<p>Pyrite formation and burial in anoxic ocean environments helps to regulate the acid–base balance of the oceans. Despite its potential importance, the impact of this anoxic alkalinity production on the global carbon cycle and Earth’s long-term climate regulation has been largely overlooked. Here, using a coupled carbon–sulfur cycle model, we show that pyrite burial could drive 5–46 Tmol yr⁻¹ of alkalinity production—up to about six times the modern background volcanic carbon flux—throughout the Phanerozoic eon. During periods of widespread oceanic anoxia (known as oceanic anoxic events), alkalinity production via pyrite burial is amplified and so becomes an important stabilizing mechanism for the climate system, counterbalancing carbon emissions from contemporaneous large igneous province volcanism. Our results indicate that the anoxia–alkalinity feedback was engaged during several of the most severe oceanic anoxic events from large igneous provinces during the past 300 Myr, and thus played a role in limiting the overall impacts of these events on the biosphere and climate. We conclude that ocean deoxygenation may provide an important negative feedback on ocean–atmosphere CO₂ partitioning, helping to buffer the impacts of CO₂ emission on the Earth system.</p>