Pulses of ocean acidification at the Triassic-Jurassic boundary

Mass extinctions have repeatedly perturbed the history of life, but their causes are often elusive. Ocean acidification has been implicated during Triassic-Jurassic environmental perturbations, but this interval lacks direct reconstructions of ocean pH. Here, we present boron isotope data from well-preserved fossil oysters, which provide evidence for acidification of ≥ 0.29 pH units coincident with a 2 ‰ negative carbon isotope excursion (the "main" CIE) following the end-Triassic extinction. These results suggest a prolonged interval of CO₂-driven environmental perturbation that may have delayed ecosystem recovery. Earth system modelling with cGENIE paired with our pH constraints demonstrates this was driven by predominantly mantle-derived carbon. Ocean acidification therefore appears to be associated with three of the five largest extinction events in Earth history, highlighting the catastrophic ecological impact of major perturbations to the carbon cycle in Earth's past, and possibly Earth's anthropogenically perturbed future.