Methods:Total acid digestion:• Dissolution of dry sediment in 3 mL HCl, 2 mL HNO3, and 0.5 mL HF in a CEM Mars Xpress microwave system• Elemental contents determined by ICP-OES (Iris Intrepid II)Sequential Fe extraction:• after Poulton and Canfield (2005) and Henkel et al. (2016)δ56Fe analysis:• Processing after Henkel et al. (2016)• Column separation after Schoenberg and von Blanckenburg (2005)• Isotope analysis on a ThermoFinnigan Neptune Multicollector-ICP-MS (standard-sample bracketing method with IRMM-014) (Schoenberg and von Blanckenburg 2005)Acid volatile sulfur (AVS):• Extraction with 6M HCl (e.g., Cornwell and Morse 1987)Chromium reducible sulfur (CRS):• Extraction with CrCl2 solution (e.g., Zhabina and Volkov 1978, Canfield et al. 1986)