We are 50 kilometers off the coast of San Diego in late February, holding station in 1,000 meters of water. Onboard our research vessel, the RV Sally Ride, are eight containers, each as large as a compact car, filled with sediment dredged from the deep Pacific Ocean floor. This morning we mixed the sediment with seawater in a huge tank, and over an hour we pumped the entire contents through a wide discharge hose that extended 60 meters down into the water from the side of the ship.

For six hours we tracked a plume of particles that dispersed down and away from the boat, pulled by ocean currents. A sophisticated array of sensors hanging from the ship allowed us to measure the plume shape and sediment concentration in the water column, the signals getting ever weaker.

Our goal was to obtain ocean data about a pressing issue that could soon greatly impact the ocean: mining the deep seafloor.

After years of contemplation, governments and companies around the world are beginning to explore the deep seabed for valuable minerals, chief among them nickel, copper and cobalt. One type of deposit—fist-sized nodules containing these metals—lies thousands of meters underwater. Robotic collector machines, each one as big as a combine harvester, would crawl along the seabed, sucking up the top sediment layer containing the nodules, kicking up a cloud of sediment in their wake. The collectors would pump the nodules up wide, kilometers-long tubes to large surface vessels. The ships would sift through the material, separating out millions of dense metallic nodules a day, and return the remaining sediment back into the sea, sending a plume downward.

How would all of this activity affect the life on the ocean floor and in the waters above? Our discharge test was an early step toward one part of an answer.

Global demand for metals is rising relentlessly. Some of the higher-grade land-based mines are running low. Several companies, such as Global Sea Mineral Resources (GSR) and UK Seabed Resources, are pursuing deep-sea mining because they think it can be less costly than land-based mining, especially as terrestrial producers are forced to turn to sites that have lower-grade ores that are also harder to extract.

Certain countries that do not have many mineral resources on land, such as Japan and South Korea, want to get into the game by prospecting at sea, where some deposits are vast. In September 2017 the Japan Oil, Gas and Metals National Corporation conducted one of the first large commercial trials. A prototype excavator gathered tons of zinc and other metals from deposits 1,600 meters deep near Okinawa, inside Japan's exclusive economic zone (EEZ)—its national waters. Small island nations and regions, such as Tonga and Cook Islands, which have limited resources to build such an industry themselves, are discussing whether to offer mining rights inside their EEZs to outside investors. And the International Seabed Authority (ISA), which regulates commercial activity in international waters, has issued 28 exploration permits to institutions from 20 countries to sample seafloor minerals.

Scientists are working hard to learn more about potentially damaging effects and what steps could minimize them. Right now governments, industry, the ISA, universities and science organizations are cooperating on shared research ventures akin to ours. Unlike the history of coal, oil, phosphorus and other natural resources, the scientific community has an opportunity to work with all parties to establish effective safeguards before a large extraction industry forms and to determine the relative impacts of sea-based mining versus land-based mining.

Nickel, Copper and Cobalt Rewards

Swedish explorers first discovered ocean mineral deposits a century and a half ago, in the Kara Sea off Siberia. The treasures were confirmed in the 1870s, during the celebrated HMS Challenger expedition that advanced modern oceanography. In the 1970s the CIA planned an elaborate hoax in which an ostensible dive for manganese nodules in the Pacific Ocean would be cover for its attempt to exhume the sunken Soviet submarine K-129. But technological challenges and low mineral prices discouraged actual commercial exploration.

Credit: Dolly Holmes; Source: World Ocean Review 1. published by Maribus, 2010 (world map); International Seabed Authority. Database by S. Claus et al. Flanders Marine Institute. Accessed at www.marineregions.org on November 24, 2016 (inset)

Interest has picked up markedly over the past decade. Increasing global population, urbanization, rising consumption and aggressive development of technologies that depend heavily on certain metals are pushing market forecasts substantially higher. For example, annual global demand for nickel, now around two million metric tons, is estimated to rise 50 percent by 2030. Around 76 million metric tons exist in land-based reserves. Roughly the same amount, in the form of nodules, lies on the seafloor within the Clarion-Clipperton Fracture Zone (CCFZ) alone, an elongated abyssal plain stretching from Hawaii to the Baja California Peninsula. The story for cobalt is similar: land reserves of about seven million metric tons are matched or even exceeded by nodules in the zone.

Three principal forms of deposits are promising. One comprises active and inactive hydrothermal vents—fissures opened by volcanic activity that spew hot material along the boundaries of tectonic plates. These so-called seafloor massive sulfides are rich local deposits of minerals such as copper, zinc, lead and gold. Papua New Guinea has granted Canadian firm Nautilus Minerals a license to extract these sulfides at an inactive site known as Solwara 1 inside its EEZ. The ISA has granted seven sulfide exploration contracts at inactive sites in international waters. Scientists have called for a mining moratorium at active sites because of their unique ecosystems.

