Volatile earliest Triassic sulfur cycle: A consequence of persistent low seawater sulfate concentrations and a high sulfur cycle turnover rate? Martin Schobben a, ⁎, Alan Stebbins b , Thomas J. Algeo c,d , Harald Strauss e , Lucyna Leda a , János Haas f , Ulrich Struck a , Dieter Korn a , Christoph Korte g a Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, D-10115 Berlin, Germany b School for the Environment, University of Massachusetts Boston, 100 Morrissey Blvd., Boston, MA 02125, United States c Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, United States d State Key Laboratories of BGEG and GPMR, China University of Geosciences, Wuhan 430074, China e Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Corrensstraße 24, D-48149 Münster, Germany f MTA-ELTE Geological, Geophysical and Space Science Research Group, Hungarian Academy of Sciences, Pázmány s. 1/c, H-1117 Budapest, Hungary g Department of Geosciences and Natural Resource Management, University of Copenhagen, ØsterVoldgade 10, DK-1350 Copenhagen, Denmark abstract article info Article history: Received 5 September 2016 Received in revised form 21 December 2016 Accepted 17 February 2017 Available online xxxx Marine 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 sul- fate 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 nat- ural 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., Δ 34 S CAS-CRS . We show that, despite region-specific redox conditions, Δ 34 S CAS-CRS exhibits a nearly invariant value of 15–16‰ in both study sections. By comparing our record with a Δ 34 S sulfate-sulfide density distribution for modern marine sediments, we deduce that porewater Rayleigh distillation, carbonate diagenesis, and other effects are unlikely to have appreciably al- tered the S isotope offset between CRS and CAS in the study sections. In addition, differences in sedimentary re- gimes and organic carbon (OC) fluxes between the Iranian and Hungarian sections exclude major influence of the electron donor on MSR-S isotope fractionation and point to a more universal control, i.e., contemporaneous sea- water sulfate concentration. The MSR-trend transfer function yielded estimates of seawater sulfate of 0.6–2.8 mM for the latest Permian to earliest Triassic, suggesting a balanced oceanic S-cycle with equal S inputs and outputs and no major changes in sulfate concentrations during this interval. However, a secular trend toward heavier δ 34 S CAS (by N 5‰) in the earliest Triassic can be explained only by increasing the turnover rate of the S-cycle (by ca. one order of magni- tude) and a concomitant change in terrestrial S sources in a box model experiment. Exposure of evaporite de- posits having a high δ 34 S may account for the source change, with a possible role for the Siberian Traps volcanism by magmatic remobilization of Cambrian rock salt. A high sulfur cycle turnover rate would have left the ocean system vulnerable to development of widespread euxinic conditions, posing a sustained threat to ma- rine life during the Early Triassic. © 2017 Elsevier B.V. All rights reserved. Keywords: Biogeochemical cycles Early diagenesis Carbonate-associated sulfate Sulfur isotopes End-Permian mass extinction Microbial sulfate reduction 1. Introduction The reconstruction of ancient oceanic ion concentrations is critical to an understanding of the evolution of atmospheric oxygen levels (Berner and Canfield, 1989; Canfield et al., 2000), biogeochemical cycles (Strauss, 1999), and biomineralization evolutionary pathways (Stanley Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2017) xxx–xxx ⁎ Corresponding author at: School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, United Kingdom. E-mail address: m.schobben@leeds.ac.uk (M. Schobben). PALAEO-08207; No of Pages 12 http://dx.doi.org/10.1016/j.palaeo.2017.02.025 0031-0182/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo Please cite this article as: Schobben, M., et al., Volatile earliest Triassic sulfur cycle: A consequence of persistent low seawater sulfate concentrations and a high sulfur cycle t..., Palaeogeogr. Palaeoclimatol. Palaeoecol. (2017), http://dx.doi.org/10.1016/j.palaeo.2017.02.025