Deep-sea mining is the process of retrieving mineral deposits from the ocean floor at depths below 200 m. As terrestrial resources are becoming scarcer and demand for precious metals is rising, especially in countries such as China, Japan, Korea and India, there has been an increasing interest in sourcing minerals from the deep-sea marine environment. Deep-sea deposits are rich in nickel, cobalt, copper and manganese – minerals that are essential in energy storage and electrical systems. As such, many people believe that exploiting these deep-sea resources is the key to securing a greener, low-carbon future for mankind.
The Final Frontier
However, these deep-sea environments consist of 65% of the ocean floor surface area and contain 95% of the volume of the ocean making it the most extensive habitat for life on earth. Commonly, referred to as the final frontier, the deep-sea is one of the most unexplored regions on earth and there is still much that we do not understand about this environment and its inhabitants.
What we do know is that life below 200 m is harsh. With very little to non-existent sunlight, extreme pressures and freezing temperatures, the creatures that live here are unusual and uniquely adapted to their environment. They are generally slow growing but extremely long-lived – with some coral colonies believed to be thousands of years old. Unfortunately, it also makes them unusually sensitive to anthropogenic disturbances and very slow to recover so we should proceed with caution if we are intent on mining these habitats. As with all mining practices, there is potential for environmental degradation and habitat loss which could lead to the collapse of many of the least understood and fragile ecosystems on the planet and without a better understanding of what the impact of this will be we could cause irreversible damage.
The Deep-sea Environment And Potential Sources Of Minerals
There are three main marine environments which provide possible sources of deep seabed metal-bearing minerals: polymetallic nodules on abyssal plains, polymetallic crusts which have formed on the surface of seamounts (an undersea mountain formed by volcanic activity) and the sulfide deposits formed by hydrothermal vents (both active and inactive).
While companies are still exploring the deep-sea mining potential and are in the development phase of extraction, most strategies for deep-sea mining employ machines that travel along the ocean floor and send collected material up a riser and lifting system to a ship waiting on the sea surface. Slurry is then returned to the ocean floor through another pipe.
Unfortunately, these environments are also associated with higher faunal abundance and biodiversity than other regions of the seafloor.
Polymetallic Nodule Fields On The Abyssal Plains
Polymetallic nodule fields, for instance, form some of the only hard surfaces on the soft pelagic red clay ocean floor and are associated with a more abundant and diverse community of macroorganisms than those found in regions with low concentrations of nodules. Some species, such as octopuses, fish, crinoids and corals, have also been observed to inhabit nodule fields even though they are not usually found on the surrounding soft substrate areas.
Despite the apparent low biomass on the soft ocean floor on the abyssal plains, there is also a very high diversity here of bacteria, protozoans and invertebrates such as worms, crustaceans, sponges, mollusks and echinoderms. Vertebrate species found here include pelagic and demersal fish such as viperfish, anglerfish and gulper eels.
Polymetallic Crusts On Seamounts
Seamounts are also associated with largely endemic and highly diverse communities and are considered biodiversity hotspots. Roughly 800 species of fish are found associated specifically with seamounts as well as a variety of reef-forming filter feeders, such as corals and sponges. Reefs enhance local biodiversity by increasing the complexity of the habitat and creating niches for other creatures, and thus attracting other organisms such as mollusks, crustaceans and echinoderms. In addition, seamount habitats are commonly visited by pelagic organisms such as sharks, tuna, cetaceans and sea turtles.
Sulfide Deposits From Hydrothermal Vents
Hydrothermal vents, where sulfide deposits are found, are also home to unique and thriving ecosystems in which the primary producers are chemosynthetic and form organic matter using the energy generated from the oxidation of inorganic compounds, such as hydrogen sulfide, instead of energy from the sun. Despite the intense heat, many organisms, such as worms, shrimps and crabs inhabit these environments.
Potential Impacts Of Deep Sea Mining:
The removal of polymetallic nodules and harvesting of polymetallic crusts or sulfide structures, will likely destroy these ecosystems as the organisms are dependent on the very material that miners are planning to remove to survive. In addition, these organisms are also slow growing and long-lived so they are slow to recover from any physical disturbances.
One of the impacts of deep-sea mining that researchers are most concerned about is the creation of sediment plumes when the tailings from mining are dumped back into the ocean. These tailings are often made-up of fine particles of sediment that remain in the water column instead of settling when pumped back into the ocean. When these sediment clouds form near the ocean floor they increase the turbidity of the water and can clog the filter-feeding apparatus of a variety of benthic organisms thus preventing them from feeding. Depending on a variety of factors these plumes may travel far distances and disturb organisms in a much wider radius than just the area being mined.
Sediment plumes, originating from deep-sea mining activities, can also form near the surface and depending on currents and size can spread over vast areas, impacting zooplankton and light penetration in surface water. As zooplankton are the base of the food-web, any disturbance to them will impact the rest of the food chain.
Noise and Light Pollution
Deep Sea Mining efforts will generate much higher levels of light and noise disturbances than those present in the usually quiet and dark conditions of the deep-sea environments. This is likely to severely impact organisms adapted for these environments. Studies have already demonstrated that anthropogenic noise affects deep sea fish and marine mammals, impacting their ability to communicate and causing behavioral changes and temporary and permanent hearing damage.
As deep-sea organisms are adapted for low light conditions, their eyes are very sensitive and floodlighting by deep sea machines will likely cause extensive and permanent damage. Previous studies have shown that the bright lighting on manned submersibles exploring hydrothermal vents caused permanent retinal damage to deep sea shrimp resulting in behavioral changes such as disruptions to their vertical migration patterns, their ability to detect prey and their ability to communicate.
Although there are benefits of deep-sea mining, there is a lot more research that needs to be conducted before we fully understand the environmental impacts on the incredible ecosystems that make up the deep ocean.