The Brilliant Abyss

Exploring the Majestic Hidden Life of the Deep Ocean, and the Looming Threat That Imperils It

Helen Scales

• Publisher: Atlantic Monthly Press
• Year: 2021
• ISBN:
  9780802158246
• Topic: Ciencias biológicas
• Subtopic: Ecosistemas y Hábitats

A journey into the alien depths of the sea, and into our possible future, from a marine biologist known for "nature writing at its most engaging" ( Sunday Express ). A golden era of deep-sea discovery is underway as revolutionary studies rewrite the very notion of life on Earth and the rules of what is possible. In the process, the abyss is being revealed as perhaps the most amazing part of our planet, its topography even more varied and extreme than its landmass counterpart. Teeming with unsuspected life, an extraordinary, interconnected ecosystem deep below the waves has a huge effect on our daily lives, influencing climate and weather systems, with the potential for much more—good or bad, depending on how it is exploited. Currently, the fantastic creatures that live in the deep—many of them incandescent in a world without light—and its formations capture and trap vast quantities of carbon that would otherwise poison our atmosphere, and novel bacteria as yet undiscovered hold the promise of potent new medicines. Yet the deep also holds huge mineral riches lusted after by nations and corporations; mining them could ultimately devastate the planet, compounded by the deepening impacts of ubiquitous pollutants and rampant overfishing. Eloquently and passionately, the author of Spirals in Time and Eye of the Shoal brings to life the majesty and mystery of an alien realm that nonetheless sustains us, while urgently making clear the price we could pay if it is further disrupted. The Brilliant Abyss is at once a revelation and a clarion call to preserve this vast unseen world.

PART ONE

EXPLORE

Here Is the Deep

Watch Earth from afar as it spins through space, and it shows itself to be a water planet. Seven-tenths of the surface is covered in what we see as blue ocean. Blue light from the sun seeps down through the seawater, leaving all the other colors behind in the shallows, where they’re absorbed by vibrating molecules of H₂o. The tenacity of those shorter wavelengths of light, 450 nanometers and under, gives Earth its particular shade of blue. But even those deepest-diving photons can go only so far. Below the first 660 feet—roughly the long side of a Chicago city block—weak remnants of dim blue sunlight remain. Below that depth, physical conditions shift and oceanic life becomes distinct from the shallower, surface seas. This is where the deep sea officially begins.

On average, the oceans are around 12,500 feet deep, or close to two and a half miles, ten times the height of the Empire State Building in New York. Below 3,300 feet there are no sunbeams at all, which means that a huge portion of the planet is untouched by sunlight. Far more permanent night fills up our world than day, but most of us don’t see those dark parts or what lies within them.

Often it’s said that more is known about the surface of the moon than the bottom of the sea, and there is truth in this. The whole of the moon has been mapped to a resolution of twenty-three feet. Meanwhile, the best map of the entire deep seabed shows only features larger than three miles across. But the astronomical comparison rather misses the point, partly because of the gaping size difference between the lunar and abyssal maps. If the moon’s surface could be peeled off and laid out on the deep seabed, it would fit almost ten times over. And even though it lies a lot farther away than the deep seabed, the moon is also a great deal easier to map than the deep, because it’s bone-dry, with no oceans or lakes in the way. With a telescope and a clear night, any of us can get a reasonable idea of what the near side of the moon looks like (accessing the dark side is rather more involved). Try doing the same for the deep seabed.

Were our view not blocked by its cloak of water—blue above, black below—Earth would look very different. We would see the complex topography of the deep ocean floor laid out in a spectacular terrain.

