Dark Oxygen

02/09/2024

Scientists have recently discovered "dark oxygen" being generated in the deep ocean by metal-rich lumps on the seafloor. It was previously believed that around half of the oxygen we breathe comes from the ocean, primarily produced by marine plants through photosynthesis, a process that requires sunlight. However, at depths of 5 kilometers, where sunlight doesn't reach, oxygen appears to be produced by naturally occurring metallic nodules, which split seawater (H2O) into hydrogen and oxygen.

A Surprising Deep-Sea Discovery

Several mining companies are planning to harvest these nodules, a move that concerns marine scientists who fear it could disrupt this newly discovered oxygen production process, potentially harming marine life that relies on this oxygen. Lead researcher Prof. Andrew Sweetman from the Scottish Association for Marine Science recalls first observing the phenomenon in 2013: "I saw a significant amount of oxygen being produced in complete darkness on the seafloor. Initially, I ignored it because I was taught oxygen only comes from photosynthesis." Over time, he realized he had overlooked a major discovery.

Prof. Sweetman and his colleagues conducted their research in the deep-sea region between Hawaii and Mexico, an area densely covered with these metal nodules. These nodules, which form over millions of years as dissolved metals in seawater accumulate on shell fragments and other debris, contain valuable metals like lithium, cobalt, and copper, all essential for battery production. This has attracted the interest of many mining companies developing technology to extract them.

However, the "dark oxygen" these nodules produce could be vital for sustaining life on the seafloor. Prof. Sweetman's findings, published in Nature Geoscience, raise significant concerns about the environmental risks associated with proposed deep-sea mining operations. The researchers discovered that the metal nodules generate oxygen by acting like batteries. "When you put a battery in seawater, it starts fizzing," Prof. Sweetman explains, referring to the electric current that splits seawater into oxygen and hydrogen bubbles. He likened the process to a torch requiring multiple batteries to function—the nodules generate enough voltage to split water when they are in contact with each other on the seafloor.

The research team tested this theory in the lab, analyzing the potato-sized nodules and measuring the electric current on their surface. They found that the voltage was nearly equivalent to that of a typical AA battery. This suggests that the nodules on the seabed could generate electric currents strong enough to electrolyze seawater.

This discovery has broader implications, as the researchers speculate that similar battery-powered oxygen production might occur on other moons and planets, potentially creating oxygen-rich environments where life could exist. The Clarion-Clipperton Zone, where this discovery was made, is already a focus for seabed mining companies developing technologies to collect the nodules and bring them to the surface.

Environmental Risks and Future Exploration

However, the US National Oceanic and Atmospheric Administration (NOAA) has warned that seabed mining could lead to the destruction of marine life and habitats in these areas. More than 800 marine scientists from 44 countries have signed a petition urging a pause on mining activities due to the environmental risks involved.

New species are constantly being discovered in the deep ocean, often leading to the observation that we know more about the surface of the Moon than the deep sea. This discovery suggests that the nodules themselves may be a key source of oxygen supporting life in these depths. Prof. Murray Roberts, a marine biologist from the University of Edinburgh, who signed the seabed mining petition, stated, "There’s overwhelming evidence that strip mining deep-sea nodule fields will destroy ecosystems we barely understand. Given the vast areas these fields cover, it would be reckless to proceed with deep-sea mining knowing they could be a significant source of oxygen production."

Prof. Sweetman concluded, "I don't believe this study will stop mining, but it highlights the need for more detailed exploration. We must use the information and data we gather to ensure any future deep-sea mining is conducted in the most environmentally responsible way possible."