Cut rock samples from the Rio Grande Rise show Fe-Mn crusts (black and gray) growing on various types of iron-rich substrate rocks (pale to dark brown). Photo credit: Kira Mizell, USGS.

A lost continent rich in cobalt crusts could create a challenging precedent for mineral extraction in the high seas

The Rio Grande Rise is an almost completely unstudied, geologically intriguing, ecologically mysterious, potential lost continent in the deep south Atlantic. And it also hosts dense cobalt-rich crusts.

The Rio Grande Rise is a region of deep-ocean seamounts roughly the area of Iceland in the southwestern Atlantic. It lies west of the Mid-Atlantic Ridge off the coast of South America and near Brazil’s island territories. As the largest oceanic feature on the South American plate, it straddles two microplates. And yet, like much of the southern Atlantic deep sea, it is relatively under sampled.

Almost nothing is known about the ecology or biodiversity of the Rio Grande Rise.

A recent study attempts to rectify that knowledge gap and provide insight into how deep-sea mining for cobalt-rich crusts will impact these almost completely unknown ecosystems. The Rio Grande Rise is inhabited by a diverse collection of predominantly sessile organisms that grow slowly on the even-slower accumulating crusts. Surprisingly, the Rise appears relatively free of pollution or human disturbance, likely due to the low productivity of the ocean above. The seamounts that rise from a 6000-meter basement to just below the surface provide the perfect conditions for the formation of cobalt-rich ferromanganese crusts.

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