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Susan Casey, veteran journalist of the life aquatic, explores the history and wonder of the subterranean ocean world in ‘The Underworld’


Why do we focus so narrowly on the stars when there are awe-inspiring wonders right in our own planet’s watery depths? Susan Casey may radically change all that. The best-selling author has chronicled mind-bending aquatic adventures before, tracking giant swells (”The Wave”) and sharks (”The Devil’s Teeth”). Now, in “The Underworld,” she dives into the subterranean ocean world — the waters below 600 feet deep — traversing the planet to talk with marine biologists, geologists, and oceanographers, and going on dives herself in order to experience the unknown realm of the deep that “glittered in my imagination like a distant galaxy. What kind of place was it? What was it like to be there? What would you see if you went?


Casey’s story is irresistibly personal, as she first tells us how the ocean won her heart when she threw a chunk of hot dog into one of the Toronto lakes, and a foot-long fish lunged for the snack. A serious competitive swimmer, free diver, and scuba diver, she soon was hooked on exploring and revealing the secrets of the ocean’s four levels: twilight, midnight, abyssal, and the hadal zone, an astounding 36,000 feet down.

She also recounts how, throughout history, others have been similarly mesmerized, confounded, or even terrified by the watery deep. In 1539, the Carta Marina, a map of the North Atlantic, North Sea, and Norwegian Sea regions, was made by a Catholic scholar priest who clearly was afraid of the ocean, because he illustrated it with supposedly eyewitness drawings of sea monsters, 30-foot eels and fish the size of islands. Darwin claimed the ocean was boring, while others believed it to be frozen solid at the bottom and pitch black. Early exploration of the Deep had its own problems, too. The first submersible designs included a covered rowboat with way too many oars. Eventually, though, the blueprints graduated to include more sophisticated and streamlined changes (though even now, as we all unfortunately know, improperly designed vessels can implode, as well as get tangled in miles of fishing lines).


Casey’s cast of characters are as quirky as the ocean itself. There’s the 1930s’ William Beebee and Otis Barton who dove to 3,028 feet to discover “a pulsing nightclub of life,” but who were so resentful of each other that they never spoke again after their last dive. There was Edward Forbes who loved dredging the deep so much, he wrote a famous song about it — “The Dredging Song,” a singable ditty you can find on Google. Even James Cameron has a cameo.

Given that, as Casey notes, “virtually everything ever made by humans, from exquisite pieces of jewelry to massive building blocks for Egyptian pyramids, has been carried at one time or another by water craft,” the seafloor is littered with artifacts — a kind of spectacular underwater museum. In 2015, explorers even found the shipwreck of the San Jose galleon, which had been lost for 307 years — an astounding discovery that attracted explorers, countries, and looters, all fighting over who owned what and why, and how to salvage it.

Casey’s descriptions of the shimmeringly strange life teeming below the waves capture her wonder and ravishment in prose that morphs into poetry: squids like black kites, a creature with a Mickey Mouse head, and various inhabitants that flash off and on like neon lights, beings to rival any space alien we could imagine. “Nothing would be too unbelievable,” she writes. “There are creatures that breathe iron and creatures with glass skeletons and creatures that communicate through their skin. … Some have see-through heads. Even the most ethereal among them can handle pressures that would crush a Mack truck.”


Her depictions of diving are also enthralling. In the Neptune submersible, en route to the twilight zone, she swoons at the pale gold sandy floor and orange-splashed rocks: ”It was as though I was meeting the world for the first time.” Later, in Hawaii, she goes even deeper into the abyss, seeing the underwater volcanoes and a landscape of such dreamy unearthly beauty that “I felt as though I were melting into it, surrendering — as though I had made it home, and now I could finally rest.”

Amid the wonders, Casey turns serious with warnings. Why aren’t we protecting our oceans better instead of polluting them with synthetic fibers, microplastics, and industrial and chemical wastes? Live ammunition is routinely dumped into the sea, as well as a heavy carpet of beer cans. Our carelessness has made our oceans more acidic, exacerbating our climate problems. Now strip mining companies want to target the gorgeous deep-sea nodules that grow on the abyss’ seabed, which could destroy the microbes that live on, in, and under them, which already have been used to generate powerful antiviral and anticancer drugs.


Government funding for deep-sea science is a fraction of what it should be, and most money comes from private funding. But there is hope. Casey touts state-of-the-art, water-loving organizations like OceanX, which means to inspire change by bringing the ocean’s wonders up to dry land with cutting-edge cinematography, vivid storytelling, and science — to grip us with the same awe, excitement, and call to action as Casey’s luminous book does.

THE UNDERWORLD: Journeys to the Depths of the Ocean

By Susan Casey

Doubleday, 352 pp., $32

Caroline Leavitt’s latest novel, “Days of Wonder,” will be published by Algonquin/Hachette in April 2024.