A marine biologist dives where blue gives way to black

The shining abyss. By Helen Scales. Atlantic Monthly Press; 304 pages; $ 27. Bloomsbury Sigma; £ 16.99

MALL VISITORS only scratch the surface of the ocean – swim from the beach or slice off white hats on a sailboat. In “The Brilliant Abyss,” Helen Scales, a marine biologist whose previous books have explored the shallower parts of the sea, dives deep and revealingly into the realm below 660 feet where the sunny blue begins to give way. place in black.

As Ms. Scales notes, it is often said that we know more about the surface of the Moon, exposed to anyone with a telescope, than about the geography of the seabed, which a dark mantle of water obscures. It is a rugged, complex and moving terrain, subject to earthquakes precipitated by the movement of tectonic plates, and punctuated by seamounts (mountains formed by volcanic activity) and hydrothermal vents that emit sulphurous fluids and burning.

In these dark and cold submarine extremes, and the boiling waters disgorged by the vents, life survives and even thrives. It features sea cucumbers that peel away from their illuminated skins to distract predators, yeti crabs as hairy as their name suggests, fish masked with ultra-black skin that makes them almost invisible, and a sponge that looks like to a glass of frozen milk in the middle – spread. In addition to its role as a climate regulator and carbon sink, the abyss, in its vibrant profusion, invites us to reflect on the possibility of life on other planets.

Less alluring things are lurking there too. Plastic bags and wrappers have been spotted by submersibles in the seven-mile-deep Mariana pit. Nuclear waste, chemicals and oil spills, like that from the Deepwater Horizon platform in 2010, have turned sections of the seabed into toxic dumps. Exploitation adds to the scourge. Orange roughy, a white-fleshed fish that congregates around seamounts (also known, less appetizingly, as slimehead) has been dangerously overfished.

Another threat is an experimental push to harvest nodules from the seabed containing manganese, nickel, cobalt and other metals. According to Ms Scales, the potential damage to the seabed by remote-controlled machinery is analogous to the most toxic mining operation on land. But the income could be huge. A Massachusetts Institute of Technology analysis calculated that a single seabed mine could bring in $ 1 billion a year.

And an ecological case for the initiative can be made. “I’m very uncomfortable when people describe us as deep-sea miners,” says Gerard Barron of DeepGreen Metals, a deep-sea mining company targeting metals used in electric car batteries. “We want to help the world move away from fossil fuels.” Because the long-term impact is unknown, Ms. Scales is skeptical; his argument is convincing, even if his explanation of car batteries is a daunting task. Another marine biologist doubts that mining will be prevented “even if we find unicorns at the bottom of the sea”.

Early European cartographers often used sea snakes to mark unknown depths. Hic sunt dracones– Here be dragons – reads the inscription of unfathomable water on a globe made in 1510. But perhaps the most menacing sea monster of all is man. â– 

This article appeared in the Books and Arts section of the print edition under the title “Beyond the Blue”