Scientists discover unexpected 'dark-oxygen' in deep sea

In 2013, ocean scientist Andrew Sweetman noticed a strange phenomenon while studying the Pacific Ocean's seafloor. His equipment showed that oxygen was being produced at a depth of 4,000 meters (about 13,100 feet), where no light can reach. Initially, Sweetman thought his sensors were faulty, but repeated tests confirmed they were working correctly.

Sweetman's research team found oxygen being produced without photosynthesis, which is unexpected as previous studies showed deep-sea organisms only consume oxygen. This discovery challenges existing assumptions about oxygen production in the ocean.

Their study, published in Nature Geoscience, highlights the unknown aspects of ocean depths and the potential impact of deep-sea mining. The team first observed this "dark" oxygen production while studying marine biodiversity in an area rich in polymetallic nodules, which contain valuable metals like cobalt, nickel, copper, lithium, and manganese. These metals are essential for green technology but extracting them could harm underwater ecosystems.

Sweetman used a deep-ocean lander to measure oxygen levels and noticed that oxygen was being produced, not consumed. It took him until 2021 to accept this finding and investigate further. He collaborated with electrochemist Franz Geiger and discovered that the nodules themselves might act like natural batteries, producing oxygen through a process similar to seawater electrolysis.