What the Ocean Holds

Near the close of her superb recent book, The Blue Machine: How the Ocean Works, Helen Czerski writes, “I wish so much that I could have written an ocean book that ended with pure celebration…with nothing but a positive, exciting ocean future to look forward to.” That plaintive sentence introduces a chapter filled with alarming news. Here’s an overview.

Because of climate change, ocean temperatures are rising with shocking speed.¹ Billions of pounds of plastics and microplastics and nanoplastics—smaller than the dust particles we breathe—are washing into the ocean every year, affecting nearly every aquatic species in ways scientists are only beginning to understand. The excess carbon dioxide we so abundantly vent into the atmosphere is absorbed by seawater, lowering its pH and impeding the growth and survival of corals and shellfish.² Oxygen levels are declining; hypoxic or dead zones—oxygen-deprived patches of water—may now cover over 12 million square miles, roughly as much surface area as the Arctic and Southern Oceans combined.

Some of the deepest ocean trenches—called hadal trenches (after Hades)—have been found to contain what one writer calls “every toxin we’ve ever unleashed,” including PCBs and DDT. World-defining currents, like the Atlantic Meridional Overturning Current, which carries warm water north from the tropics, may be on the verge of shifting into new and potentially catastrophic patterns, due to the rush of meltwater pouring from Greenland’s glaciers and Arctic ice. And then there’s the appalling decline of fish populations caused by government-subsidized and illegal overfishing, which has severely affected the entire chain of aquatic organisms, from whales to zooplankton, and all the nutrient cycles that structure the biological ocean. According to a recent study, only 13.2 percent of the surface area of the ocean “is still wild, with zero to little impact” from humans.

Czerski’s purpose in The Blue Machine is to show us not only how the ocean works but also why it works and why that matters. She’s a physicist, and she’s interested in a physicist’s ocean: a complex overlapping and interweaving of structures, systems, forces, internal waves, and feedback loops, many of them defined by tiny variations in the salinity, temperature, or density of seawater. The ocean may look relatively uniform to us—“water, water, everywhere”—but it’s full of differentiation, full of watery “places”: masses and layers of saltwater defined not by underwater topography but by attributes of the water itself, including the pace at which it moves, or doesn’t move, around the planet. Czerski is fascinated by the ocean’s stability and its dynamism, by its energy and biology, its metabolic subtlety and wholeness.³ And what emerges from her pages is a sense of the ocean’s character: the delicate balance of powerful forces that defines it as a planet-wide physical system—an “engine,” she calls it—and a realm of intricately interlinked habitats.

In general, Czerski is describing an ocean from the not-so-recent past and one relatively unaffected by humans. Only in her final chapter does she show us the ocean as it is now—and that’s when plaintiveness rushes in. It’s one thing, she writes, to know that we’ve “built a culture based on ignoring the realities of living on a finite planet.” It’s something else again to understand and feel what that means in oceanic terms and to acknowledge the shame and anger it gives rise to. Even now, it’s tempting to think of the ocean as humans have always thought of it: a nearly infinite and incorruptible blank. Or, as Czerski might say, as humans have always not thought of it. For most of us, she writes, “this vast and crucial engine manages to be almost invisible.” Almost invisible—and almost unthinkable.

For the last three years my wife and I have spent part of the winter on the Kona coast of Hawaii’s Big Island. Our perch there is a long, open veranda some three hundred feet upslope from shore. Below lies Kealakekua Bay and the Pacific, the vestige of an unimaginable past. Four billion years ago the young, hot Earth began to cool, and as it did, its opaque shroud of water vapor condensed and fell as rain, precipitating the seas into existence. The ancient ocean before me looks like liquid time, making it all the more wonderful whenever a humpback whale appears, blowing and breaching, attesting to its existence and to mine.

