The deep sea is home to “dark oxygen”

THE VAST majority of Earth’s oxygen is made as a by-product of photosynthesis, the use of light to convert water and carbon dioxide into sugars. Any oxygen found in regions where photosynthesis is impossible—such as the abyssal seafloor, a pitch-black realm up to 6,000 metres deep—was thought to be surface gas on the move.In a paper published in , however, Andrew Sweetman at the Scottish Association for Marine Science and his colleagues reveal that some is, in fact, “dark oxygen” created without sunlight.