What compels us to explore the ocean? ‘The Deepest Map’ by Laura Trethewey offers a deep, page-turning dive

“We know more about the surface of the moon than we do about the bottom of the ocean.” It’s a sentiment that might explain the impulse to court danger and dive into the unknown, as the tourists on the OceanGate Titan submersible did, hoping to get a glimpse of the mystery at the bottom of the ocean.

That sentiment serves as the starting point for “The Deepest Map: The High-Stakes Race to Map the World’s Oceans,” the transfixing and eye-opening new book from writer and journalist Laura Trethewey. “This sentence or one like it appears in almost every article you read about the deep sea nowadays,” Trethewey continues. “Whenever I read it, I always found myself wondering why: Why do we know so little about the ocean? And why does it make sense that we know more about the other planets than we do about our own?”

To answer these questions, Trethewey embarked on an epic journey, largely rooted around the Nippon Foundation-GEBCO Seabed 2030 Project, an initiative “to finish a complete map of the world’s sea floor by the end of the next decade,” incorporating a combination of direct exploration and crowdsourcing, using “vessels already at sea, from cruise ships to luxury yachts.”

The shape of the book, and Trethewey’s character-focused approach, results in a powerful, almost thrilling reading experience despite the complexity of its scientific material.

“The Deepest Map” bounces between two separate narratives. The first follows Cassie Bongiovanni who, upon graduating with a masters in ocean mapping, takes as her first job a shipboard mapping gig for Victor Vescovo, who used his private equity-earned fortune “to build a modern explorer’s life centred around adventure.” He had already climbed the highest mountains on every continent and skied to both poles when he decided to complete Richard Branson’s aborted Five Dives quest: “to dive to the deepest point of all five oceans.” Bongiovanni was aboard to map the sea bottom for those dives, and to ensure he was really hitting the deepest points, setting records it would be difficult to challenge.

The other narrative strand follows Trethewey herself. The author (she was named a Rising Star by the Writers’ Trust; her first book was “The Imperilled Ocean: Human Stories From a Changing Sea”) was born in Toronto and now lives in San Diego. Readers follow as she joins an expedition mapping sections of the American west coast, travels to Nunavut to explore how Inuit are adapting to the changing seas (and mapping those changes), witnesses a conference on submarine naming rights via Zoom, attends a meeting in Jamaica about the future of undersea mining, and dives in the Gulf of Mexico in search of archeological evidence of precontact societies on Florida’s sunken continental shelf. The fact that Florida has “lost roughly half its land since the last ice age” owing to rising sea levels is just one of the many — and disturbing — revelations provided by “The Deepest Map.” She also gives an overview of the history of ocean-mapping, explores in detail the difficulties involved, and introduces readers to significant figures in that world, both past and present.

“The Deepest Map” is something of a page-turner, a book which is open to the excitement of exploration, but also keenly aware of the potential dark future on the horizon. After having read of the wonders of the ocean floor, and the lengths to which explorers have gone to discover them, the chapter on the logistics and legalities of undersea mining is heartbreaking, with images of destroyed ecosystems, only newly discovered, which will haunt your dreams.

As she writes late in the book, “In the summer of 2022, the first crop of deep-sea tourists visited the Titanic, paying $250,000 for a submersible ride to the storied shipwreck lying 13,123 deep in the Atlantic Ocean. Now that the deep sea is starting to host its first tourists, miners can’t be far behind.” The Deepest Map balances the sheer joy of discovery with the seemingly inevitable consequence of that discovery: as human history has shown, that which is mapped can, and will, be exploited. Will we allow it? As Trethewey writes, “This time, map in hand, I hope we find the right path.”

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