Dark Oxygen: A Deep-Ocean Discovery That Could Change How We See Life on Earth

 

Dark Oxygen: A Deep-Ocean Discovery That Could Change How We See Life on Earth

When we think of oxygen, we picture green forests or vast ocean surfaces shimmering under the sun — places where plants and algae use photosynthesis to turn sunlight into the air we breathe. But now, scientists have uncovered something extraordinary: oxygen being produced in total darkness, 5 kilometers beneath the ocean’s surface.

The phenomenon, dubbed “dark oxygen”, is happening deep in the Pacific Ocean, where no sunlight can reach. Here, on the seabed between Hawaii and Mexico, lie potato-sized lumps of metal called polymetallic nodules. Researchers have found that these nodules can split seawater (H₂O) into hydrogen and oxygen — without any help from plants or photosynthesis.

The Spark Beneath the Waves

The discovery was made by Prof. Andrew Sweetman of the Scottish Association for Marine Science. While studying the deep seafloor back in 2013, Sweetman measured unexpectedly high oxygen levels. At first, he dismissed it — after all, oxygen production without light didn’t fit into established science. But years later, the data kept pointing to the same conclusion: the metallic nodules were acting like natural batteries, producing oxygen in complete darkness.

These nodules form over millions of years as dissolved metals like cobalt, copper, and lithium slowly coat fragments of shell or rock. When clustered together, they can create enough voltage — similar to an AA battery — to electrolyze seawater, releasing tiny bubbles of oxygen and hydrogen.

Life Support in the Deep

Half of Earth’s oxygen comes from the ocean, but before this discovery, scientists believed all of it came from sunlight-driven processes. The idea that the seafloor itself might generate oxygen changes our understanding of deep-sea ecosystems — and possibly, life beyond Earth. If such battery-like reactions can happen on Earth, they could also occur on icy moons or distant planets, creating oxygen-rich environments where life could exist without sunlight.

A Collision Course with Mining Plans

Unfortunately, the same nodules producing “dark oxygen” are also rich in metals critical for modern technology, especially batteries for electric vehicles. This has put them in the crosshairs of deep-sea mining companies.

The Clarion-Clipperton Zone, where this discovery was made, is already being surveyed for large-scale mining operations. But environmental groups and over 800 marine scientists are urging caution. Mining could destroy these fragile ecosystems before we even understand them — potentially wiping out species we haven’t discovered yet and disrupting oxygen production that may sustain life in the deep.

The US National Oceanic and Atmospheric Administration warns that seabed mining could “result in the destruction of life and habitat in the mined areas.” Prof. Murray Roberts of the University of Edinburgh, who signed a petition against deep-sea mining, put it bluntly:

“It would be crazy to press ahead knowing these areas may be a significant source of oxygen production.”

The Next Step

Prof. Sweetman isn’t calling for a complete halt to mining — but he insists that more research is urgently needed. “If we are going to mine the deep ocean, we must do it in the most environmentally friendly way possible,” he says.

The discovery of “dark oxygen” is a reminder that the deep ocean still holds secrets that could reshape our understanding of Earth and life itself. Before we strip it bare for minerals, we may want to pause — and listen to what the seafloor is trying to tell us.