Project set to investigate origins of mineral deposits on floor of Atlantic

Researchers from Brazil and the UK will use underwater robotic vehicles to discover how polymetallic deposits formed on the ocean floor millions of years ago. The project is supported by FAPESP.

By Elton Alisson

Agência FAPESP – Deposits of various metals can be found in some areas of the ocean bottom at water depths as great as 5,000 m. The most frequent are manganese nodules with diameters of 10-20 cm. They cover much of the deep sea floor in the surface layer of sediment and contain iron, copper, nickel and cobalt as well as manganese.

Polymetallic crusts have been found in slightly shallower water at depths in the range of 500-1,500 m. Encrusting hard volcanic rocks on the slopes of seamounts, they are rich in cobalt and contain less manganese, copper and nickel than nodules.

An international consortium of scientists from universities and research institutions in Brazil and the United Kingdom plans to find out how these polymetallic deposits formed in the Atlantic millions of years ago. One of the project’s focal points is investigating the environmental conditions that favored their formation and growth.

The five-year project is part of Security of Supply of Mineral Resources (SoS Minerals), an interdisciplinary research program funded by the Natural Environment Research Council (NERC) and the Engineering & Physical Sciences Research Council (EPSRC), and supported by FAPESP under a cooperation agreement with Research Councils UK (RCUK).

“The purpose of the project is to understand the environmental factors that conditioned the occurrence of these polymetallic deposits on seamounts and abyssal plains of the North and South Atlantic,” said Frederico Pereira Brandini, Full Professor at the University of São Paulo and Director of its Oceanographic Institute (IO-USP), in an interview with Agência FAPESP.

According to Brandini, who is the lead investigator on the Brazilian side, the researchers will study the Rio Grande Elevation, a chain of submerged mountains approximately 1,300 km off the coast of Rio Grande do Sul, Brazil’s southernmost state, and the Madeira abyssal plain in the North Atlantic. Both areas are known to contain polymetallic nodules and crusts.

Four scientific expeditions are planned to study these two areas. One will be conducted by researchers from the UK to investigate the Madeira abyssal plain. The other three expeditions, each of which is expected to last about a month, will be led by Brazilian researchers, who will study the Rio Grande Elevation and adjacent basins at similar latitudes to those of the expedition to Madeira.

“The idea is to compare the processes that control the formation and composition of polymetallic deposits in these two contrasting ocean environments,” said Luigi Jovane, a professor at IO-USP and a participant in the project.

Submarine robots

The Brazilian scientists will survey abyssal plains in the South Atlantic on board the Alpha Crucis, an oceanographic research vessel bought by FAPESP for IO-USP in 2012.

To study the ocean bed environments in which the polymetallic deposits are located, they will use underwater robotic vehicles (URVs) developed for UK universities and research institutions, and for oil and mining companies.

Designed by NERC’s National Oceanography Center (NOC) at Southampton in the UK, the unmanned URVs that will be brought to Brazil for use in the project can dive to depths of up to 6,500 m.

The URVs are equipped with video cameras, sensors and scientific instruments. They also have manipulator “arms” that can collect samples and pick up delicate objects with precision. The benthic experiments to be performed with these devices could never be attempted by human divers because of the immense water pressure at these depths.

“It will be the first study ever done in Brazil using a technology we don’t yet have,” Brandini said. “The project will enable participating Brazilian researchers and students to make contact with this technology and learn to use it.”

According to the researchers, one of the advantages of using URVs for the project is that they will let scientists see the areas from which polymetallic deposits will be sampled while still intact, transmitting real-time images to the research vessel via fiber optic cables.

In addition, they will help scientists perform complex experiments on the polymetallic deposits themselves, preserving the environmental conditions and minimizing the damage caused by extraction of samples to be taken to the surface.

“By using URVs, we intend to preserve the environmental conditions in which the polymetallic deposits are found,” Jovane said. “The biotic components, such as microorganisms, contained in the nodules and crusts in this extreme environment will be studied by Paulo Sumida, a professor at IO-USP, and his group.”

Multidisciplinary project

According to Jovane, several hypotheses could explain the formation of polymetallic deposits on the seafloor. In particular, there are two opposite theories that generate substantial ambiguity about the origins of the various types of deposit.

One of these theories, which will be studied during the project by Vivian Pellizari, a professor at IO-USP, and her group, is that polymetallic nodule formation is mediated by microorganisms. Biomineralization, a process whereby organisms produce minerals, led to the formation of micromodules, which increased in size over time as more minerals resulting from biogenic processes were deposited.

The other theory is that the deposits emerged from elements that existed in the soil of the ocean floor itself. “No one knows which hypothesis will be proved correct,” Jovane said. “Both of them could be right.”

The multidisciplinary project will involve researchers in geology, geophysics, geochemistry, physical oceanography, biology and microbiology. It will look for evidence to support both hypotheses, as well as studying how the areas’ microtopography, ocean currents and water column composition contributed to the genesis, growth and content of these polymetallic deposits, Jovane explained.

According to the researchers, rising and falling water flow rates carve out channels as deep-sea currents pass over or around seamounts. Understanding all this will also play a key role in their investigation of how polymetallic nodules and crusts are formed.

For this reason, during the project Brandini’s group and another group led by Ilson da Silveira, also Full Professor at IO-USP, will study the benthic boundary layer, the layer of water moving over the sediment at the bottom of the sea, as well as deep-sea vertical flows of remineralized organic matter.

“We also want to understand how polymetallic deposits evolved during the geological history of the ocean floor and how variations in ocean temperatures relate to the growth of these crusts and nodules,” Jovane said.

Because of economic interest in the mineral content of submarine polymetallic deposits and in the many potential industrial and technological applications, the researchers also plan to evaluate the environmental impact of extraction considering different economic, technological and geopolitical scenarios.

Deep-sea biota and seabed communities are fragile, grow slowly, take a long time to reach sexual maturity and display low fertility, so sustainable use of these resources requires the creation of areas in which biodiversity will not be affected, in accordance with guidelines issued by the International Seabed Authority (ISA), an intergovernmental body that regulates mineral exploration and extraction in international deep seabed areas beyond the limits of national jurisdiction, Jovane explained. The ISA was established by the UN Law of the Sea Convention.

“Alexander Turra, also a professor at IO-USP, will coordinate discussions among different interest groups in partnership with the Brazilian government to draft proposals for the sustainable use of these resources,” Jovane said.

For example, deep-sea polymetallic crusts contain large amounts of tellurium, a critical ingredient of thin-film photovoltaic cells. Tellurium is extremely rare in the Earth’s continental crust.

The polymetallic nodules found on the ocean floor contain 20 times more nickel than deposits on dry land. Nickel is an important mineral used in cellphone, notebook and tablet batteries, among many other applications.

“Hence all the economic interest in extracting the minerals found in polymetallic deposits,” Jovane said. “We want to understand why they’re abundant in some areas of the oceans and not in others.”

According to one estimate cited by the ISA, approximately 6.35 million square km, or 1.7% of the ocean floor, is covered by cobalt-rich crusts, translating to some 1 billion metric tons of cobalt.

“The results of this project could help Brazil exploit the mineral resources found in international waters,” Jovane said. “To stake such a deep-sea mining claim, Brazil must demarcate the polymetallic deposits that are located in its area of interest and that it is capable of developing.”