Oxygen found in deep ocean darkness

Researchers have detected oxygen production at depths of 4,000 meters in the Clarion-Clipperton zone of the Pacific Ocean, a region where sunlight and living organisms are absent. This unexpected oxygen generation has raised questions about the mechanisms behind it.

Geobatteries on the ocean floor

The oxygen is believed to originate from polymetallic nodules on the ocean floor, which act as natural geobatteries. These nodules can generate up to 0.95 volts when in contact with seawater, potentially triggering chemical reactions that produce oxygen.

Controversy over the findings

The discovery, published in the journal Nature Geoscience in 2024, has sparked debate. The Metals Company, which partially funds the study, has called the research defective, and a 2025 opinion article in Frontiers in Marine Science disputes the oxygen production rates.

Historical context and confirmation

The study was first noted in 2013, but initial signals were attributed to faulty sensors. A second independent measurement in 2021 confirmed the presence of oxygen production in complete darkness, without any algae or plants, reinforcing the scientific curiosity around the phenomenon.

Implications for deep-sea mining

The findings challenge the assumption that oxygen production requires photosynthesis. They also have implications for deep-sea mining, as 46 states support a moratorium on seabed exploitation, highlighting the need for further understanding of the deep seabed before mining operations begin.

International debate and future research

A dedicated expedition funded by the Nippon Foundation aims to resolve the scientific debate. The controversy affects international negotiations, as the 31st session of the International Seabed Authority Assembly in August 2026 did not adopt a mining code, with 46 states, including France, supporting a moratorium.