A second type of deposit, cobalt crusts, forms on the hard rock summits and flanks of seamounts, as metals naturally precipitate out of the seawater. Such crusts grow very slowly, a few millimeters every million years, typically reaching thicknesses of five to 10 centimeters. In addition to cobalt, they contain nickel and other desirable metals. Although the ISA has issued four exploration licenses for the western Pacific Ocean, mining of cobalt crusts is challenging because it is difficult to strip off the crusts from underlying rock and because the rock faces are typically steep and hard to negotiate underwater.

The majority of deep-sea mining ventures target deposits of polymetallic “manganese” nodules. (The remainder of this article addresses just this kind of mining.) The nodules are strewn across the seafloor or are partially buried in the sediment across many large areas. They form at depths of several thousand meters as metals precipitate out of seawater around a piece of detritus, forming a kernel that grows in diameter at about one centimeter every million years.

The ISA has granted 16 nodule exploration licenses in the CCFZ. Although composition varies, a typical nodule there contains around 3 percent by weight of nickel, copper and cobalt, which are the real prizes. About 25 percent is manganese, which if mined at scale would greatly increase global supply. The rest is mostly hardened material of no economic interest.

Nodules are the New Gold

Surveying a potential site takes months with ship-based instruments, autonomous underwater vehicles and box-shaped collectors lowered from the ship to gather samples. Because the areas being explored are so large, the test samples are statistically extrapolated across the entire field. Prospectors consider a mining site economically viable if the nodule concentration exceeds about 10 kilograms per square meter, the nodules are covered by little or no sediment so they are easy to pick up, and the seafloor's slope is less than 10 percent, making it manageable for the collector machines, which typically crawl on heavy rolling tracks.

The centerpiece of a mining operation would be the collector vehicle, powered by an electric umbilical cable from the ship. It would scour the seabed, covering about 50 kilometers a day, most likely back and forth in a kilometer-scale grid pattern across a field of nodules. Autonomous submersible vehicles would help guide it along and monitor the surrounding environment.

Critical metals contained in manganese nodules are hauled up from the Pacific Ocean seafloor during a sampling operation by Nautilus Minerals. Credit: Nautilus Minerals

As the collector sucks or scoops up the nodules and accompanying sediment, it would perform some rough separations of nodules, expelling the unwanted sediment in a cloud behind it. A long hose, with a series of pumps, would send the nodule slurry up to the operations ship—a riser system based on established technology used by the oil, gas and dredging industries. The vessel would separate nodules, sending unwanted sediment back down into the sea through a discharge hose. Large cargo vessels would take the nodules to a processing plant on land, which would extract the desired metals.

Economic viability studies indicate that to turn a profit, companies would need to collect three million metric tons of dry nodules a year, yielding about 37,000 metric tons of nickel, 32,000 metric tons of copper, 6,000 metric tons of cobalt and 750,000 metric tons of manganese.

Effects on Living Organisms

The ISA was established under the United Nations Convention on the Law of the Sea (UNCLOS), which requires that signatory nations take all measures to protect the marine environment. The ISA grants exploration licenses to tracts that are 150,000 square kilometers. Because those who ratified or acceded to UNCLOS—167 nations and the European Union—view the international seabed as a resource for the “common heritage of mankind,” a company or organization that wants to mine must be sponsored by a country that has ratified the convention. After surveying is done, the company splits a parcel into two halves, and the ISA decides which half to reserve for a developing country for possible exploitation.

Studies indicate that of a company's 75,000-square-kilometer parcel, it is likely to find about 10,000 square kilometers (about 0.2 percent of the CCFZ) economically viable to mine. The collector would remove the top 10 to 15 centimeters of the seafloor and compact the seabed in this region. A varied array of life at a scale of 50 microns or larger live on the nodules or in the sediment. Most of these creatures will die from the scouring or be smothered by the sediment cloud as it settles.

Smaller microorganisms such as bacteria account for the rest of the biomass. It is unclear how well these tiny species will fare. They will be kicked up with the sediment and settle back down many kilometers away. Those that rely on the nodules as a substrate for their existence will likely do poorly. Given that nodules take millions of years to form and that biological communities away from hydrothermal vents in the deep ocean are very slow to develop, harvested regions are unlikely to recover on any human timescale. Nearly 30 years ago German researchers used a sledge to dredge simulated mining tracks in the seabed 4,100 meters down in the Peru Basin. When investigators revisited them in 2015, the tracks looked as if they had just been created.

The impact of the collector's sediment plumes is another concern. Weak background currents in the deep ocean, which move at several centimeters a second, could carry sediment particles many kilometers away from where a collector is operating. Much of the sediment is fine, around 0.02 millimeter in diameter, with a typical settling speed of around one millimeter per second. Such sediment from collector plumes reaching 10 meters high or so in the background currents could travel around 10 kilometers away from the mining site.

