Nodules in the deep sea may be a source of ‘dark oxygen’

Strewn across the Pacific Ocean's seafloor, potato-sized rocks called nodules are a treasure in the deep sea. Not only are they rich in critical minerals needed for clean energy technologies, but the rocks also often serve as the only anchoring point for many delicate deep-sea creatures. Now a new study suggests the nodules are able to produce oxygen about 4,000 m below the ocean's surface ( Nat. Geosci. 2024, DOI: 10.1038/s41561-024-01480-8 ). Almost a decade ago, while sampling the seabed in the Clarion-Clipperton Zone—a region in the northeast Pacific Ocean known for its vast manganese nodule beds—Andrew Sweetman, a marine ecologist with the Scottish Association for Marine Science, noted unexpected oxygen readings. With no light at such dark depths, photosynthesis couldn't be an explanation for what seemed like ongoing oxygen production. Assuming faulty equipment, "we would come home and recalibrate the sensors, but, over the course of 10 years, these