“Dark oxygen” from deep-sea metal nodules could mean reassessing the origin of life

Potato-sized metallic nodules scattered across some deep-sea regions appear to be producing oxygen.

About half of the oxygen we breathe comes from the ocean, and conventional wisdom has it that this oxygen is the result of photosynthesis by marine plants. But now scientists have discovered that oxygen is also produced by potato-sized metal lumps on the ocean’s abyssal plains—flat regions of the seafloor at depths of 10,000 to 20,000 feet (3,000 to 6,000 meters) where sunlight doesn’t reach. These versatile metal lumps produce this oxygen—called “dark oxygen”—through a process of electrolysis, where seawater (H₂O) is split into oxygen and hydrogen when charged. According to research, only published in the journal Natural Earth ScienceThis charge may arise from the difference in electrical potential that exists between the metal ions within the nodes.

The team behind the study, led by Professor Andrew Sweetman, head of the seabed ecology and biogeochemistry research group at the Scottish Association for Marine Science (SAMS), initially set out to study the impact of polymetallic nodule mining on the seabed ecosystem in the Clarion-Clipperton Zone (CCZ), an abyssal plain that stretches 1.7 million square miles (4.5 million square kilometers) between Hawaii and Mexico. Measuring changes in oxygen levels at various locations, the team expected oxygen levels to decline as they went deeper, but their data showed significant emissions from the seabed.

“When we first got this data [in 2013]We thought the sensors were faulty, because every study ever done in the deep sea had only found oxygen being consumed, not produced. We would go home and recalibrate the sensors, but for 10 years these strange oxygen readings kept coming up,” Professor Sweetman said in a declare. Subsequent measurements using other methods confirmed the results, and Professor Sweetman finally realized that for many years he had overlooked a potentially huge discovery. “For aerobic life to start on this planet, there has to be oxygen, and we understand that Earth’s oxygen supply started with photosynthetic organisms,” he said. “But now we know that there is oxygen being produced in the deep sea, where there is no light. So I think we need to revisit questions like: Where could aerobic life have started?”

The nodules form over millions of years as shell fragments or other debris collect metals dissolved in seawater. Iron oxides and manganese make up most of these metals, but the nodules also contain cobalt, nickel, and lithium, as well as rare earth elements like cerium—essential components of batteries and electronics. These valuable minerals are why many mining companies are turning to the deep sea, and why environmental organizations and agencies like the National Oceanographic and Atmospheric Administration (NOAA) are sounding the alarm about the devastating impact deep-sea mining is having on seafloor ecosystems. petition highlights environmental risks and a call for a moratorium on mining has been signed by more than 800 marine scientists from 44 countries.

One of the scientists who signed the petition, Professor Murray Roberts, a marine biologist from the University of Edinburgh, said BBC News: “There is clear evidence that open-pit mining of deep-sea mineral deposits will destroy ecosystems we barely understand. Because these deposits cover such vast areas of our planet, it is madness to continue deep-sea mining when we know that they could be a significant source of oxygen production.”