In June 1931 subscribers to The National Geographic Magazine read of an astonishing journey. William Beebe of the New York Zoological Society and his companion Otis Barton had descended a quarter of a mile into the ocean—to “Davy Jones’s Locker” as the article announced—and lived to tell the tale. A revolutionary vehicle, a “bathysphere,” designed and built by the pair following a sketch by Theodore Roosevelt, had made the voyage possible. Although not taken seriously by most scientists at the time, the descent began an era of exploration that would ultimately reveal to us a hidden nine tenths of our world.

The historic expedition took place eight miles off New Nonsuch Island, Bermuda, on June 11, 1930. Crammed into a steel ball weighing two tons, with only a round six-inch window to peer out of, Beebe and Barton (who was too busy managing the bathysphere to look out) found themselves suspended in a blue-black world that was then as unknown as the dark side of the moon. Beebe, who transmitted his thoughts and observations to a barge on the surface via telephone, related:

Since…the Phoenicians dared to sail the open sea, thousands upon thousands of human beings had reached the depths at which we were now suspended, and had passed on to lower levels. But all of these were dead, drowned victims of war, tempest, or other Acts of God.*

What Beebe saw on that trip—and reported with such vividness—was a glowing world of creatures so astonishing that for decades many doubted his veracity. The clear sea stretched endlessly, and was so full of luminescence that it sparkled like the night sky. Cavalcades of black shrimps, transparent eels, and bizarre fish approached the descending sphere, and when Beebe used his spotlight to see them, great shadows and shifting patches of light hovered just out of view, leading him to postulate the existence of giants in the Bermudan depths. And below the bathysphere? There, said Beebe, lay a world that “looked like the black pit-mouth of hell itself.”

Is it the geography of Christian belief that has made us upright apes so dread the ocean deep, yet strive so mightily to explore the cold and (so far as we know) lifeless heavens? Not all human beings think as Beebe did. The Greenland Inuit, for example, believe that paradise lies at the bottom of the sea, for that is where their food comes from. It is the cloudy, frozen mountains and sky that they fear and shun. Whatever the cause, human beings know more about the surface of that dead rock we call the moon than the living depths of our own planet’s seas. We still know very little about the deep ocean floor.

Just what we have missed out on as we have pursued our heavenly dreams is revealed in two new books—Claire Nouvian’s The Deep and Tony Koslow’s The Silent Deep. So much of the knowledge they contain is new that until very recently it would not have been possible to write such books. From the time of Pliny until the late nineteenth century, Koslow informs us, humans believed that there was no life in the deep. It took a historic expedition in the ship Challenger between 1872 and 1876 to prove Pliny wrong; its deep-sea dredges and trawls brought up living things from all depths that could be reached. Yet even in the twentieth century scientists continued to imagine that life at great depth was insubstantial, or somehow inconsequential. The eternal dark, the almost inconceivable pressure, and the extreme cold that exist below one thousand meters were, they thought, so forbidding as to have all but extinguished life. The reverse is in fact true: the most common backboned creature on our planet is a fish known as the benttooth bristlemouth, and it is only found in the deep sea. Yet who has ever heard of it?

Only the uppermost part of the oceans—the top two hundred meters—bears any resemblance to the sunlit waters we are familiar with, yet below that zone lies the largest habitat on Earth. Ninety percent of all the ocean’s water lies below two hundred meters, and its volume is eleven times greater than that of all of the land above the sea. This great realm is divided into a twilight zone—between two hundred and one thousand meters deep—and a zone of total darkness, which is itself varyingly subdivided. Below six thousand meters lies a region known as the hadal zone (a term coined only in 1959 from the French Hadès); in the Marianas Trench off the Philippines it is 11,000 meters deep. Ships plying the waters over the trench glide as far above Earth’s surface as do jet aircraft crossing the face of America.

The hadal zone with its freezing water, heavy pressure, and darkness is seemingly harsh, but some of the imagined hardships are illusory. The freezing water, for example—which comes from the Antarctic seas—carries oxygen necessary for life. Were it much warmer the oxygen content would be insufficient to support fish and giant squid. And while the pressure is extreme (at just four thousand meters deep it is equivalent to that of a cow standing on your thumbnail) the creatures of the hadal zone don’t feel it, because the pressure inside their bodies matches that without. And while there is no sunlight, light from luminescent creatures abounds.


