In 2018, Brazilian and British scientists have been exploring the seafloor round a volcanic plateau often called the Rio Grande Rise after they noticed rocks that seemed like they belonged on dry land.Watching video relayed from their remotely operated submersible 650 meters (2,100 toes) under the floor, uncommon pink clay layers caught their consideration. “You simply do not discover pink clay on the seabed,” stated Bramley Murton, a marine geologist from the Nationwide Oceanographic Centre in Southampton, U.Ok., who was on the expedition. “The deposits seemed like tropical soils,” he defined.In a current examine, the group confirmed that the clay’s distinctive mineral make-up might have shaped solely by open-air weathering in tropical warmth and humidity. It is the most recent in a string of discoveries hinting that this patch of ocean, 1,200 kilometers (750 miles) from Brazil’s coast, was as soon as an island.Volcanic originsResearchers captured pictures and samples of the seabed across the Rio Grande Rise with a remotely operated car. Purple clay, hinting on the space’s earlier existence as an island, pokes out beneath the black basaltic lava. (Picture credit score: Luigi Jovane)”Think about a lush tropical island slipping beneath the waves and mendacity frozen in time. That is what we have uncovered,” stated Murton, who coauthored the examine. He and colleagues assume the island would have been related in dimension to Iceland (a couple of fifth of the Rio Grande Rise’s whole space).The origins of the Rio Grande Rise return 80 million years. An infinite mantle plume sat beneath the South Atlantic’s mid-ocean ridge, inflicting a burst of intense volcanism; the ensuing rise “began life as a Cretaceous model of Iceland” nearer to the mid-ocean ridge than what’s now South America, Murton stated. Step by step, as volcanic exercise subdued, the volcanic plateau drifted west throughout the Atlantic and sunk beneath the waves.However beginning round 40 million years in the past, the mantle plume had one final gasp of volcanism, this time remoted to the western portion of the rise. And it is on this space that the researchers discovered the pink clays, sandwiched between lavas recognized to be about 45 million years outdated.”That is an excellent outcome,” stated Luigi Jovane, a marine geologist from the College of São Paulo and coauthor of the examine. “The pink clays are conclusive proof that this was as soon as an island.” Jovane has been main investigations within the Rio Grande Rise for greater than a decade.Underwater ExplorationThe analysis is the end result of two scientific expeditions to the rise in 2018. The primary, aboard the Brazilian analysis vessel Alpha Crucis, mapped the rise’s underwater terrain utilizing sonar. That venture was initially geared toward characterizing mineral-rich ferromanganese crusts recognized to happen on the seafloor of the rise.The researchers’ mapping revealed a steep-sided, 30-kilometer-long (20-mile-long) canyon bisecting the rise — the Cruzeiro do Sul Rift — in addition to historic seashore terraces, wave-cut platforms, and drowned waterfalls.Eight months later, the group returned aboard the Nationwide Oceanography Centre’s RRS Discovery. That vessel is provided with a remotely operated car (ROV), which allowed them to seize footage of rocks uncovered within the steep-sided canyon partitions. The ROV additionally has a robotic arm for gathering samples.Most investigations of seabed geology depend on sonar mapping and dredging for rock samples, stated Tony Watts, a marine geologist from the College of Oxford who was not concerned within the examine. However “by utilizing an ROV, [the researchers] may very well be extra assured in regards to the location and context of the pink beds.”This bathymetric map reveals seafloor options alongside the Brazilian meridional continental margin, together with the Rio Grande Rise. (Picture credit score: Ana Alberoni, modified from Alberoni et al., 2019)Armed with a pattern of the pink clay, the researchers measured its mineral composition again within the lab. They discovered that it largely contained a sort of clay mineral known as kaolinite, which dominates tropical soils as a result of it’s immune to excessive chemical weathering.”These pink clays are precisely the identical, chemically and mineralogically, because the pink earth or terra roxa we discover throughout Brazil,” Jovane stated. “We’re assured that they characterize the in situ, weathered higher surfaces of the lavas.””It is a strong dataset,” stated Watts, who agreed with the group’s interpretation that this space was as soon as above sea degree. He added that the analysis has vital implications for understanding the magmatic and subsidence historical past of the rise.Proof collected within the Eighties, together with drill cores containing shallow-water microfossils, had indicated the western a part of the rise was uplifted in the course of the Eocene, Murton stated. However “nobody has discovered convincing proof for subaerial volcanism and publicity of the western rise till now.”Coveted mineralsThe Rio Grande Rise is extra than simply scientifically fascinating. It additionally has potential financial worth owing to its ferromanganese crusts. In December 2018, the Brazilian authorities utilized to the United Nations to increase its maritime borders to incorporate the Rio Grande Rise.The rise is positioned in worldwide waters and is effectively past Brazil’s 370-kilometer-wide (200-nautical-mile extensive) unique financial zone — the place coastal nations have sovereignty over seabed sources. To qualify for an extension, Brazil must show that the rise has the identical geological traits because the nation.The rise’s newfound standing would possibly assist bolster that ongoing declare. “The Rio Grande Rise and the continent have the identical soil and local weather,” defined Jovane. “In that sense there’s a direct relationship between the 2.”Jovane stated Brazil must show not solely that it has an accurate declare to the Rio Grande Rise however that it might mine the realm sustainably. At present, Brazil has laws for mining solely on land, and there may be nonetheless no laws for seabed mining in worldwide waters.This text was initially revealed on Eos.org.