This estimate may be oversimplified because fine sediments tend to aggregate into larger flocs that would settle faster than individual particles would, thereby potentially limiting the horizontal extent of plumes. The background sedimentation rate in the deep ocean is so low, however—on the order of one millimeter per 1,000 years—that biologists think trace amounts of sediment emitted by a collector could smother seafloor life even farther away. Compacting the seabed is also a concern. Studying the effects of occasional abyssal storms that scour sediment from the deep seafloor could provide valuable insights.

Estimating the impact of sediment plumes from the ship on the ocean environment and ecology is challenging. Upper ocean currents are faster, and there is more turbulence. The discharge hose could extend hundreds of meters down. The sediment plume coming out of it would take a roughly conical shape, tens of meters in scale, that currents would dilute, twist and transport several kilometers a day. In our February experiment off San Diego, we tracked the discharge plume with a variety of instruments. Ocean currents made it sinuous, and tendrils formed that intertwined. A towed, underwater device took samples from the tendrils. We will need a month or two to analyze all the data and figure out the key information, including what the sediment concentrations were close to and far from the hose.

Meanwhile researchers are trying to determine the extent to which the loss of life in a mining zone would affect local biological systems, as well as adjacent deep-sea communities and even those many kilometers away. In the CCFZ, the ISA has designated nine large protected regions and is also developing protocols for establishing preservation zones within each license area. Experts will monitor these and other places to see what impacts arise.

Mining Land vs. Sea

It is important to weigh the environmental pros and cons of deep-sea mining with mining on land. In the Democratic Republic of the Congo, for example, which supplies around 60 percent of the world's cobalt, terrestrial mining causes deforestation and water and air pollution—and also involves child labor. In some countries, companies that mine for nickel are exhausting deposits that are relatively easy to access, so they are moving into deposits that are harder to extract, requiring more energy and chemical processing and thereby leading to greater environmental impact.

Processing facilities for nodules brought onshore from seabed mining will have land consequences as well. If only 30 percent of a nodule is desirable metals, 70 percent is waste, typically a slurry. Land miners often send this slurry back down the hole they have created. Slurry from millions of ocean nodules will be new material that has to go somewhere. On the upside, collectors and ships can leave an area and move to a new one; surface-mining infrastructure, once built, is hard to remove.

To reduce extraction and environmental impacts, it is vital that society develop effective global recycling programs. But recycling alone cannot keep up with rising demand. Today it is difficult to say whether seabed mining will be environmentally worse or better than the equivalent degree of land-based mining.

Of course, regulation will affect that outcome. The ISA, based in Kingston, Jamaica, regulates more than half of the planet's ocean floor—in international waters, also known simply as the Area. The ISA, which has no ships to inspect operations, has shared this responsibility with sponsor nations. It could revoke a company or country's license, suspend operations or impose a fine if it was determined that mining in a region was exceeding environmental impact standards.

The U.N. has 14 member states that have signed UNCLOS but have not ratified it—most notably the U.S.—and another 15 member states that have not signed it. These 29 nations could ostensibly try to mine in international waters and flout ISA statutes. The ISA would have to appeal to global politics to settle this kind of situation.

The organization has released draft exploitation regulations for the Area. They are intended to eventually cover everything from how the authority approves or rejects exploration and exploitation contracts to the obligations of contractors and the protection and conservation of the marine environment. The ISA expects to have exploitation regulations in place by 2020. Countries will have to write their own regulations for land-based nodule-processing facilities.

Also intriguing is what happens within countries' EEZs. These national waters account for more than one third of the world's oceans. Some countries do not have “deep seas” within 200 nautical miles (370 kilometers) of shore. But others do, particularly island nations in the Pacific. A few countries, such as Palau, have simply said no to any seabed mining. Other nations and regions, including Tonga, Kiribati and the Cook Islands, are developing regulations as they seek industrial and international partners. The Cook Islands has signed a contract with Ocean Minerals, based in the U.S., that gives the company a priority right to apply to explore 23,000 square kilometers of the islands' waters for cobalt-rich nodules.

Such actions show that seabed mining is poised to become a reality. Given the growing economic and strategic interest, some nations may start exploratory mining in the next five to 10 years. As noted, Japan has already begun.

A worthwhile path forward is for all interested parties to cooperate, as they have done so far, with small-scale industrial testing proceeding hand-in-hand with much needed scientific research. Indeed, a great deal of what is known about ecosystems and resources in the CCFZ has come from contractor-related studies. Our expedition from San Diego, for example, was a joint program funded by the Massachusetts Institute of Technology and the Scripps Institution of Oceanography, in collaboration with the ISA, the U.S. Geological Survey and GSR. In 2019 Europe's JPI Oceans program will conduct a study with the ISA and GSR in the CCFZ.

Some guidelines and standards for commercial operations might be adapted from existing industries, and others might be wholly new. If the parties can continue to work together, deep-sea mining could set a global benchmark. Historically, regulations have lagged behind industrial extraction—think about fracking—forcing regulators and citizens to try to catch up. As Conn Nugent of Pew Charitable Trusts says, “There is an opportunity to write the rule book that will govern an extractive activity before it begins.”