This research reveals a surprising discovery about how oxygen behaves in deep-sea areas of the Pacific Ocean, specifically where polymetallic nodules (rock-like structures rich in metals) are found.
Researchers conducted experiments in the Clarion–Clipperton Zone (CCZ), an area known for its abundance of nodules, and observed something unexpected: oxygen levels increased rather than decreased. This phenomenon is called “dark oxygen production” (DOP).
Expected Oxygen Consumption vs. Observed Oxygen Production
In most deep-sea environments, organisms consume oxygen and chemical processes in the sediments deplete it. However, the researchers observed a significant rise in oxygen levels over time in multiple experiments. Oxygen concentrations in the chambers tripled within 48 hours. This unexpected oxygen increase pointed to DOP, a process not previously observed in deep-sea environments.
Experimental Setup and Methodology
To verify their results, the researchers deployed benthic chambers at the seafloor and monitored oxygen concentration changes. They cross-checked their measurements with Winkler titration to ensure accuracy. The team also tested various conditions, such as adding nutrients, dead algae, and other substances. Despite these changes, the oxygen increase remained consistent across all treatments, confirming that DOP was not caused by biological activity.
Ruling Out Alternative Explanations
The researchers carefully eliminated other possible explanations. They ensured that oxygen wasn’t entering the chambers through trapped air bubbles or diffusion from the chamber materials. The steady rise in oxygen over several hours in multiple experiments indicated that the oxygen increase was not due to any experimental errors or external influences.
Role of Polymetallic Nodules in Oxygen Production
The team found that the polymetallic nodules played a crucial role in oxygen production. These nodules, composed of metals like manganese, nickel, and copper, exhibited electrical potentials of up to 0.95 volts on their surfaces. This electrical potential likely triggers electrochemical reactions, particularly electrolysis, which splits water into oxygen and hydrogen. The nodules essentially function as “geo-batteries,” generating oxygen through electrochemical processes.
The researchers observed that larger nodules, with greater surface areas, produced more oxygen, supporting the theory that the nodules act as geo-batteries and release oxygen into the surrounding water.
Implications for Deep-Sea Ecosystems
This discovery challenges previous understanding of oxygen dynamics in deep-sea ecosystems. The oxygen produced by these electrochemical processes could help support organisms living on the seafloor, potentially affecting the oxygen cycle in abyssal ecosystems. However, the researchers caution that DOP is likely not a continuous process and may vary depending on nodule size and type
Concerns About Deep-Sea Mining
The study raises concerns about the potential impact of deep-sea mining on these oxygen production processes. Mining activities that disturb the polymetallic nodules could interfere with the electrochemical reactions responsible for DOP, potentially damaging the ecosystems that rely on it.
Conclusion
In conclusion, the study uncovers a new mechanism of oxygen production in the deep sea, driven by the electrochemical properties of polymetallic nodules. This finding challenges existing knowledge and raises new questions about the role of nodules in marine ecosystems. Further research is necessary to fully understand the implications of these findings, particularly in light of the potential impacts of deep-sea mining on these processes.
Source: Nature Geoscience (Nat. Geosci.)