Before dawn some mornings the water looks like late-winter lake ice about to melt away in a warming season. By noon the sun’s rays plunge into the shallows, brightening them into endless variations of neritic turquoise and blue and azure. At sunset the ocean is again a single coruscating surface. Beneath that bright sheen of visibility lies the invisibility Czerski is talking about—a metaphor for cultural inattention, yes, but also actual invisibility, something the ocean stores in unimaginable quantities.

In Moby-Dick, Melville calls the ocean the “dark side of this earth,” and he’s right. “Water is basically opaque to almost all light,” Czerski explains, because light entering the ocean is quickly transformed into heat. Ninety percent of the ocean’s volume lies in the aphotic (“no light”) zone, a region of near-total darkness that begins at a depth of two hundred meters and reaches to the bottom of the deepest deep, where darkness is absolute. As Czerski puts it, “almost all of the ocean is dark almost all of the time.” It’s easy to picture the visual limits imposed by the physics of light in water. Two hundred meters—a depth at which less than 1 percent of surface light survives—is a little more than two football fields, a distance we can usually see with no trouble at all. The deepest spot in the ocean—the Challenger Deep within the Mariana Trench—is 35,876 feet below the surface. Passenger planes fly that high routinely, and from a window seat on a cloudless day you can easily see the land below.

In Melville’s phrase, the Earth sounds a little like the moon, as if it were neatly divided into oceanic dark on one side and terrestrial light on the other. But Earth isn’t arranged that way. Trying to grasp the size of the ocean—its volume and extent and scale in relation to the continents—resembles the cognitive difficulty we have imagining the age of our planet or the distance to the nearest galaxy. It’s sometimes pointed out, not entirely helpfully, that all the land on Earth (by surface area) would easily fit in the Pacific Ocean. Czerski notes, too, that the abyssal plain—the broad sedimentary floor of the deep ocean—“covers more than half of the Earth’s whole surface.” I imagine land and water forming a binary system, as if they were two planets of different sizes orbiting the center of their combined mass. The small planet is the land we live on; the large planet—nearly two and a half times bigger—is ocean. The flaw in that analogy, of course, is supposing that ocean and land could ever be separate.

What life on land is, the ocean has made possible. And so, in the very long view of evolution, we humans are vestigial sea creatures. As living organisms, though, we’re incredibly alien to the “dim saltwater”⁴ covering most of the planet. One way to register the complexity of that fact is by scuba diving. Early on a bright January morning, I step off the stern of a Kona dive boat and bob at the surface near my diving partner. (We wear inflatable vests called BCDs, short for “buoyancy control device.”) At a signal, I deflate my vest and empty my lungs and—properly weighted—drift down the water column. The ocean opens below and around and above us, and soon we stabilize at depth. We establish neutral buoyancy, neither rising nor sinking, put ourselves in horizontal trim (think Superman in flight without the extended arms), and off we slowly go, into the unfamiliar.

The depth limit of recreational diving is 130 feet. That deep, you feel not so much squeezed as comprehensively embraced by the ocean. Your body—so liquid—is in equipoise with the water around it. Even at shallower depths, your sphere of visibility has a radius of at best 150 feet, but often far, far less. Color has been skewed to the blue. There may be a surge or a current. Near the mirrorlike surface, ribbons of aqueous light flicker and fade, and directly above you, the bright round patch of light called Snell’s Window seems to glisten with safety. But the surface is no longer inherently safe. The moment you started to descend, your blood began absorbing nitrogen, which your body needs to release gradually as you rise again or it will bubble outward into your joints, causing decompression sickness, or the “bends.”

And everywhere, all around you, are organisms for whom these problems—blood gases, salt levels, breathing, buoyancy, trim, orientation, and temperature control, not to mention propulsion, reproduction, digestion, and tolerating immense and varying pressures—aren’t a consideration. Evolution has solved them in every underwater creature, though the solutions differ widely. In a pattern called DVM—or “diel vertical migration”—billions of aquatic organisms of every size rise toward the surface at night all around the globe and descend again during the day, lantern fish and krill (and many other species) traveling hundreds of feet each way, an unimaginable vertical distance for a human diver. In our organismic selves, wearing wetsuit and scuba gear, we’re limited to a very few feet of ocean in its shallowest coastal fringes—a tiny fraction of the most massive feature on this planet.

