(pyr) has remained underappreciated, and stratigraphic variations in delta S-34(pyr) were interpreted mostly to reflect global changes in biogeochemical cycling. We present two coeval delta S-34(pyr) records from shelf and basin settings in a single sedimentary system. Despite their proximity and contemporaneous deposition, these two records preserve radically different geochemical signals. Swings of similar to 65 parts per thousand in shelf delta S-34(pyr) track short-term variations in local sedimentation and are completely absent from the abyssal record. In contrast, a long-term similar to 30 parts per thousand decrease in abyssal delta S-34(pyr) reflects regional changes in ocean circulation and/or sustained pyrite formation. These results highlight strong local controls on delta S-34(pyr), calling for reevaluation of the current practice of using delta S-34(pyr) stratigraphic variations to infer global changes in Earth's surface environment.