A mining test vehicle was dropped by cable into the Pacific Ocean in 1979 and drove across an abyssal plain that was unknown to the majority of people alive at the time. The biological communities that inhabit the Clarion-Clipperton Zone, which is located between Hawaii and Mexico at a depth of around 4,500 meters, function on timelines that don’t correspond to anything in the typical human experience since the water there is so dark and frigid. The test vehicle made tracks in the mud as it went across the seafloor, agitating the material and crushing nodules and the organisms that were connected to them. Then it was raised once more. The experiment was deemed successful. Decades later, researchers went back to the location in the hopes of discovering recovery. They discovered that the traces were still there, bare, and sharp-edged. Nothing had grown back.
The most tangible evidence for comprehending the implications of commercial-scale deep-sea mining for abyssal ecosystems is that discovery, which has been verified by numerous later expeditions. Not a role model. Not a forecast. An actual location that was disrupted once and observed for forty years did not exhibit any discernible biological recovery. The organisms that formerly existed are still extinct. The overturned sediment layers continue to be disturbed. The microbial communities that support the deep seafloor’s complete food chain have not reorganized themselves in a way that is detectable by monitoring tools.
The biology of the deep abyssal plain operates at a speed that is unmatched on the surface. The water is somewhat warmer than freezing. From far above, food comes in the form of a sluggish trickle of marine snow. Because their metabolisms are calibrated for high efficiency over extreme timespans, organisms in this environment have adapted to near-stillness. It takes one to two centimeters per million years for the polymetallic nodules that are the focus of mining activities to form.
In the sense that the word typically suggests, they are not a resource. The animals that live on them, such as xenophyophores, uncommon sponges, polychaete worms, and tiny crustaceans, are specially adapted to that substrate since they are a geological artifact. On the nearby silt plain, they have no access to any other hard surface. The only basis that communities may rely on is eliminated when the nodules are removed. There’s nowhere else for them to go.
The damage is extended beyond the machine’s direct path by the silt plume issue. In addition to crushing the material beneath it, a heavy crawler moving across the seafloor at depth also churns the surrounding silt into suspension, producing a cloud that can travel great distances before resettling. When it settles, it covers organisms, obstructs feeding systems, and disturbs chemical gradients and microbial mats that control nutrient cycling at depth. When plume dispersal is taken into account, the 37% decrease in macrofauna found inside direct disturbance routes underestimates the overall impact of a mining operation.
A variety of national and commercial operators have been granted exploration licenses by the International Seabed Authority over sizable portions of the Clarion-Clipperton Zone; commercial extraction permits are currently undergoing regulatory development. The mineral composition of the nodules—cobalt, nickel, manganese, and copper—that the battery and electronics industries require in significant numbers and that land-based mining provides at its own environmental cost is the main justification for moving further. There is a genuine and honest trade-off. A thorough comparison of the effects of deep-sea mining with those of comparable land-based mining may complicate the story in both directions.
The idea that the damage is transient is something that the 1979 test site does not permit and that no honest accounting of deep-sea mining can discount. There are still the tracks. There is no doubt about the science behind this. It’s simply inconvenient.