But in the ocean, life is found everywhere and at every depth.⁵ “Ocean life” sounds like it means parrot fish and coral and manta rays, sea stars and sponges and octopuses. And it does. But it also means microbes, lots and lots of microbes. “We humans,” Czerski points out, “are incapable of even seeing 61 per cent of ocean biomass.” Microbes—the invisible and the barely visible—amount to 90 percent of the biomass in the ocean. Their actual numbers are staggering. Estimates range from 3.6 nonillion (10³⁰) to 100 million times the septillion (10²⁴) stars in the sky, a population kept within limits by a no less immense number of aquatic viruses. What are the microbes doing there? Among other things, they’re making at least half, and perhaps as much as 80 percent, of the oxygen we breathe.⁶

Czerski calls the ocean a “liquid powerhouse” with “components on every scale.” Imagine, for example, a columnar view of the ocean, well offshore, far beyond the continental shelf. At the surface—where wind meets wave—bubbles form and burst, moment by moment, part of the constant gaseous exchange between ocean and atmosphere. The bubbles are carried on an ocean-wide tessellation of surface eddies—whorls of water spinning and spinning. Seen in false color from a satellite, they look like the marbled endpaper of the planet. In turn, those eddies are carried on the far larger structure of the major ocean gyres, which can take years to revolve.

As you go deeper in the water column, the temperature drops and density increases. Transitions can be abrupt—a reminder that the ocean’s discontinuous layers “generally do not mix with each other.” Differences in salinity and temperature can also create channels that, according to Laura Trethewey in The Deepest Map: The High-Stakes Race to Chart the World’s Oceans (2023), “funnel underwater sound across extraordinary distances from one end of an ocean to another.”

The deeper you go, the slower the water moves and the longer since it was last warmed by sunlight. “The biggest and slowest of the surface patterns,” Czerski writes, “operate on scales of months and years rather than the centuries of the depths.” What keeps these distinct layers of water from mixing is the fact that “there isn’t a mechanism that can stir up the whole ocean quickly enough to make it all the same.” Even the Coriolis effect—caused by the spinning of our planet—isn’t powerful enough to homogenize the ocean, a fact that becomes evident when you compare the salinity of different ocean basins.⁷

One result of the way light behaves in water is ignorance. Had scientists been able to look down from the surface and see the great ocean ridges—immense volcanic mountain chains from which the ocean floor is spreading—the theory of plate tectonics would have emerged much earlier⁸ and found much swifter acceptance. There would have been little doubt, too, about the answer to a long-standing question—can life exist in the deep ocean?

But if somehow we were able to see into the deep as easily as we see on land,⁹ it would mean that the sun’s light wasn’t being converted to heat in the upper, “mixed” layer, which Czerski calls “a lid on the ocean.” And without converting light to heat, there’s nothing to connect “the powerhouse of the sun to the ocean engine which runs on that heat energy.” As Czerski describes it, the ocean’s predominant pattern is “the overall shunting of energy from equator to poles,” a connection that became clear to scientists only in the mid-1970s. The ocean is a dynamo that turns its own motion into what we know as climate.

What scientists are learning about the global ocean is changing almost as fast as the ocean is being changed. The more they learn and the closer they’re able to look, the more obvious it becomes that attaining our extraordinary powers of scientific observation—a broad cultural and societal achievement rather than a merely technological one—has radically changed the very thing we’re trying to observe. Reaching a stage of development, as a civilization, where such sophisticated tools are available has come at an almost unbelievable environmental cost. The connection is more than ancillary. The state of the ocean makes that evident. Among the many things you find when you study it closely is the record of our disregard, our foolishness, and our greed.

