Sweetman, Andrew K., et al. “Evidence of dark oxygen production at the abyssal seafloor.” Nature Geoscience(2024): 1-3.
About half of the oxygen we breath on Earth comes from the ocean – from the photosynthesizing phytoplankton living at the ocean’s surface; and for the longest time, scientists believed that this oxygen from the surface ocean sinks to the bottom to provide an oxygenated habitat for deep sea creatures. However, a set of scientists have now found that the deep ocean is in fact capable of producing its own oxygen – now termed ‘dark oxygen’!
The Bottom of the Pacific
These scientists were studying oxygen levels in the Clarion-Clipperton Zone (CCZ), an area of the Pacific Ocean located between Hawaii and Mexico. They sent an instrument all the way down to the sea bed (over 4000 meters or 13,000 feet!) which consists of a cylindrical chamber that encloses a part of the seabed so that no oxygen and get in and out of the chamber. In most parts of the ocean, such an instrument shows that the oxygen level decreases in the chamber over time because the oxygen is being used up by breathing organisms trapped inside the chamber.
But to the scientists surprise, the chambers at the bottom of the CCZ showed an increase in oxygen levels instead of the expected decrease! Something was creating oxygen at the same time the oxygen was being used up by the trapped organisms.
Potato Battery – but ocean style
The CCZ is known to be home to polymetallic nodules – large rock-like deposits on the sea floor which contain many valuable metals that are mined by humans to make batteries and various electronic components for our phones and computers.
These nodules were found to be the source of the extra oxygen the scientists had observed in their data. The metal in the nodules is able to react with the salty sea water via a process known as electrolysis– breaking the water molecules to create oxygen and release it in the deep sea.
To prove this hypothesis, the scientists brought some nodules to the lab, put them in salt water, and probed them with electrodes – much like sticking electrodes in a potato to make a battery! They saw that the nodules were able to produce voltages of about 1 volt – which is similar to a AA battery – making the water bubble – indicating the splitting of water molecules and the release of oxygen.
What’s Next?
We now know that mining the polymetallic nodules may lead to the loss of an important source of oxygen for the organisms to breathe in the deep ocean – and could negatively impact the deep ocean ecosystem. Which is why this research is extremely relevant – as it will inform the International Seabed Authority of the risks of deep-sea mining.
This research also shows that oxygen can be produced even without photosynthesis – which means that life on our planet could have begun before the rise of photosynthesis about 3 billion years ago in the deep, dark ocean!
I am a PhD student at the University of Chicago and the Marine Biological Lab, currently studying germline development and regeneration in the amphipod crustacean, Parhyale hawaiensis. I did my undergraduate degree in India and did my Masters in Oceanography at the University of Massachusetts (during which I participated in multiple month-long research cruises out in the Pacific and Atlantic Ocean!). I am broadly interested in integrating ecology with developmental biology in marine organisms and I hope to comprehend the fundamental interconnectedness of the mysteries that swim in the Earth’s oceans. I am also an illustrator and a PADI certified diver.
