Reconstructing the Effect of Sulfide Respiration on Global Redox State: Insights from Experiments, Observations, and Models (ReSpires)

To comprehensively reconstruct the evolution of Earth’s climate, atmospheric and seawater chemical compositions, and conditions that favor the proliferation of life, it is critical to constrain all atmospheric carbon dioxide (CO2) and oxygen (O2) sources and sinks—including their dependencies on underlying environmental and geologic drivers. One major CO2 source and O2 sink remains poorly understood: oxidative weathering of sulfide minerals (e.g., pyrite) on land. In addition to driving Earth’s atmospheric composition, pyrite oxidation potentially provides a quantitative proxy for recording past O2 and CO2 levels: the triple-oxygen isotope composition of sulfate. Still, three key questions remain unanswered: (i) what sets the modern-day pyrite oxidation flux, (ii) how has this flux changed over million- to hundred-million-year timescales, and (iii) do geologically preserved sulfate isotopes faithfully record past atmospheric conditions?

Here, I outline a multifaceted research program to answer these questions. This research will develop and apply novel experiments and state-of-the-art geochemical tracers to mechanistically understand pyrite oxidation and resulting sulfate isotope signatures. These results will inform theoretical, kinetic, and numerical models to quantify pyrite oxidation fluxes and atmospheric compositions throughout Earth’s history—this combination of techniques is uniquely afforded by my background and expertise. Specifically, this research will: (i) constrain the electrochemical mechanism of pyrite oxidation and its isotopic consequences, (ii) assess which environmental and geologic controlling factors govern pyrite oxidation rates and fluxes, and (iii) determine how secondary redox cycling in the environment overprints sulfate isotope signatures.