Identifying and understanding the ways the ocean is at risk requires well-funded scientific research, gathered and coordinated by intergovernmental organizations and accurately reported by a free press. But as Czerski reminds us, what scientists actually do depends ideally on the values that a community, a society, chooses. “Once you’ve made a decision about your values,” Czerski argues, “then science has a contribution to make, because it gives us all our best collective understanding of how to get there.” Our long-standing, hard-won confidence in the work of scientists and researchers is being intentionally undermined, not because science falters but because values differ. This is a dilemma we all face. We live within the immediacy of our own personal worlds, where a sense of “normality” is hard to displace, even as “normality” begins to look like an illusion. It’s possible that our capacity to adjust to almost any “new normal” may turn out, ironically, to be one of our greatest liabilities as a species.

Saying the ocean is terribly big is like saying it’s totally wet. It doesn’t get you very far. So let’s talk about the deep ocean, one thousand meters and below, in the zones called bathypelagic, abyssopelagic, and hadalpelagic—the midnight zone, the abyssal zone, and the hadal zone. Together they add up to three quarters of the ocean’s depth. As Susan Casey reports in her excellent book, The Underworld: Journeys to the Depths of the Ocean, it’s now estimated that Earth’s biosphere is “95 percent deep ocean.” Think for a moment what that means: most of this planet’s biosphere, as one scientist put it, “exists in the dark.” And it exists in the cold and under immense pressure—the very conditions that made earlier investigators wonder if the deep ocean contained any living organisms. And yet, to adapt the words of a mid-nineteenth-century biologist, it turns out that life has no bathymetrical limit.

Manned or robotic underwater vehicles, called submersibles, are now providing more and more detail—little enough given the scale of what’s being explored—about the strange organisms and stranger habitats concealed in the deep. No longer is it necessary to slither, like William Beebe, into a steel sphere meant to dangle like a locket at the end of a ship’s cable. (In 1934 Beebe and his partner, Otis Barton, reached a depth of 3,028 feet in the Bathysphere, the deepest any humans had ever descended.)¹⁰

The story Casey tells in The Underworld is in essence a story about the technology of deep ocean discovery—about the humans and the engineering that have made it possible to scout the ocean trenches in a vessel like the Limiting Factor, a two-seat submersible built by Triton Submarines for the independent explorer and investor Victor Vescovo. His Five Deeps expeditions in 2018 and 2019 took the Limiting Factor to the bottom of the five deepest ocean trenches on Earth. It gathered enormous amounts of scientific data. And, as on any voyage into the vast ocean recesses, the observers aboard the Limiting Factor gathered existential data too. The point of going so far down into the deep—into blackness and cold and crushing pressure—isn’t just to witness and discover new species. It’s also to feel what it’s like to go so deep, to fall so far from anything remotely familiar or hospitable.

Beebe put it this way: once the upper world vanishes, there’s “a plunging into new strangenesses, unpredictable sights continually opening up, until our vocabularies are pauperized, and our minds drugged.” Casey dove near Hawaii with Vescovo in the Limiting Factor to a depth of three miles, and she says something similar. “Above the surface,” she writes, “life can feel like it’s spinning apart, fracturing into pixels, dispersing like dust by the day. But here was solidity and eternity, and a reality bigger than anything we could imagine.” For her, the experience of diving into the abyss was epiphanic and curiously solipsistic. What looks like a form of sensory deprivation—sitting in a cramped, cold vessel, watching the water go from darkest indigo to Stygian blackness as the hours pass—turned out, for Casey, to be a form of sensory intensification. “In the deep,” she writes, “you lose your bearings and you find yourself.”¹¹

Most of us, of course, will never experience that kind of abyssal, personal repristination. What we have instead of submersibles is imagination, which is more important than it might seem. Until it’s an actual “place”—a habitat accurately visualized in the human mind—the deep ocean is a realm we can’t even begin to protect. Both Casey and Czerski value what the latter calls “the emotional relationship that we could have with the deep sea,” a phrase that sounds strange at first. After all, what kind of relationship could we have with a realm so hostile to humans, a realm in which our existence has never mattered?

