Volatile earliest Triassic sulfur cycle: A consequence of persistent low seawater sulfate concentrations and a high sulfur cycle turnover rate?

摘要

AbstractMarine biodiversity decreases and ecosystem destruction during the end-Permian mass extinction (EPME) have been linked to widespread marine euxinic conditions. Changes in the biogeochemical sulfur cycle, microbial sulfate reduction (MSR), and marine dissolved sulfate concentrations during the Permian-Triassic transition can provide insights into the role of ocean chemistry change in the largest mass extinction in Earth history. In this study, we constrain marine dissolved sulfate concentrations using the MSR-trend method of Algeo et al. [Algeo, T.J., Luo, G.M., Song, H.Y., Lyons, T.W., Canfield, D.E., 2015. Reconstruction of secular variation in seawater sulfate concentrations. Biogeosciences 12, 2131–2151] on sulfur (S) isotope records from Iran (the Kuh-e-Ali Bashi and Zal sections) and Hungary (the Bálvány North and Bálvány East sections). This empirically derived transfer function is based on the S isotope fractionation between sulfate and sulfide associated with MSR in natural aquatic environments. This fractionation is proxied by the difference in S isotope compositions between chromium-reducible sulfur (CRS) and carbonate-associated sulfate (CAS), i.e., Δ34SCAS-CRS. We show that, despite region-specific redox conditions, Δ34SCAS-CRSexhibits a nearly invariant value of 15–16‰ in both study sections. By comparing our record with a Δ34Ssulfate-sulfidedensity distribution for modern marine sediments, we deduce that porewater Rayleigh distillation, carbonate diagenesis, and other effects are unl