Rare metallic elements found in clumps on the deep-ocean floor mysteriously remain uncovered despite the shifting sands and sediment many leagues under the sea. Scientists now think they know why, and it could have important implications for mining these metals while preserving the strange fauna at the bottom of the ocean.

The growth of these deep-sea nodules — metallic lumps of manganese, iron, and other metals found in all the major ocean basins — is one of the slowest known geological processes. These ringed concretions, which are potential sources of rare-earth and other critical elements, grow on average just 10 to 20 millimeters every million years. Yet in one of earth science’s most enduring mysteries, they somehow manage to avoid being buried by sediment despite their locations in areas where clay accumulates at least 100 times faster than the nodules grow.

Understanding how these agglomerations of metals remain on the open sea floor could help geoscientists provide advice on accessing them for industrial use. A new study published this month in Geology will help scientists understand this process better.

«It is important that any mining of these resources is done in a way that preserves the fragile deep-sea environments in which they are found,» said lead author Adriana Dutkiewicz, an ARC Future Fellow in the School of Geosciences at The University of Sydney.

Rare-earth and other critical elements are essential for the development of technologies needed for low-carbon economies. They will play an increasingly important role for next-generation solar cells, efficient wind turbines, and rechargeable batteries that will power the renewables revolution.

Solving the Enigma

From scouring bottom currents to burrowing animals, researchers have proposed a number of mechanisms to account for this enigma. But solving it depends on a better understanding of where the nodules are situated and the environmental conditions that prevail there. Now a global study published in Geology uses predictive machine learning to investigate which factors control the location of polymetallic nodules. The results offer new insights to inform deep-sea mineral exploration as well as its regulation.

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Materials provided by Geological Society of America. Note: Content may be edited for style and length.