Quantifying pyrite oxidation on continental shelves during the onset of Antarctic glaciation in the Eocene-Oligocene transition

The Eocene-Oligocene transition (EOT) is characterized by a global cooling trend, falling sea levels, and the onset of Antarctic glaciation. Previous studies investigate the interactions and feedbacks between ocean circulation, weathering, and atmospheric CO₂ levels during this time. Here we explore the role of biogeochemical sulfur cycling, and report seawater sulfate isotope data across the EOT. Our data show that seawater sulfate δ³⁴S and δ¹⁸O_SO4 values decline by 0.6‰ and 1.5‰, respectively, between 34.5 and 33 Ma. Quantitative modeling suggests that approximately 8,000 Gt of the sulfide previously stored in shelf sediments has been reoxidized and transferred to the marine sulfate pool. This reoxidation process proceeds through reactions similar to those associated with acid mine drainage, generating 24,500 Gt sulfuric acid. These numbers are of similar magnitude as those estimated for Pleistocene glaciations and must have affected marine pH and/or alkalinity.