Most obviously, our planet would look like it had exploded and been crudely stitched back together again. Great jagged scars across the deep seabed mark the world’s longest, most dramatic mountain range. Composed of geological formations known as mid-ocean ridges, the mountain range threads for 34,000 miles, its underwater peaks up to 2 miles high and in places almost 1,000 miles wide. Portions of this mountain range are named mostly for their geographical locations: the Mid-Atlantic Ridge bisects the Atlantic from Greenland all the way south toward Antarctica; slicing across the Indian Ocean are the Southwest, Central, and Southeast Indian Ridges; skirting south of Australia and New Zealand, the mountain range continues as the Pacific-Antarctic Ridge, then veers north as the East Pacific Rise toward California. Other segments connect to the great mountain chain: the Aden Ridge is located between Somalia and the Arabian Peninsula; the Chile Rise stretches through the eastern Pacific toward the tip of South America; the 300-mile-long Juan de Fuca Ridge passes offshore from the Pacific coast of North America between Oregon and Vancouver Island. All these peaks form at the edges of seven major and numerous minor tectonic plates, the giant jigsaw puzzle pieces of the earth’s outermost rigid layer, the crust, which glide around on the viscous mantle beneath them. Wherever submerged tectonic plates pull apart, lava erupts from deep within the mantle, pushing up the mid-ocean mountain peaks and oozing brand-new seafloor that spreads sideways, forming a basaltic, oceanic crust between three and six miles thick.

Frequently, the mountain range doesn’t stretch in smooth lines across the seabed but is broken and offset in giant corrugations. Fracture zones form when sections of rifting tectonic plates slip past each other, triggering earthquakes and sending tsunamis racing across the oceans.

Moving away in various directions, the abyssal plains begin to either side of the soaring peaks of mid-ocean ridges—to the east and west of the Mid-Atlantic Ridge, north and south of the Pacific-Antarctic Ridge. Lying between 10,000 and 16,400 feet below the sea surface, these prairies of the deep go on and on. With their horizontal spread, they collectively form the biggest feature of the seabed and cover more than half of the earth’s surface; even the vast Eurasian Steppe, the belt of grasslands ranging between Hungary and China, is dwarfed by the abyssal plains. These swaths of the abyss are soft underfoot, should you decide to go for a walk there; in most places you would have to dig through a mile of mud before hitting rock on the seafloor beneath, and in some places more like six miles. A map of the globe’s seafloor sediments, newly updated in 2019, suggests there is 30 percent more mud than previous studies had estimated. The sediments are a mix of flecks of eroded rock washed out in rivers, dropped by glaciers, or blown in the wind, together with the minute bodies of planktonic creatures that sprinkle down from the surface and settle in great seabed slicks.

Abyssal plains are not simply endless, flat tracts of mud. They are intersected by undulating hills and winding valleys, burping mud volcanoes and fizzing Jacuzzis of methane bubbles; and dotted across the plains stand thousands of tall volcanoes, active or inactive, cone-shaped or flat-topped if they were worn away by waves in past times when they reached the sea surface. Known as seamounts, these isolated peaks are distinct from the ranges of mid-ocean ridges, although they can form nearby. The biggest mounts are generally located in the central regions of tectonic plates, in places where chambers of molten magma bubble up in hot spots through the oceanic crust. As tectonic plates slide over these hot spots, chains of seamounts form one after another, like cakes being made on a factory conveyor belt.

Journey across an abyssal plain, skirting the seamounts and facing away from a mid-ocean ridge, and you will pass over gradually older and older seabed until eventually you reach the brink of the very deepest parts of the ocean. Tectonic plates collide at subduction zones, where one plate gets thrust under another. Here, as old sea-floor is dragged down into the earth’s molten interior, to be melted and recycled, oceanic trenches are formed, reaching to depths of 20,000 feet and more. Principally formed from twenty-seven trenches worldwide, this is the hadal zone, named after Hades, the ancient Greek god of the underworld.

