The ocean is pumping oxygen from its abyss

How is the deep seabed, containing no photosynthetic organisms, releasing oxygen?

Polymetallic nodules, potato-sized metal-containing solids, found 13,000 feet below the Pacific Ocean. At depths of 13,000 feet, where sunlight cannot penetrate, these nodules are producing oxygen. | Photo Credit: Camille Bridgewater, Northwestern University

Deep beneath the Pacific Ocean’s surface, a curious phenomenon has been discovered. At depths of 13,000 feet, where sunlight cannot penetrate, “polymetallic nodules” are producing—hold your breath—oxygen. These potato-sized, metal-containing solids grow at an incredibly slow rate of 1 millimetre per million years.

The nodules “could play a part in the oxygen production by catalysing the splitting of water molecules”, explains an article in the latest edition of Nature.

The discovery was first made a decade ago, when researchers delved into the sea floor in an area larger than India, between Hawaii and Mexico. The scientists’ aim was to evaluate the potential for mining metal-rich nodules. The researchers used “benthic chamber experiments” that involve sending a very advanced can down to the deepest part of the ocean; the benthic zone (in Greek, benthos means “the depths”) is at around 4 km depth in this case.

Co-author of the study Andrew Sweetman initially believed that the records were due to a “sensor malfunction” as this deep seabed contained no photosynthetic organisms that could release oxygen.

Dark oxygen production

So how copious is the oxygen production? “We don’t know the production [of oxygen] rate yet but it is certainly one aspect of grant proposals that we are now putting together,” co-author of the paper, Franz Geiger, Technological Institute, Northwestern University, Evanston, US, told Frontline.

“It seems likely that other nodule-rich areas, of which there are plenty around the world, will produce oxygen as well but additional research is needed. There are large deposits south in the Indian Ocean,” said Geiger.

“Future studies of DOP [dark oxygen production] in the deep sea may also shed light on broader relationships between metal-oxide deposition, biological evolution and the oxygenation of Earth,” the research paper notes.

Dark oxygen can be produced in Earth’s oceans; it may also be, at least in principle, possible on other ocean-bearing moons and planetary bodies, Geiger explained. “Scientists believe that Saturn’s Encedalus and Jupiter’s Europa are ocean moons with a salty “dark ocean” underneath a thick layer of ice. The elements found in the nodules on earth, such as nickel, cobalt, manganese, and iron, are common in the bodies of the solar system, so they may be present on ocean moons as well. We hypothesised dark oxygen mechanism may then be relevant for the oxygenation of those dark oceans as well, if they indeed contain oxygen.”

A source for early life?

The prevailing mechanism of oxygen production on the earth is rooted in photosynthesis by cyanobacteria (green algae), which started over two billion years ago. “But these organisms need sunlight, so the photosynthesis mechanism won’t operate where the nodules are located. Here is now an additional oxygen formation mechanism that operates in the dark, producing oxygen that may have been a source for early life, and perhaps enabled its formation and evolution, at the bottom of the sea floor,” Geige added.

Sweetman said in a video: “What we are showing now is that the deep sea is able to produce its own oxygen… The other implication of this research is that it potentially sheds light on where life began on the planet. This discovery has shown that well, maybe, there was another source of oxygen a long time ago, and aerobic life, of life that breathes oxygen, could have persisted before the rise of photosynthesis. And if it is happening on our planet, it could be happening on other planets too.”