This part of the South Atlantic seafloor is rich in cobalt, nickel and lithium, as well as tellurium and various rare earth elements critical for energy conversion. Researchers plan to continue studying its natural processes.

A study by scientists from the University of São Paulo (USP) in Brazil has shown that the Rio Grande Rise (RGR), a submerged basalt plateau and series of seamounts in the southern Atlantic Ocean, is located about 1,200 km off the coast of Brazil. Once a giant tropical island Filled with minerals and lush vegetation, this island’s history dates back to the formation of sedimentary deposits 45 to 40 million years ago.

An article describing the results of the study, covering nearly ten years of research, was published in the journal Scientific Reports New insights into the geology of the RGR, which is approximately the size of Spain.

The researchers analyzed bottom sediment samples excavated at a depth of approximately 650 m in the western part of the RGR and characterized their mineralogical, geochemical and magnetic properties. The samples contained mostly red clay and a variety of minerals typical of tropical volcanic alteration, such as kaolinite, magnetite, oxidized magnetite, hematite, and goethite.

The group proposed that RGR was once an island, based on discoveries made during scientific expeditions in the region where they collected the sample described in the paper in 2018. They traveled on the Royal Research Ship (RRS) DiscoveryOperated by the UK National Oceanography Center (NOC) Alpha CrucisUSP oceanographic research vessel. The expeditions were part of a thematic project supported by FAPESP. The researchers were from the US Institute of Oceanography (IO) and the University of Southampton in the UK.

“Our research and analysis allowed us to determine that this is indeed an island, and it is currently being discussed whether this area can be included in Brazil’s legally recognized continental shelf. Geologically, we found that the clay was formed after the last volcanic activity 45 million years ago. That means its formation took place 30-40 million years ago.” “And it probably formed as a result of these tropical conditions,” Luigi Iovane, the paper’s final author and IO-USP professor, told FAPESP.

According to Giovanna, principal investigator of the FAPESP-funded project, the fact that the study involved an interdisciplinary team contributed to the results. “We have a top-quality team of experts in geology, geochemistry, biology, hydrodynamics, environmental impact assessment, new energies, psychology and law. All of this accumulated science can be used to improve our understanding of the RGR and prospective research of the region without impacting local system synergies. We need to analyze the sustainability and impact of this mining to know whether resources can be sustainably extracted from the seabed. For example, the ecosystem services the ocean provides there have not been studied in detail. When you intervene in an area, you need to know how it will affect animals, fungi and corals and understand your impact on cumulative processes,” Jovan said.

The paper’s first author, Prieshu Srivastava, now a professor at the University of Mumbai in India, also received support from FAPESP through two projects (19/11364-0 and 22/02479-0).

Giovane has led the production of four more papers on volcanic rock and ferromanganese crust samples from RGR until 2023. Published articles Frontiers in Marine Sciences, Journal of Materials Research and Technology, Geochemistry And Marine Geology).

Exploration of the sea floor

The scientists focused on the western part of the RGR, which they reconstructed using high-resolution bathymetric mapping that showed plateaus covered with sediments and separated by a rift more than 600 meters deep. vehicle (ROV) from Discovery for creating maps, videos and sonar surveys.

The UAV can cover a predetermined area by diving to the seabed for a maximum of 12 hours. The ROV connects to the ship via a cable as it moves, creating high-resolution images and collecting rock and organism samples using a robotic arm. “No one in Brazil has an AUV or ROV, so our partnership with our NOC colleagues in the UK was essential, but the research is 100% Brazilian,” Jovan said.

The presence of tropical soil among the lava flows the researchers discovered suggests that the rocks must have been exposed to open air in a hot, humid climate in a region with active volcanoes less than 40 million years ago. The soil resembles “red soil” (terracottaAccording to Jovan, it can be found in many parts of the state of São Paulo.

The most common measure of rock weathering, known as the chemical alteration index (CIA), was 93 for red clay. Most alkaline rocks have a CIA value of less than 50. This high value indicates that it was caused by extreme weathering of lava flows and volcanic rocks during the Eocene (second period of the Paleogene period) between 56 and 34 million years ago. Despite the sudden climate changes that occurred with Australia’s rapid separation from Antarctica, temperatures contributed positively to the development of tropical forests. Open erosion was accompanied by thermal subsidence and submergence in the late Eocene and early Oligocene, 35 to 25 million years ago.

RGR has been intensively researched in recent years due to its economic potential. It is in international waters and therefore managed by the International Seabed Authority (ISA). In December 2018, the Brazilian government applied to expand its continental shelf to include the RGR, which is well beyond the 200 nautical mile limit set for all countries by the United Nations Convention on the Law of the Sea (UNCLOS).

RGR has identified areas rich in cobalt, nickel and lithium, as well as tellurium and other rare earth elements, which are critical to the transition from fossil fuels to renewable energy, one of the main drivers of global warming.

“It is important to understand the ecosystem services and other natural processes operating in the RGR,” Jovan said. “Only this information can allow us to assess the impact on the environment and calculate the mitigation and compensation measures needed to protect it if economic development is allowed.”