The lump on this shot looks like a black-brown cauliflower. In fact, there is a potentially important deep-sea metal supplier behind the strange tuber.
They are black-brown and spherical or cauliflower-shaped, grow as if in slow motion and are often only a few centimeters tall: the manganese nodules. They are located in ocean depths of at least 4,000 meters and there cover the sea floor in huge amounts. The largest deposits of manganese nodules lie loosely on the bottom of the Pacific. Tens of thousands of tons of the tubers have already been discovered in one region in the Central Pacific alone.
Although the black lumps look strange, like the specimen populated by a white deep-sea sponge in our photo, they could become significant: Manganese nodules are considered to be promising sources of the eponymous manganese as well as copper, nickel, cobalt, zinc and other metals.
These ore lumps could arise because metals dissolved in seawater have accumulated on micrometer-sized bacteria over the course of millions of years. The microorganisms serve as crystallization nuclei, which promote the adhesion of ever new metal ions to the protein layer on its outer wall. Over time, new metal layers are created.
The valuable metals of the manganese nodule come from the sediment of the sea and also directly from the underground rock. Due to the large-scale ocean circulation, water penetrates the porous rock beneath the sediments, so that heat and chemical constituents are withdrawn from the ocean floor. The metals are leached out and reach the ocean floor, the water close to the ground and the deep-sea nodules on the ocean floor.
As natural metal suppliers, the manganese nodules arouse desires: In regions with high raw material deposits – such as the so-called Clarion-Clipperton fracture zone, which extends from Mexico to Hawaii – Germany, among others, has already secured license areas for deep-sea mining of the ore lumps. But mining in the depths of the oceans is considered to be very costly and environmentally harmful. The harvesting of the manganese nodules with the help of remote-controlled collector machines stirs up sediment, causes noise and turbulence and destroys and changes the sensitive environment of the animals over decades.
German scientists have been researching the possible consequences of deep-sea mining in the Clarion-Clipperton Zone in the Pacific for a long time. As part of the “MiningImpact” project, they have now started an expedition to evaluate the effects of the collector vehicles and to find mining routes that minimize damage to the deep-sea ecosystem.