Dark oxygen at the bottom of the ocean – what does it mean?

The oceans remain one of our planet’s greatest mysteries, with experts estimating that our knowledge of them is limited to just 5 percent. of their resources. Recently, however, scientists from the Scottish Society for Marine Science made a groundbreaking discovery at a depth of 4,000. meters, finding an unusual source of one of the world’s most important gases. The discovered dark oxygen could revolutionize our understanding of biological and chemical processes in the marine environment and contribute to new discoveries in evolutionary theory.

Dark oxygen – a mystery in the ocean depths

In 2013. A team of Scottish scientists led by Andrew K. Sweetman has surveyed the seafloor in the Clarion-Clipperton Zone, an area between Hawaii and Mexico that stretches over an area larger than the territory of India. As part of their routine measurements, they placed cylindrical oxygen meters on the ocean floor, sealed tightly to the substrate. It came as a surprise to the scientists to discover that the oxygen levels in the sealed samples were not falling, as they had predicted, but rising. This was because they had expected underwater organisms to consume it intensively.

The Scottish researchers initially put the surprising results down to measurement errors and ignored them, continuing with other research. It was not until eight years later, in 2021. Sweetman went on another expedition, during which he repeated the research, using different technology, and got the same results. And since scientists like to portray unknown phenomena in black colors, the discovery was called dark oxygen.

Where does the oxygen in the ocean come from?

Under normal conditions, oxygen is produced through photosynthesis by plants, algae and some types of bacteria. Although sunlight penetrates to depths of about 1,000 meters, the amount becomes minimal below 200 meters. The presence of oxygen at greater depths in the oceans is due to the better solubility of gases in cold water, which in addition, being more dense, sinks to the bottom. Thanks to this phenomenon, oxygenated water is transported along the ocean floor, which is a key element of the global meridional ocean circulation. This circulation is crucial to the Earth’s climate and weather.

Sweetman’s discovery, however, proves that there must still be some additional source of oxygen at the bottom of the oceans. He was joined in the work to explain this phenomenon by Prof. Franz Geiger of the American Northweestern University in Ilinois. He suggested that salt water in the presence of rusting metals could generate small amounts of electric current. Thus, a simple form of electrolysis could take place at the bottom, leading to the production of dark oxygen.

Indeed, the Clarion-Clipperton field is known worldwide for its abundance of so-called “polymetallic concretions. polymetallic concretions that lie on the ocean floor. These metal nuggets contain, among other things, manganese, nickel, copper and cobalt – elements crucial to the development of modern technology. The extraction of these raw materials is leading to controversy over deep-sea mining.

Dark oxygen under a magnifying glass

To further describe their discovery, the scientists decided to reproduce the hypothetical phenomenon under controlled laboratory conditions. To ensure that no organisms capable of photosynthesis would affect the results, they sterilized the seawater. Sealed samples retested showed a threefold increase in oxygen content. After a few days, oxygen levels stabilized and stopped rising, suggesting that chemical equilibrium had been reached.

Upon closer analysis, it turned out that the polymetallic concretions, popularly known as potatoes because of their characteristic shape, generate a current of 0.95 volts on their surface. This is theoretically not enough to carry out the electrolysis process. However, the presence of dark oxygen is a fact. So what could be the explanation for this phenomenon?

Published in the July 24 issue of Nature Geoscience, the study suggests that the dark oxygen may have been partially formed by an electrolysis process for which polymetallic concretions provided the energy. These are supposed to act like batteries due to potential differences between the ions of individual metals, especially the porous layers of nickel and copper.

But why does an ancient geo-battery, which has existed for millions of years, suddenly start working and then discharge? The study’s authors speculate that dropping the probes on the seafloor and transporting the polymetallic concretions to the laboratory may have caused sediment to fall from their surface, which in turn triggered the process of hydrolysis. The extinction of this phenomenon is most likely related to the exhaustion of potential differences. There is no doubt that this phenomenon will require further in-depth research to better understand the dark oxygen riddle and unveil the full potential inherent in the oceans.

Photo. main: NOAA Ocean Exploration, 2021 North Atlantic Stepping Stones: New England and Corner Rise Seamounts