The Deep Sea Is Earth’s Last Mystery

Some of the most optimistic developments of the 20th century remain largely unknown. Three once-inaccessible regions were not only reached for the first time, but even more astonishingly, ended up amicably regulated by a consortium of nations and made into lasting international commons. The legal structures governing Antarctica and outer space were worked out in the 1960s, and the treaty for the international seabed was ratified by the mid-90s. These are not small places. Antarctica and the deep sea alone constitute more than 50 percent of Earth’s surface. The moon and Mars together have about 60 percent of the surface area of Earth.

In any previous century, proposing property law for Mars would’ve been the kind of thing that one yells on the street between discussions on regulating werewolf populations and usage of the philosopher’s stone. By the middle of the last century, however, Antarctica, the seafloor, and outer space were accessible, and all three looked like potential sources of a wealth of minerals and land, and with it, the danger of a 19th-century-style territorial scramble.

The Deepest Map: The High-Stakes Race to Chart the World’s Oceans, Laura Trethewey, HarperCollins, 304 pp., $32, July 2023.

As it turned out, there was little conflict—and less wealth. Was this due to the enlightened liberalism and environmentalism of the 20th century? Perhaps, but one reason that it was possible to convert an area larger than Earth’s surface to a commons was that all of these places are awful. They are hell on equipment and require human visitors to spend most of their time in purpose-built mechanical bubbles lest they die.

Yet today, while space remains extravagantly expensive to access and Antarctic law forbids the exploitation of resources, the deep seabed is beginning to look like a promising source of metals in a tech-hungry world. Under the rules of the International Seabed Authority, it will soon be possible for private companies backed by states to exploit ocean-bottom resources in international waters.

But there’s a problem: Whereas the moon, Mars, and Antarctica are mapped in exquisite detail, the seabed, enfolded in miles-deep water, remains largely unknown. If, indeed, deep seabed mining happens, empty swaths on the map aren’t just a danger for miners, but for the undiscovered ecosystems that have flourished deep underwater since well before the first human was born.

This is the stage on which the drama of The Deepest Map: The High-Stakes Race to Chart the World’s Oceans, by journalist Laura Trethewey, takes place. We are introduced to the modern effort to use advanced sonar on the seafloor by following Cassie Bongiovanni, a young scientist who takes the job of mapper aboard the Pressure Drop. The mission is paid for by an eccentric Texas millionaire, Victor Vescovo, who wishes to send himself to the “Five Deeps”—the deepest points in each of the five oceans.

Although Vescovo is convinced to contribute the resulting data to the ocean-mapping project known as Seabed 2030, that isn’t why Cassie was hired. She’s there because even today, only around 25 percent of the seafloor is mapped and only about 1 percent has been visited by ROVs. In an undersea world where some depth measurements come from soundings more than a century old, diligent eccentric millionaires need to do some sonar scanning to make sure their deeps are indeed the deepest.

The results are casually shocking, as are Trethewey’s findings in her interviews and research. This is not one of those pop science books where the reader yawns through rehashed stories and familiar factoids. The research is extensive, the topics are diverse, and we are taken down forgotten alleys of knowledge—such as the plight of midcentury women oceanographers, including Roberta Eike, a graduate student conducting research in the 1950s, who was literally spanked by her supervisor for stowing away on an all-male research cruise.

There are wondrous things here, too. The sea might seem like a vast and empty stage, but it has its own dramas. There is the massive movement of undersea life to feed at night and hide from predators by day—an uncoordinated action so enormous that sonar workers in the Second World War called it the “false bottom.” There are countless undiscovered shipwrecks, cities of octopodes, regular discoveries of new species in sea-bottom sampling, massive newly located coral reefs, uncharted islands, and previously unknown fish colonies.

In one of the most riveting chapters, we learn of long-lost human settlements off the coast of Florida, the remains of which still exist submerged underwater, relics from an era when the seas were lower. As Shawn Joy, an archaeologist, related to the author, “…the farther offshore you go, the further back in time you travel.”

At the heart of all this wonder is an ethical paradox—demystifying the seafloor simultaneously tells us what we need to protect and what we might one day exploit. Often, they are one and the same. The focus of potential sea-miners is polymetallic nodules—little potato-shaped accretions on the seafloor, made of valuable metals. But those very nodules may be home to many of the larger life forms living in the abyssal plains—the great stretches of flat terrain in the deep sea.

Also tempting are the black smokers—underwater vents discovered only in the 1970s. These ancient structures are surrounded by exotic chemosynthetic organisms, and they may have already been where life on Earth first arose. They have also accumulated rare earth elements over time, many of which are used as inputs in electric vehicles and other clean technologies. Thus, they present an environmental ethics dilemma: Must we destroy the cradle of life to preserve the cradle of humanity?

Answering this question is the one serious flaw in The Deepest Map. While the author does an excellent job—and often an exhilarating job—telling us what we have and why it is precious, she leaves us with little sense of what the result will be if we do not exploit these resources. Some of the most interesting passages concern Gerard Barron of the Metals Company, a mining start-up focused on the seafloor’s polymetallic nodules, who explicitly talks about how deep-sea mining would benefit clean technology. In his view, the damage to these environments is minor when compared to the planetary benefits of their resources. Trethewey is skeptical of this view, but her counterarguments here and throughout are thin compared to the depth of research elsewhere in the book.

We sympathize with the view that everything beautiful should be protected, but this is a world of trade-offs, and a hot and hungry world at that. The value of these minerals is not merely a concern for rich consumption-driven nations. Small island communities are sometimes the most conflicted of all: One delegate to the International Seabed Authority from Micronesia informed the author that while island nations often share political views, sea-mining divides them. Exploiting the sea bottom could disrupt the fisheries they depend on or might simply fail and squander precious capital, but it could also produce hundreds of millions of dollars every year—life changing wealth for tourism-dependent islands devastated by the COVID-19 pandemic.

And while Trethewey treats us to solid scientific and historical information on the deep sea and those who map it, when it comes time to weigh difficult choices, the book becomes vague, almost mystical—quoting Thoreau and urging that “Inner soul-searching must accompany outward exploration, or else we fall into a trap of ticking off new frontiers like an endless shopping list.”

This is unfortunate, because the author had the ability and the space for more analysis. Her research work is excellent, and much ink is spilled on fairly uneventful narrative portions. Bongiovanni, the earnest young scientist, and Vescovo, a millionaire who often speaks in platitudes, are neither as interesting as Trethewey’s own adventures in history and archaeology, nor as compelling as the big questions about exploitation in undersea ecosystems.

If the book were entirely a catalog of wonders and stories, it would be almost perfect. But, especially in the second half, there are attempts to reckon with the ethical and political issues surrounding seabed mining. Here, we would have liked to see the author go, well, a bit deeper.