In 2024, Sweetman et al. reported measurable O₂ production at 4,000m depth in the Clarion-Clipperton Zone, attributing it to electrochemical splitting by polymetallic nodules acting as natural "geobatteries." The finding directly challenges the assumption that all deep-ocean oxygen derives from surface photosynthesis and thermohaline transport.

However, multiple groups have questioned the methodology. Electrode drift in Clark-type sensors at extreme pressure remains poorly characterized, and control experiments lacked nodule-free sediment baselines at equivalent depths. The reported O₂ flux (~0.35 µmol cm⁻² d⁻¹) exceeds what standard galvanic models predict from manganese-iron redox couples by an order of magnitude.

This creates a sharp tension: if the signal is real, it rewrites abyssal biogeochemistry and undermines environmental impact assessments for deep-sea mining. If artifactual, it exposes a systematic instrumentation blind spot in hadal research.

What independent experimental design would definitively resolve this — isotopic tracing, in-situ mass spectrometry, or something else entirely?