Deep-sea mining refers to the process of retrieving mineral deposits from the part of the ocean that is below 200 meters. Because terrestrial mineral deposits are either depleting or of low grade, interested parties are turning to the deep sea as an alternative source for these minerals. There is also a rising demand for metals used to produce technologies such as smartphones, solar panels, and electric storage batteries has added to this interest.

But deep-sea mining comes with consequences. The process of involves scraping the ocean floor with machines to retrieve deposits, which disturbs ocean-floor ecosystems and puts deep-sea habitats and species at risk. The process also churns up the fine sediment on the ocean floor which creates sediment plumes. This creates turbidity in the water that affects the biological productivity of the plant life in the ocean as it decreases the sunlight available for photosynthesis. Additionally, the noise and light pollution from the mining machines is harmful to species such as tuna, whales, turtles, and sharks.

Deep-sea ecosystems are made up of species that cannot be found anywhere else in the world. Disturbances from deep-sea mining could completely eradicate these unique species. Below, we examine the impact that deep-sea mining has on biodiversity and marine ecosystems.

How Deep-Sea Mining Works

According to the Encyclopedia of Geology, deep-sea mining began in the mid-1960s with a focus on mining manganese nodules in international waters. It began to develop in the 1970s but was deemed as unfavorable by the mining industry in the 1980s. This was partially a result of the decrease in metal prices in the 1980s. More recently, with the demand for mineral deposits increasing and the availability of terrestrial mineral deposits decreasing, both public and private institutions have been more interested in exploring the prospects of deep-sea mining.

The exact process occurs in a way that is similar to strip-mining on land. The matter on the ocean floor is pumped into a ship, then the slurry is loaded onto barges and shipped to onshore processing facilities. The wastewater and leftover debris are then discarded into the ocean. 

There are three main types of deep-sea mining:

1. Polymetallic nodule mining: Polymetallic nodules are found on the surface of the deep sea and are rich in copper, cobalt, nickel, and manganese. These nodules have been identified as being of potentially high economic value, therefore they have been targeted for future mining. However, little is known about the fauna associated with the nodules.
2. Polymetallic sulphide mining: Polymetallic sulphide deposits are found in the deep sea at depths from 500–5000 meters and are formed on tectonic plate boundaries and volcanic provinces. Seawater makes its way through cracks and fissures into the sub-seafloor, is heated, and then dissolves metals from the surrounding rocks. This hot fluid mixes with the cold seawater resulting in the precipitation of metal sulphide minerals which settle on the seafloor. This creates an area on the seafloor that is rich in zinc, lead, and copper.
3. Mining of cobalt-rich ferromanganese crusts: Cobalt-rich ferromanganese crusts are high in metals such as cobalt, manganese and nickel. These crusts are formed on the surfaces of rocks in the deep-sea. They are commonly found on the side of underwater mountains at depths of 800–2500 meters.

Environmental Impacts

Current research indicates that mining activities could have the following environmental impacts on deep-sea ecosystems.

Seafloor Disturbance

The ocean-floor scraping can alter the structure of the seafloor, affecting deep-sea ecosystems, destroying habitats, and eradicating rare species. The deep-sea floor is home to many endemic species, meaning that they can only be found in one geographic region. More information is needed on the impact that deep-sea mining activities has on these species to ensure that they do not become extinct.  

Sediment Plumes

Sediments plumes form on the ocean floor due to silt, clay, and other particles being churned up during the mining process. A study indicates that for an average 10,000 metric tonnes of nodules mined per day, about 40,000 metric tons of sediment will be disturbed. This has a direct impact on the seafloor as it disperses fauna and sediment in the area where the nodules are removed. Additionally, in the areas where the plumes settle, they smother fauna and prevent suspension feeding from happening. These plumes also have potential water-column impacts that could cause harm to pelagic fauna. Also, sediment and water mixes together to create turbidity, which decreases the amount of sunlight that can reach flora, thus delaying photosynthesis.

Light and Noise Pollution

Machines used for deep-sea mining can be very loud and have strong lights used to shine on the seafloor along the mining path. Artificial light can be very damaging for deep-sea species that are not equipped to deal with a high light intensity. Sunlight does not go deeper than 1,000 meters into the ocean, so many deep-sea organisms have partially or completely reduced eyes. Artificial light from mining equipment can cause irreversible damage to these organisms’ eyes. 

Not much research has been done to date on the role of sound in deep-sea ecosystems. However, it is suggested that the loud noise and vibrations from mining equipment could impact these animals’ ability to detect prey, communicate, and navigate.

Regulations

In 1982, the United Nations Convention on the Law of the Sea (UNCLOS) stated that the area of the seabed and its mineral resources that are not in the national jurisdiction of any country are the “common heritage of mankind”. This means all deep-sea mining activities that occur in this area must adhere to the regulations and guidance for exploration activities approved by the International Seabed Authority (ISA). These regulations require that interested parties take the necessary measures to ensure that the marine environment is protected against any negative impacts from mining activities. Additionally, in the zone that countries do have jurisdiction (200 nautical miles beyond its coast) the UNCLOS states that regulations must be no less effective than international rules.

 The ISA administers regulations on prospecting and exploration for the three mineral types in the area (polymetallic nodules, polymetallic sulphides, and cobalt rich ferromanganese crusts). These regulations require interested parties to have their plans for mining approved before they begin any work. In order to gain approval, environmental and oceanographic baseline studies must show that mining activities will not cause serious harm to marine ecosystems. However, experts from the International Union for Conservation of Nature (IUCN) stated in a report published in 2018 that current regulations are not effective as they lack sufficient knowledge of deep-sea ecosystems and the impact that mining activities have on marine life.

Solutions

The most apparent solution to lessen the impact of deep-sea mining is increasing knowledge on deep-sea ecosystems. Comprehensive baseline studies are necessary in order to fully understand these unique environments that are home to some of the world’s rarest species. High-quality environmental impact assessments (EIAs) are also needed to determine the level of environmental impact that mining activities have. The results from the EIAs would aid in the development of regulations that effectively protect marine ecosystems from deep-sea mining activities.

Mitigation techniques are also important when monitoring the potential harmful impacts on deep-sea environments and the recovery of previously mined areas. One study indicates that mitigation measures include avoiding areas of high importance; minimizing impact by creating unmined corridors and relocating animals from sites with activities to sites with no activity; and restoring areas that have been negatively impacted. A final solution would be reducing the demand for mineral deposits from the deep-sea by recycling and reusing products such as smartphones and clean energy technologies.