A small intimation of the wonders to be seen in this new-found world is given at the beginning of The Deep. There, a full-page spread is devoted to a photograph showing the submersible vehicle Alvin floating before the sixty-meter-tall hydrothermal chimneys in the Atlantic Ocean known as “the Lost City.” The vehicle’s lights illuminate a stupendous scene through water so clear that the photo looks as if it were taken in air. The image seems to embody the awe and wonder of the deep, as well as the extent of our ignorance about this remarkable place.

Our species has made just one visit to the deepest point of the oceans. The Marianas Trench is the sump of the earth: at eleven kilometers deep it could swallow Mount Everest and still have two kilometers to spare. On January 23, 1960, Swiss scientist and engineer Jacques Piccard and US Navy lieutenant Don Walsh boarded their vessel Trieste (a direct intellectual descendant of the bathysphere, though incomparably more sophisticated and capable) and began their five-hour dive. As Trieste nudged the silt at a depth of 10,910 meters, Piccard glimpsed a flat, fish-like creature moving away. To this day, that fleeting observation is all we know of higher life at the bottom of the hadal zone.

Since Trieste’s historic descent, a robot called Kaiko has explored more of the hadal zone, discovering a fragile, floating world of jelly life, insubstantial organisms that are able to exist only because the water is so still that currents don’t tear them apart. On the very bottom Kaiko has glimpsed sea cucumbers, worms, and giant single-celled organisms up to twenty-five centimeters across, which feed on the slow rain of organic matter that sinks from the sunlit zone eleven kilometers overhead. Because deep trenches are often close to land, wood washed out to sea by typhoons and other severe storms contributes to this supply of falling food, so that at the very bottom of our world live worms and crustaceans that dine upon hearts of palms and other rainforest delicacies.

Lately, news of such wonders from the abyss ceased coming to us, for Kaiko was lost at sea in 2003 and has not been replaced. Despite the fact that less than 1 percent of the ocean deep has been mapped, today our explorations are restricted to depths of six thousand meters or less. We will doubtless discover much of great interest in these less-than-hadal depths, yet I wonder at the wisdom of setting our hearts on a return to the moon, and perhaps voyaging to Mars, rather than further exploring the deep.

Claire Nouvian’s wondrous book The Deep contains the finest collection of photographs of the denizens of the deep that I know of, and as Dr. Marsh Youngbluth recounts in one chapter, the lives of these creatures are shaped almost entirely by “finding something to eat and someone to love.” Such needs are acute in the deep ocean, for food there is scarce and mates are few and hard to find. Yet life has adapted: fish living a kilometer or more down require only a hundredth as much energy as surface species. Their metabolism is so slowed that to us more active beings they seem to be almost suspended between life and death. Their very bodies are insubstantial—the scientists of the Challenger expedition were the first to note that they possessed a “diminished amount of earthy matter.” In fact, 85 percent of their bodies is water.

To understand the full extent of the constraints that the abyss places on life, consider the black seadevil. It’s a somber, grapefruit-sized globe of a fish—seemingly all fangs and gape—with a “fishing rod” affixed between its eyes whose luminescent bait jerks above the trap-like mouth. Clearly, food is a priority for this creature, for it can swallow a victim nearly as large as itself. But that is only half the story, for this description pertains solely to the female: the male is a minnow-like being content to feed on specks in the sea—until, that is, he encounters his sexual partner.

The first time that a male black seadevil meets his much larger mate, he bites her and never lets go. Over time, his veins and arteries grow together with hers, until he becomes a fetus-like dependent who receives from his mate’s blood all the food, oxygen, and hormones he requires to exist. The cost of this utter dependence is a loss of function in all of his organs except his testicles, but even these, it seems, are stimulated to action solely at the pleasure of the engulfing female. When she has had her way with him, the male seadevil simply vanishes, having been completely absorbed and dissipated into the flesh of his paramour, leaving her free to seek another mate. Not even Dante imagined such a fate.


