Sedimentary pyrite sulfur isotopes track the local dynamics of the Peruvian oxygen minimum zone.

ABSTRACT: Sulfur cycling is ubiquitous in sedimentary environments, where it mediates organic carbon remineralization, impacting both local and global redox budgets, and leaving an imprint in pyrite sulfur isotope ratios (δ³⁴S_pyr). It is unclear to what extent stratigraphic δ³⁴S_pyr variations reflect local aspects of the depositional environment or microbial activity versus global sulfur-cycle variations. Here, we couple carbon-nitrogen-sulfur concentrations and stable isotopes to identify clear influences on δ³⁴S_pyr of local environmental changes along the Peru margin. Stratigraphically coherent glacial-interglacial δ³⁴S_pyr fluctuations (>30‰) were mediated by Oxygen Minimum Zone intensification/expansion and local enhancement of organic matter deposition. The higher resulting microbial sulfate reduction rates led to more effective drawdown and ³⁴S-enrichment of residual porewater sulfate and sulfide produced from it, some of which is preserved in pyrite. We identify organic carbon loading as a major influence on δ³⁴S_pyr, adding to the growing body of evidence highlighting the local controls on these records.

SUBMITTER: Pasquier V 

PROVIDER: S-EPMC8292381 | biostudies-literature | 2021 Jul

REPOSITORIES: biostudies-literature