The Discovery of Dark Oxygen: A Hidden Source of Life in the Depths

In the deep, lightless realms of the Pacific Ocean—where pressure crushes and sunlight never penetrates—scientists have made a groundbreaking discovery: dark oxygen. Unlike the oxygen we are familiar with, produced by plants and photosynthesis, dark oxygen forms without light, deep in the sediments of the ocean floor.

By Eric Herman

For generations, scientists believed that oxygen production was the solely domain of photosynthetic organisms—plants, algae, and cyanobacteria that contain chlorophyl and rely on sunlight. That was until recently as a set of groundbreaking deepwater discoveries has changed our understanding of how oxygen can be generated, even in the darkest corners of the ocean.

This newly recognized phenomenon has been heralded as big news by scientists and researchers the world over. Many believe it has the potential to reshape how we view underwater ecosystems and the resilience of life in extreme environments, as well as reshaping our understanding biogeochemistry, and even the origins of life itself.

In oxygen-deprived areas of the ocean, scientists previously assumed that only anaerobic (non-oxygen-using) organisms could survive. However, recent studies revealed the presence of small but measurable amounts of molecular oxygen in these “anoxic” zones—without any sunlight to drive photosynthesis. How was this possible?

Researchers have traced this oxygen to a previously underestimated chemical pathway: the microbial breakdown of nitrite into nitrogen and oxygen. This process, called dismutation, allows certain bacteria to “split” nitrite, producing free oxygen molecules in the absence of light. These microbes belong to a group known as nitrite-oxidizing bacteria, and their existence in anoxic marine zones implies a previously hidden web of oxygen-based life quietly thriving in the deep.

There are other theories, listed below, but there is little doubt the implications of this discovery are profound. It helps explain how fish and other aerobic organisms survive in low-oxygen environments and offers a new window into the biogeochemical cycles of the Earth. Dark oxygen production could also have played a role in the early development of life on Earth and may influence the search for life on other planets.

SEARCHING IN THE DARK

The process of discovering dark oxygen began in 2021. Scientists working off the coast of Peru and in the eastern tropical North Pacific found that certain microbes within deep-sea sediments were producing oxygen in total darkness.

To date Dark oxygen has been discovered in groundwater aquifers and deep subsurface environments, such as deep groundwater in parts of Canada, particularly in Alberta, isolated aquifers around the world, including South Africa and Finland, and in scattered sediments and subsurface ecosystems far from any light source.

These environments are typically anoxic (lacking oxygen), yet scientists measured trace amounts of dissolved oxygen, which couldn’t be explained by contamination or atmospheric mixing.

Most recently potentially massive stores of dark oxygen were found nestled between Hawaii and the western coast of Mexico in the Pacific Ocean’s Clarion-Clipperton Zone (CCZ), a 4.5 million-kilometer-square area of abyssal plain bordered by the Clarion and Clipperton Fracture Zones. Although this stretch of sea is a vibrant ecosystem filled with marine life, the CCZ is known best for its immense collection of potato-sized rocks known as polymetallic nodules.

Estimated to potentially number in the trillions, are filled with rich deposits of nickel, manganese, copper, zinc, cobalt. Those particular metals are vital for the batteries needed to power a green energy future, leading some mining companies to refer to nodules as a “battery in a rock.”

However, a study reports that these nodules might be much more than simply a collection of valuable materials for electric cars—they also produce oxygen 4,000 meters below the surface where there is only darkness.

The rocks could also rewrite the script on not only how life began on this planet, but also its potential to take hold on other worlds within our Solar System, such as Enceladus or Europa. 

HOW IT’S MADE

Researchers propose several non-photosynthetic pathways for this “dark” oxygen production:

• Microbial dismutation of nitric oxide (NO): Certain microbes can convert NO into N₂ and O₂ without sunlight.
• Water radiolysis: Natural radioactive decay in rocks splits water (H₂O) into hydrogen and oxygen.
• Perchlorate or chlorate respiration: Some bacteria can use these compounds and release O₂ as a byproduct.

On a biological level, the discovery suggests that oxygen—and therefore complex life—could have originated and evolved in lightless, extreme environments.

This opens a new window into early Earth’s history. For billions of years, Earth’s atmosphere lacked free oxygen, a period known as the Archean Eon. Scientists previously thought life during this time was exclusively anaerobic. But the presence of dark oxygen-producing bacteria suggests that oxygenic niches might have existed long before the planet’s atmosphere became oxygen-rich during the “Great Oxidation Event” about 2.4 billion years ago.

It also extends the possibility of life on other celestial bodies. Europa, Enceladus, and even Mars, which have underground water reservoirs or frozen oceans, may host microbial life capable of surviving in the dark—and possibly producing dark oxygen.

POTENTIAL RESOURCE

The discovery of dark oxygen also has potential applications in energy and climate science. Because this process happens without light or high temperatures, it could inspire novel forms of bioengineering that generate oxygen in closed, off-grid, or extraterrestrial environments—ideal for long-term space missions or deep-sea exploration.

Additionally, understanding how these microbes interact with carbon and nitrogen cycles can inform climate models. The ocean floor plays a significant role in storing carbon and moderating global temperatures. If oxygen is being produced and consumed in these sediments, it changes the rates of decomposition, methane release, and nutrient cycling, all of which have implications for greenhouse gas fluxes and climate feedback loops.

To harness or even study dark oxygen further, scientists will need a suite of advanced tools and approaches:

• Ultra-sensitive oxygen sensors capable of detecting micro-variations of O₂ in sediment porewater at nanomolar levels.
• Genomic sequencing technologies to identify and map the DNA of microbes responsible for nitrite dismutation.
• Autonomous underwater vehicles (AUVs) equipped with sediment-sampling drills and real-time geochemical analyzers.
• Laboratory simulation tanks that replicate high-pressure, anoxic environments for controlled experiments on microbial metabolism.
• Synthetic biology platforms that could potentially engineer or replicate dark oxygen-producing microbes for use in closed ecosystems (like Mars habitats or biospheres).

As we explore the ocean floor with ever-increasing precision, we may find that life is not only more adaptable than we imagined, but that its survival strategies hold the keys to humanity’s future on Earth and beyond.

This hidden form of oxygen, born in the shadows of the deep sea, may one day sustain new forms of life in places we never dreamed possible, or even help us cool a warming planet.

Key References

 Evidence of dark oxygen production at the abyssal seafloor. Sweetman, A.K., Smith, A.J., de Jonge, D.S.W. et al.National Geoscience. 17, 737–739 (2024).

4,000 Meters Below Sea Level, Scientists Have Found the Spectacular ‘Dark Oxygen’ Darren Orf, Popular Mechanice, April 6 (2025).

Dark Oxygen Production in the Deep Ocean, Sustainable Ocean Alliance, SOA Team, July 2024.

Opening illustration by Maxim Gaigul | Shutterstock