“Dark oxygen” created in the ocean without photosynthesis, researchers say

Researchers have discovered bundles of “dark oxygen” being formed on the ocean floor. 

In a new study, over a dozen scientists from across Europe and the United States studied “polymetallic nodules,” or chunks of metal, that cover large swaths of the sea floor. Those nodules and other items found on the ocean floor in the deep sea between Hawaii and Mexico were subjected to a range of experiments, including injection with other chemicals or cold seawater. 

The experiments showed that more oxygen — which is necessary for all life on Earth — was being created by the nodules than was being consumed. Scientists dubbed this output “dark oxygen.” 

About half of the world’s oxygen comes from the ocean, but scientists previously believed it was entirely made by marine plants using sunlight for photosynthesis. Plants on land use the same process, where they absorb carbon dioxide and produce oxygen. But scientists for this study examined nodules about three miles underwater, where no sunlight can reach. 

This isn’t the first time attention has been drawn to the nodules. The chunks of metal are made of minerals like cobalt, nickel, manganese and copper that are necessary to make batteries. Those materials may be what causes the production of dark oxygen. 

“If you put a battery into seawater, it starts fizzing,” lead researcher Andrew Sweetman, a professor from the Scottish Association for Marine Science, told CBS News partner BBC News. “That’s because the electric current is actually splitting seawater into oxygen and hydrogen [which are the bubbles]. We think that’s happening with these nodules in their natural state.”

The metals on the nodules are valued in the trillions of dollars, setting of a race to pull the nodules up from the ocean’s depths in a process known as deep sea or seabed mining. Environmental activists have decried the practice.  

Sweetman and other marine scientists worry that the deep sea mining could disrupt the production of dark oxygen and pose a threat to marine life that may depend on it. 

“I don’t see this study as something that will put an end to mining,” Sweetman told the BBC. “[But] we need to explore it in greater detail and we need to use this information and the data we gather in future if we are going to go into the deep ocean and mine it in the most environmentally friendly way possible.”