Nestled between Hawaii and the west coast of Mexico lies the Clarion-Clipperton Zone (CCZ) of the Pacific Ocean, a 4.5 million-square-kilometer abyssal plain. While this expanse of sea is a vibrant ecosystem teeming with marine life, the CCZ is best known for its massive collection of potato-sized rocks called polymetallic nodules. These rocks, of which there are potentially billions, are filled with rich deposits of nickel, manganese, copper, zinc, and cobalt. These metals in particular are essential for the batteries needed to power a green energy future, leading some mining companies to refer to the nodules as a “battery in a rock.” But a new study reveals that these nodules may be more than just a collection of valuable materials for electric cars: They also produce oxygen 4,000 meters below the surface, where sunlight can’t reach. This unexpected source of “dark oxygen,” as it’s called, redefines the role of these nodules in the CZZ. The rocks could also rewrite the script not only for how life emerged on this planet, but also for its potential to take root on other worlds in our solar system, such as Enceladus or Europa. The results of this study were published in the journal
Nature Geoscience .“For aerobic life to begin on the planet,” said Andrew Sweetman, a deep-sea ecologist at the Scottish Association for Marine Science and lead author of the study, “there had to be oxygen, and we thought that photosynthetic organisms were responsible for the Earth’s oxygen supply. But we now know that oxygen is produced in the deep sea, where there is no light. So I think we have to come back to questions like: where could aerobic life begin?
The journey to this discovery began more than a decade ago, when Sweetman began analyzing how oxygen levels decreased as it sank deeper into the ocean. So he was surprised in 2013 when sensors revealed increased oxygen levels in the CCZ. At the time, Sweetman believed the data was due to faulty sensors, but later studies showed that this abyssal plain was somehow producing oxygen. Noting the nodule’s slogan “a battery in a rock,” Mr. Sweetman wondered whether the minerals in these nodules were acting as a kind of “geobattery” by separating hydrogen and oxygen through electrolysis of sea water.
A study in 2023 showed that various bacteria and archaea can create “dark oxygen.” So Sweetman and his team recreated CCZ conditions in the laboratory and eliminated all the microorganisms using mercuric chloride; Surprisingly, oxygen levels continued to rise. According to
ScientificAmerican , Sweetman found a voltage of about 0.95 volts on the surface of these nodules, which are probably charged as they grow with different deposits growing unevenly throughout, and this natural charge is sufficient to divide sea water.Scientists have discovered dark oxygen, produced 4,000 meters deep in the ocean
In response to this finding, Lisa Levin of the Scripps Institution of Oceanography, who was not involved in the study, stressed, in a comment to the Deep Sea Conservation Coalition, the importance of a moratorium for protection of these deep water nodules:
This is a prime example of what it means for the deep ocean to be a frontier, a relatively unexplored part of our planet. There are still new processes to be discovered that challenge what we know about life in our oceans. Oxygen production on the seafloor by polymetallic nodules is a new ecosystem function that needs to be considered when assessing the impact of deep-sea mining. These findings highlight the importance of encouraging independent deep-ocean scientific research worldwide to inform deep-ocean policy.
The ISA continues to negotiate with key stakeholders on the regulation of deep-sea mining and met for two weeks in April to discuss new elements of the negotiation. This council will operate with a “roadmap for future work” until the end of July 2024.
So, as the future of the world’s oceans approaches a critical conservation or exploitation moment, science has once again shown that disrupting these ecosystems could have consequences we cannot even imagine.