Dark oxygen produced by deep sea ‘batteries’

Scientists have discovered “dark oxygen” being produced deep in the ocean, apparently by mineral deposits on the sea floor.

About half of the oxygen we breathe comes from the ocean. But before this discovery, it was understood that this oxygen was produced through photosynthesis by marine plants, which requires sunlight.

Here, at a depth of 5 kilometers, where sunlight cannot penetrate, oxygen appears to be produced by natural mineral “nodules” that split seawater – H2O – into hydrogen and oxygen.

Several mining companies plan to collect these nodules, which marine scientists fear could disrupt the newly discovered process — and harm any marine life that depends on the oxygen they produce.

“I first saw this in 2013 – a huge amount of oxygen being produced on the seafloor in complete darkness,” says lead researcher Professor Andrew Sweatman from the Scottish Society for Marine Science. “I ignored it, because I had been taught – you only get oxygen through photosynthesis.

“In the end, I realised that I had been ignoring this potentially huge discovery for many years,” he told BBC News.

He and his colleagues conducted their research in a deep-sea area between Hawaii and Mexico—part of a vast expanse of seafloor covered in these mineral nodules. The nodules form when minerals dissolved in seawater accumulate on fragments of shells—or other debris. It’s a process that takes millions of years.

Since these nodules contain minerals such as lithium, cobalt and copper — all of which are essential for making batteries — many mining companies are developing technology to collect them and bring them to the surface.

But Professor Sweatman says the dark oxygen produced by these organisms could also support life on the sea floor. His discovery, published in the journal Nature Geoscience, raises fresh concerns about the risks of proposed deep-sea mining projects.

Scientists have discovered that mineral nodules are able to produce oxygen precisely because they act like batteries.

“If you put a battery in seawater, it starts to fizz,” explained Professor Sweetman. “This is because the electric current splits the seawater into oxygen and hydrogen.” [which are the bubbles]“We believe this is what happens with these nodules in their natural state.”

“It’s like a battery in a torch,” he added. “If you put one battery in, it won’t light up. If you put two batteries in, you’ll get enough voltage to light the torch. So when the nodes sit on the seafloor in contact with each other, they work in unison – like multiple batteries.”

The researchers tested this theory in the lab, collecting and studying potato-sized blocks of metal. They measured the voltage across the surface of each block of metal—basically, the strength of the electric current. They found that the voltage was roughly the same as the voltage in a typical AA battery.

This means, they say, that nodules on the seafloor could generate electric currents large enough to split or electrolyze seawater molecules.

Researchers believe the same process — producing oxygen using a battery that doesn’t require any light or biological processes — could happen on other moons and planets, creating oxygen-rich environments where life could thrive.

The Clarion-Clipperton Zone, where the discovery was made, is already being explored by a number of seabed mining companies, which are developing technology to collect the nodules and transport them to a surface vessel.

The US National Oceanic and Atmospheric Administration has warned that seabed mining operations could “destroy life and seabed habitats in mined areas.”

More than 800 marine scientists from 44 countries participated in the event. I signed a petition Highlighting environmental risks and calling for a moratorium on mining activity.

New species of life are being discovered in the deep ocean all the time – it’s often said that we know more about the surface of the moon than we do about the deep sea. This discovery suggests that the nodules themselves may provide the oxygen needed to support life there.

Professor Murray Roberts, a marine biologist from the University of Edinburgh, is one of the scientists who signed the seabed mining petition. He told BBC News: “There is already overwhelming evidence that surface mining of deep-sea nodule fields would destroy ecosystems that we barely understand.”

“Since these fields cover huge areas of our planet, it would be crazy to proceed with deep-sea mining knowing that they could be an important source of oxygen production.”

“I don’t see this study as putting an end to mining,” Professor Sweetman added.

“[But] “We need to explore it in more detail, and we need to use this information and the data we collect in the future if we are going to go into the deep ocean and extract it in the most environmentally friendly way.”