“Dark Oxygen” in Deep Ocean

The long-standing belief is that oxygen production relies solely on photosynthesis, which is dependent on sunlight. However, scientists have discovered that oxygen is produced in complete darkness nearly 4,000 meters below the ocean surface. This “dark oxygen” has surprised everyone.

The Clarion-Clipperton Zone (CCZ), a 4.5 million square kilometre area in the Pacific Ocean west of the Americas, is known for its unique geomorphology and potato-shaped nodules. Rich in valuable metals such as nickel, manganese, copper, and cobalt, these polymetallic lumps have attracted mining companies for some time due to their importance for green energy technologies. However, a new study published in Nature Geoscience has revealed that these nodules can also produce oxygen.

Researchers found that these metallic nodules can split water molecules into hydrogen and oxygen, producing oxygen in the pitch-dark environment of the ocean depths. “For aerobic life to begin on the planet, there had to be oxygen and our understanding has been that Earth’s oxygen supply began with photosynthetic organisms,” says Andrew Sweetman, lead author of the study, “But we now know that there is oxygen produced in the deep sea, where there is no light. I think we therefore need to revisit questions like: Where could aerobic life have begun?”

This discovery could significantly alter our understanding of how life began on Earth. Traditionally, it was believed that aerobic (oxygen-dependent) life developed after the emergence of photosynthetic organisms. The fact that oxygen can be produced in the dark depths of the oceans suggests that aerobic life could have originated under different conditions.

The findings will likely have profound implications not only for our understanding of Earth’s early life forms but also for the ongoing debates about deep-sea mining. As scientists continue to explore these metal-rich nodules, often referred to as “batteries in a rock,” the complexity of ocean ecosystems becomes increasingly apparent.

Deep-sea floor organisms naturally consume oxygen, too. However, researchers observed an increase in oxygen levels in these layers, prompting them to investigate the cause. They even eliminated certain microorganisms that were identified to produce dark oxygen in a 2023 study. However, oxygen levels still kept increasing, leading them to focus on the nodules. They found that the high voltage potentials on the nodule surfaces might create an electrolysis effect in seawater, resulting in the production of dark oxygen. The exact mechanism and energy source for this process, on the other hand, are not yet clearly understood.

The impact of this discovery extends beyond our planet. Researchers believe that similar processes could occur on other celestial bodies, such as Jupiter’s moon Europa or Saturn’s moon Enceladus. This suggests that such a process could potentially support life in environments previously considered inhospitable.

As the scientific community processes this groundbreaking discovery, new avenues for research are opening up. And almost definitely, the findings prompt us to reconsider how we interact with and exploit the deep ocean’s resources.