Researchers have uncovered a puzzling source of oxygen at the bottom of the ocean, where it should not exist. At depths of around 4,000 meters, where sunlight cannot reach and conditions are completely dark, oxygen typically disappears rather than forms. However, repeated measurements have shown that oxygen levels in this area actually increase. Scientists suspect that tiny metallic nodules on the seabed may be responsible for this unusual phenomenon. Andrew Sweetman, a deep-sea ecologist at the Scottish Association for Marine Science (SAMS), has studied the respiration of the seabed, a process he describes as "the heartbeat of the ocean." Since 2021, he has led several expeditions in the Clarion-Clipperton zone, a vast, deep abyssal plain located between Hawaii and Mexico. This region is one of the deepest parts of the world’s oceans and is permanently dark. In 2012, Sweetman discovered that the seabed’s "heartbeat" sometimes behaved irregularly. Using underwater instruments equipped with optical oxygen sensors, he measured oxygen levels at about 4,000 meters in the Intertropical Convergence Zone (ITCZ). The data revealed a surprising result: oxygen levels were higher at that depth than they were in shallower waters, according to Popular Mechanics. At first, Sweetman thought the equipment might be faulty, as he had been taught that oxygen production requires photosynthesis, which needs sunlight. However, repeated measurements confirmed that the data was accurate. The only explanation was the existence of "dark oxygen," produced by an unknown underground mechanism that does not rely on solar light. After conducting similar measurements in other oceanic environments, Sweetman concluded that the ITCZ might be the only region where this phenomenon occurs. Years of research led him to consider the role of manganese nodules—small, metallic structures found on the seabed. Sweetman explains that if a battery is submerged in seawater, it breaks down into oxygen and hydrogen. If millions of such "batteries" existed on manganese oxide particles within the nodules, and electrons flowed through the internal structure of the manganese, this could explain the oxygen production. The key to the mystery, he says, lies in the presence of these manganese nodules, which were first discovered in 1868 in the Kara Sea off the Siberian coast. Manganese nodules, though seemingly insignificant, are actually millions of years old and form through one of the slowest geological processes on Earth. Chemist Franz Geiger, who has collaborated with Sweetman, compares their formation to "a game of Tetris in slow motion," as dissolved ions from the water slowly build structures from the bottom up. Since the oceans contain only trace amounts of metal ions, these nodules grow extremely slowly over vast periods of time, under immense pressure and low temperatures along the abyssal plain. Laboratory tests confirmed that without these nodules, oxygen levels decrease as expected. But when they are present, oxygen levels increase. Now, mining companies are showing interest in exploiting these deep-sea nodules, found in various regions of the world’s oceans, including the Cook Islands and the Baltic Sea. This scientific discovery may soon attract companies eager to harness the potential of these natural, underwater batteries.