It says much of our ignorance that the very largest denizens of the deep have never been captured or seen alive. It was only in April 2003 that a species known as the colossal squid was recognized as the largest of all invertebrates, exceeding even the giant squid in size. Only one juvenile and a three-quarters-grown female have been captured to date: yet the creature is not rare, making up three quarters of the diet of the sperm whale. Studies of squid beaks taken from the bellies of such whales reveal that for the great majority of squid families, the very smallest squid eaten by the whales exceeds in size the largest example ever caught by a scientist. Those enormous creatures that lurked just beyond the reach of William Beebe’s searchlight remain, it seems, even today beyond our ability to apprehend.

The Deep teaches us that nothing in the deep oceans is as it seems. Octopuses can look like cartoon elephants or red-robed clowns cheekily sticking out a tongue. Worms can look like pink floating pig butts that have somehow become detached from the rest of the pig, and squids can look like surreal cockatoos—except that they’re ten feet in length (see illustration). Suspended in crystal-clear water that extends endlessly in all directions, shape-changing is the only defense for some. When threatened, the googly-eyed glass squid (whose eyes stand out on stalks) can change shape from long and thin to spherical, so that it looks like an inedible jelly. If this fails to deter a predator, it draws in its head and releases ink into its spherical body, thus disappearing into the dark.

In a world where there is nowhere to hide, being see-through is also a good strategy—which means that many of the creatures of the deep are simply invisible to us even if they’re a meter across and at the end of our nose. The sea-jellies and like creatures specialize in this kind of defense; they are innumerable in the deep, and dominate life there.

Some jellies, however, do not take refuge in invisibility and instead are as beautiful and surreal as dreams. The red paper lantern medusa looks like an exquisite Japanese lantern, while an unnamed species looks like a vermilion flame in a cage of ice. Others appear as bolts of electric current, bells, brains trapped in gelatinous cages, or displays of fireworks. The predatory tunicate, a species of sea squirt, looks like a voracious, headless mouth on a glass stalk, and is unique among tunicates in being a true predator—its mouth closing swiftly on shrimp and other crustaceans that stray into it.

Surely the most distinctive feature of life in the depths is the frequency with which it creates its own light. This phenomenon is called bioluminescence, and anyone who has cruised a tropic sea at night will know of it. While rare on land (fireflies and glowworms are among the few land-based creatures that possess it), it is virtually ubiquitous among creatures of the oceanic midwaters. Just why so many midwater creatures possess the ability to glow and flash remains somewhat mysterious; but camouflage, signaling to a potential mate, deception of prey, and creating diversions are all carried out in the ocean by creatures using bioluminescence. Whatever its uses, this living light is the only illumination in the deep ocean world.

In what might be called the oases of the deep, life takes on a very different appearance. Among the most interesting and little known of such oases are the seamounts. These places are, as their name suggests, mountains in the sea, and because currents speed up as they pass over and around them, bringing nutrients closer to the surface, here there is a greater availability of food. Mention corals and most of us think of tropical reefs, but the seamounts are home to an astonishing variety of corals that never see the light of day. Known as black, golden, and red corals, the bony skeletons of these organisms are considered gemstones. But who, wearing such gems, is aware that they come from coral forests that can reach sixty meters in height, and support an abundance of life that rivals a tropical rainforest?

The life supported by these coral forests ranges from the exquisite to the nightmarish. Red and white crabs crawl through the coral glades, as do medusa sea-stars, their arms twining restlessly like miniature serpents. And at the very bottom of some seamounts in the Pacific Ocean can be found the blobfish. This creature, with its pale, floppy flesh, comical W.C. Fields–like nose, piggy eyes, and broad, downturned mouth complete with “cigar,” looks like a cartoon character. Its “cigar” is in fact a parasitic crustacean known as a copepod, but no one knows what the blobfish does with its comical nose.

Certain kinds of fish congregate above the seamounts to reproduce. One of the better known is the orange roughy, or deep-sea perch. When fishermen discovered these breeding congregations they found that they could scoop up a million dollars’ worth of fish in a trip, and the restaurants of the world were suddenly offering their succulent fillets. In the process, however, the fishermen destroyed the coral forests with their heavy trawling equipment. Some corals have been radiocarbon-dated to two thousand years old, suggesting that they are the Methuselahs of the sea, but their destruction was just the beginning of the tragedy. Studies revealed that orange roughy, although just a foot long, can live for a century and a half. There seems something terribly wrong about eating a 150-year-old fish, and as soon as I learned this, I stopped ordering them. Orange roughy do not even reach sexual maturity until they’re thirty, and they may breed successfully only once every few decades. Trawling them up in their thousands is like mining; the pillaged stocks will not recover in our lifetime, if ever.

