Hydroclimate controls Congo peatland net oxygen release over the past 10,600 years.

The burial of organic matter in marine environments is considered the dominant long-term source of atmospheric oxygen, yet the contribution of terrestrial burial remains poorly constrained. Quantifying any oxygen surplus associated with organic matter burial conventionally assumes a 1:1 oxygen-to-carbon stoichiometry. Here we aim to test this assumption and quantify net oxygen release from a terrestrial setting over time. We applied direct redox titration to a 10,600-year Congo Basin peat core, a hotspot of carbon accumulation. We find systematic deviation from the 1:1 ratio, enabling precise, time-resolved quantification of the net redox imbalance. Fluxes were strikingly nonlinear: drier phases triggered abrupt ~80% declines in net oxygen surplus within centuries, followed by rapid recovery when wetter conditions returned, revealing a hydroclimate-sensitive carbon-oxygen valve. Cumulative Holocene oxygen surplus reached 83 [68-100] petagrams of oxygen equivalents. Using the Congo oxygen-to-carbon ratio, we estimate that global peatland net oxygen production is commensurate with continental weathering oxygen sinks in the Holocene-a flux comparable in magnitude to marine burial but responding on orders-of-magnitude-shorter timescales. This finding provides qualitative insight into the contribution of terrestrial environments to Earth's redox balance. It also offers a direct stoichiometric framework-applicable to coal archives-for quantifying that contribution across the Phanerozoic, independent of isotopic proxies, complementing existing marine-based models.