A possible answer is suggested by the difficult word “wilderness,” which has come to mean, more or less, nature that remains set apart from human use in order to protect its species and habitats, whether they’re mostly well known, as on land, or almost entirely undiscovered, as in the abyss. But “wilderness” also defines its opposite—what it’s set apart from—a perception Casey makes use of in The Underworld. Writing about the twilight zone—a biologically rich region between two hundred and a thousand meters down—she says, “Show the machine world a magnificent wilderness brimming with glittering fish, and it responds in language like this,” and there follows an opaquely managerial sentence about the “sustainable capacity adaptations” needed to harvest “mesopelagic resources.” In other words, show them a wilderness, and they’ll plan extraction. Casey calls the thought of fishing the twilight zone “off-the-charts stupid,” which, unfortunately, “doesn’t mean we won’t do it.”

It’s impossible, here, to describe the complexity and strangeness of the deep ocean—a “wilderness” we’re tempted to think of as inviolable, given its inaccessibility. Its creatures, its terrains, its life processes, its geological dynamism—all these, like submersible exploration, are recent discoveries, and they provide a wholly revised conception of our planet. The deep ocean has transformed our understanding of how life originated and revolutionized our ideas about the conditions in which life itself is possible.¹² And as the seafloor begins to be mapped in more detail—a quarter of it so far—it’s worth remembering that the word “inviolable,” like the word “infinite,” when applied to earthly resources is always terribly wrong.

There is now a frenzied rush to begin deep-sea mining—“harvesting” so-called polymetal or manganese nodules scattered across sectors of the abyssal plain. The nodules range in size from marbles to softballs, and they’ve accreted over millions of years, a few atoms at a time, forming the heart of a delicate and thoroughly unknown ecosystem. How will they be mined? By dredging—a technique that industrial fishermen have used to scrape into barrenness the tops of seamounts around the globe, some of the richest habitats in the ocean. One deep-sea mining booster has said, preposterously, that each nodule is “an electric vehicle battery in a rock,” a statement that at least has the virtue of making the trade-offs clear.

Do we protect a newly discovered and wholly unstudied ecosystem?¹³ Or do we—as we’ve nearly always done before—cash it in for our benefit without concern for the harm we’re causing? The plan isn’t merely to gather these nodules. It’s also to mine the ocean’s hydrothermal vents—where wholly new forms of life and life-chemistry have been found—by grinding them down in an underwater version of mountaintop removal. Some companies have “pledged not to use deep-sea metals in their supply chains.” But in essence, the international deep-sea mining industry has been authorized to monitor itself, which makes it almost certain that the mining law of the sea will turn out to be very little law and almost no protection at all.

The only rational response to this appalling idea? Casey quotes the famous oceanographer Sylvia Earle: “Just stop. Just wait.” In those few words, Earle captures the extent and abruptness of oceanic degradation. Casey asks her if she has a favorite dive site. Earle’s answer? “Anywhere, fifty years ago.”

In her 1961 preface to The Sea Around Us (1951), Rachel Carson addresses the practice of dumping radioactive waste in the ocean. “The disposal,” she writes judiciously, “has proceeded far more rapidly than our knowledge justifies.” In that one sentence, Carson gives us a motto for the human enterprise ever since the industrial age began.¹⁴ For “disposal,” try substituting any environmentally harmful practice you can think of: burning fossil fuels, the profligate use of glyphosate and neonicotinoid pesticides, the proliferation of plastics, ubiquitous overuse of antibiotics in factory farms, unrestrained deforestation, aquifer depletion, universal beef, or deep-sea mining. Every one of these—and many, many more—has “proceeded far more rapidly than our knowledge justifies.”

It seems at times as though our knowledge has been devoted mainly to expanding and accelerating the damage we so casually do to this Earth, with only our own human needs to justify it. I find myself picturing an official UN seal of sorts: our planet skewered like a new potato on a fork and, arching above it, a gilded, prideful mission statement: To Proceed Far More Rapidly Than Our Knowledge Justifies. This is what we humans do. This is who we are, so far.