An even more astonishing habitat exists in the very middle of the ocean basins, where the oceanic crust is being torn apart. Here hot rocks from the earth’s mantle come close to the surface, and hydrothermal vents can develop. Minerals come to the surface in the superheated seawater, and these are used by creatures that are entirely independent of energy from the sun. Worms two meters long, great hosts of shrimps, and foot-long clams dominate these ecosystems, all of which host bacteria in their bodies that are able to use minerals to generate energy. The extent of their dependence on their resident bacteria is such that many ocean vent species lack mouths and guts.

The dead sailors that preceded Beebe to Davy Jones’s Locker doubtless provided a temporary oasis of plenty for other specialized feeders. And they were not the first to pass this way, for from the time that mammals returned to the sea over 40 million years ago, the bodies of whales have been drifting into the hadal world, and a whole ecosystem has evolved around exploiting these unpredictable windfalls. The carcass of a whale can lie on the floor of the deep for fifty years, and over that time different kinds of creatures monopolize it. First in are the sharks and hagfishes, the black eel-like creatures with radial, rasping maws that strip the flesh. Then come worms, crabs, and bacteria, which feed until only the bones remain.

Only then do bizarre worms known as Osedax (meaning bone eaters) take the opportunity to feed. These worms have no mouth or gut. Instead they sprout a root system that penetrates the bone, and also shelters a unique kind of bacteria known as the Oceanospiralles, which specialize in breaking down complex organic compounds. It is these bacteria that feed the worms. Genetic studies reveal that Osedax worms diverged from their less specialized relatives around 42 million years ago, when the first whales evolved. Remarkably, given the erratic nature of their food supply, these worms seem unable to travel more than a few miles to locate another carcass. Because whaling has reduced the number of whales to a sixth of what it once was, the increasing rarity of whale carcasses in the deep may have already led to the extinction of some of the specialized creatures that feed on their bones.

While the hadal zone is almost entirely unexplored, it is not untouched, for humans have been bombarding it with an array of materials ranging from deadly toxins to entire ships. The number of vessels lost to the deep during wars is well known, but what is more surprising is the number lost in peacetime. According to Lloyd’s register, an average of one ship was lost at sea every two days between 1971 and 1990, and a great many go down with their cargoes and polluting fuel oil aboard. Yet these are some of the mildest threats to the abyss. Until 1972 it was a common practice to dump unwanted munitions at sea, including chemical weapons. Britain alone has dumped 137,000 tons of unwanted chemical weapons at sea, and some of the chemicals still remain in solid form on the bottom.

Following 1946 a far more ominous kind of waste began to be dumped—radioactive material. Until the practice was banned in 1993, 142,000 tons of such waste had been dumped in the North Atlantic alone. Secrecy makes it difficult to know the full extent of the problem, but in 1993 it was revealed that the Russians had illicitly dumped seventeen entire nuclear reactors into the Arctic Sea. Some marine creatures concentrate radioactive elements in their bodies. The liver-like glands of one species of shrimp, for example, have levels of polonium-210 a million times that of seawater, which makes scientists worry about the consequences of this deadly dumping.

Other pollutants include industrial waste and sewage, compounds that, among other effects, cause sex changes in mollusks, as well as chlorinated hydrocarbons (the villains of Rachel Carson’s Silent Spring), mercury (most of which comes from burning coal on land, and provides the reason why pregnant women should abstain from fish), and cadmium, which can destroy organs in humans. As Tony Koslow piquantly reminds us, “neither distance nor depth shields the deep sea from pollution.” Rather, our pollutants rain down from the sky and sea surface in a relentless stream, and like the sump of an engine, the deep is where much of the muck accumulates. But unlike a sump, the pollutants of the deep don’t stay there. Instead they find their way back to us in the fish we eat.

The Deep and The Silent Deep teach us an important lesson. The ocean depths are not some hellish and distant zone, but are an element of our living planet which is connected in very intimate and immediate ways to ourselves. They are also our last frontier, where wonders innumerable await the next generation of brave bathynauts who choose to journey there. Let us hope that we do not destroy this amazing place before they get their chance.

This Issue

December 20, 2007