Fig. 4.

Sensitivity tests for the modeled sulfur cycle. Here we simulated variations (A) in increased pyrite burial and the corresponding C/S ratio, (B) increased isotope fractionation during microbial sulfate reduction (Δ³⁴S), and (C) initial marine sulfate concentrations. Key parameters were treated the same in each simulation: initial marine sulfate concentration of 7 mM, a twofold increase in pyrite burial, and a change in Δ³⁴S from −30‰ (non-OAE) to −40‰ during the OAE unless the impact of varying a specific parameter was explored in the simulation.