Isotopically “heavy” pyrite in marine sediments due to high sedimentation rates and non-steady-state deposition

Abstract Sedimentary pyrite formation links the global biogeochemical cycles of carbon, sulfur, and iron, which, in turn, modulate redox state planet's surficial environment over geological time scales. Accordingly, sulfur isotopic composition (δ34S) has been widely employed as a geochemical tool to probe evolution ocean chemistry. Characteristics depositional post-depositional processes, however, can modify δ34S signal that is captured sedimentary ultimately preserved record. Exploring iron diagenesis within Bornholm Basin, Baltic Sea, we find higher sedimentation rates limit near-surface sulfidization reactive facilitating its burial hence subsurface availability for continued progressively more 34S-enriched sediment-hosted (δ34S ≈ −5‰). Using diagenetic model, show amount formed at sediment-water interface increased past few centuries response expansion water-column hypoxia, which also impacts signature depth. This contribution highlights critical role questions what degree values truly reflect chemistry processes. work strengthens our ability extract local paleoenvironmental information from signatures.