Sophia Kim '26
Edited by Sophia Gong '26
Light isn’t found 13,000 feet (or 4 kilometers) below sea level; oxygen is consumed there by organisms but definitely not produced. Andrew Sweetman, however, when sampling the ocean depths of the Pacific Ocean, more specifically an area known as the Clarion-Clipperton Zone, found molecular oxygen7. But how could O2 be produced? Surely not by microbes?
From previous scientific data, the expectation was that as depth increases, the amount of dissolved oxygen in the water would decrease until it reaches the oxygen minimum zone (OMZ), found at the bottom of the water column for every ocean, occurring between 100 and 1000 meters below sea level6. And when oxygen reaches 0, it's renamed as the oxygen-deficient zone (ODZ)8. Due to the OMZ’s anoxic (oxygen deficient) nature, some animals like the vampire squid have adapted to slow their metabolism while other oxygen-breathing animals, such as the sperm whales have developed attained migratory patterns between the deeper and shallower zones to adapt to these hypoxic conditions6. Though, in general, most larger animals aren’t able to survive in this zone, despite this many microbes can thrive. It should also be noted that organisms at this level only absorb and don’t contribute to the oxygen content, as there’s no light7.
However, earlier this year, samples from deep oceans have found a higher oxygen concentration than that possible absorbed by water from O2 produced with photosynthesis and dissolved oxygen (DO) directly entering from the atmosphere4,5. An explanation for all this? Seawater electrolysis. Through this, electric currents are able to split water into its respective components of hydrogen and “dark” oxygen7 . More specifically, this is done by polymetallic nodules (made of cobalt, copper, nickel, manganese, etc.), 2.5 km below the Pacific Ocean. Described as “batteries in a rock”, these dark oxygen “factories” have voltages similar to those of “an AA battery” (up to 0.95 V)2,3. This brings into question the extensiveness and diversity of other unknown organisms, enabled to survive with increased oxygen concentrations under the sea, expanding our knowledge with the abyssal ocean ecosystem as well as the origins of life itself with a new oxygen source for planet Earth2.
Yet, as exciting as this sounds, this dark oxygen production (DOP) has been called into question by several individuals and companies (including the Metals Company, the sponsor of this experiment), for they believe the oxygen content may be a result of equipment failure (as this has been an occurrence in the past with Niskin bottles, leading to technological developments from the Pump Profiling System to the Submersible Incubation Devices) from the experiment’s apparatus leaking oxygen or the sample containers accidentally trapping air bubbles1,6. Paired with an unreported control (as it didn’t support Sweetman’s thesis, claimed some) with lower but similar oxygen level patterns as the samples bring about significant scrutiny to the credibility and methodology of this experiment, with testing done by other organizations like the Mining-Impact 2 project and the U.S. Geological Survey’s Global Marine Minerals project1 .Hopefully, more future research will provide a clearer view into the actualities of this matter and, if it were to be true, all the possibilities and tangible applications of this resource.
1. Claim of “dark oxygen” on sea floor faces doubts. Accessed October 19, 2024. https://www.science.org/content/article/claim-seafloor-dark-oxygen-faces-doubts.
2. Sweetman AK, Smith AJ, de Jonge DSW, et al. Evidence of dark oxygen production at the abyssal seafloor. Nature News. July 22, 2024. Accessed October 19, 2024. https://www.nature.com/articles/s41561-024-01480-8#Sec2.
3. “dark oxygen” in depths of Pacific Ocean could force rethink about origins of life. The Guardian. July 22, 2024. Accessed October 19, 2024. https://www.theguardian.com/environment/article/2024/jul/22/dark-oxygen-in-depths-of-pacific-ocean-could-force-rethink-about-origins-of-life.
4. Blog TP arXiv. Dark oxygen is changing the calculus of Extraterrestrial Life. Discover Magazine. August 22, 2024. Accessed October 19, 2024. https://www.discovermagazine.com/the-sciences/dark-oxygen-is-changing-the-calculus-of-extraterrestrial-life.
5. EPA. Accessed October 19, 2024. https://www.epa.gov/caddis/dissolved-oxygen.
6. Microbes in oxygen minimum zones. Schmidt Ocean Institute. July 22, 2024. Accessed October 19, 2024. https://schmidtocean.org/cruise/microbes-in-oxygen-minimum-zones/.
7. Hunt K. Scientists discover “dark” oxygen being produced more than 13,000 feet below the ocean surface. CNN. July 23, 2024. Accessed October 19, 2024. https://edition.cnn.com/2024/07/22/science/dark-oxygen-discovery-deep-sea-mining/index.html.
8. Oxygen minimum zones. Keil Lab Aquatic Organic Geochemistry UW Oceanography. Accessed October 19, 2024. https://depts.washington.edu/aog/oxygen-minimum-zones/.
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