In cross section, trenches are V-shaped and can stretch horizontally for thousands of miles. The Atlantic and Indian Oceans each contain a single trench, the Puerto Rico Trench, north of Puerto Rico and the Virgin Islands,^* and the Java Trench, skirting south of the Indonesian islands of Java and Sumatra, respectively. In the Southern Ocean beyond the tip of Tierra del Fuego lie the South Sandwich and the South Orkney Trenches. The remaining trenches are all located around the Ring of Fire, a horseshoe-shaped region fringing the east, north, and west of the Pacific, where multiple tectonic plates meet, causing intense seismic activity and 90 percent of the world’s earthquakes. A string of trenches running from Russia to New Zealand are all more than 32,000 feet deep: the Kurile-Kamchatka, Philippine, Tonga, and Kermadec Trenches, plus the deepest of all, the Mariana Trench, which spikes below 36,000 feet.

Seismologists make sure to listen very carefully to trenches. Located at subduction zones, where tectonic plates push and shove each other, the steep trench walls regularly heave and shake with the world’s most powerful earthquakes. An array of sensors strung through the Japan Trench is poised to detect rumbles that could foretell the next mega-earthquake, like the one that caused the devastating 2011 tsunami, which killed eighteen thousand people and flooded the Fukushima Daiichi power station, causing the worst nuclear accident since Chernobyl. In April 2020, a panel of advisers to the Japanese government warned that a massive earthquake and tsunami could strike the northern region, around Hokkaido, at any time. While they can’t say exactly when it will happen, the advisers studied ancient sediments and discovered that a huge quake has hit every three hundred to four hundred years—and the last time was in the seventeenth century.

Retreating from the shuddering hadal zone, back across the calm and quiet abyssal plains and toward land, the deep seafloor comes to an end where the continental shelves begin. To get up onto the shallow plateaus, those familiar parts of the ocean that reach the coast, great piles of sediments must be clambered over, an area called the continental rise. Then come the escarpments of the continental slopes like giant cliff faces, which are sliced through with nine thousand or so steep-walled canyons. Many great rivers, including the Amazon, Congo, Hudson, and Ganges, lead toward underwater canyons formed not by persistent water flow, as river channels are, but sculpted by underwater landslides as sediments build up and slump off the edges of the continental shelves. On average, submarine canyons are twenty-five miles long and a mile and a half deep, and many are even more dramatic. Nazaré Canyon is Europe’s largest, running 130 miles toward the Portuguese coast, where it funnels the wild Atlantic swell into record-breaking waves. It was here, in 2017, that Brazilian big-wave rider Rodrigo Koxa surfed the biggest wave anyone ever had (80 feet), and in 2020 his compatriot, Maya Gabeira, set the women’s record (73.5 feet), which was also the biggest wave surfed by anyone during that winter season, a first for women in professional surfing. On the other side of the planet, in the Bering Sea off Alaska, Zhemchug Canyon is sixty miles wide, compared to the Grand Canyon’s eight miles. And America’s iconic terrestrial canyon is half the height of the oceans’ most impressive equivalent, the Great Bahama Canyon, whose walls tower 14,060 feet (almost three miles) up from the abyss.

But this grand panorama of the ocean floor is hidden away beneath so much seawater. The total volume of the deep ocean water, everything below 660 feet, is roughly 240 million cubic miles. To put this in perspective, the Amazon River pours out a single cubic mile’s worth of water every five and a half hours. At that rate, it would take approximately 150,000 years to fill up the entire deep.

That isn’t how the ocean basins originally came to be full of water, however. For almost as long as Earth has existed, there have been oceans, although how so much water ended up here has been an enduring mystery among cosmologists. Many consider it likely that water was imported from the outer reaches of the solar system when icy comets bombarded the early Earth. Traces of water detected in dust particles from a peanut-shaped stony asteroid called Itokawa indicated that half of Earth’s water supply may have come from this common form of space rock. Earth may also have come preloaded with some of its own primordial water, lodged deep within rocks that coalesced and formed the planet 4.55 billion years ago. Conditions were much hotter back then, and minerals rich in hydrogen and oxygen would have melted and reacted together, and spewed the resulting water from the planet’s crust; the water would then have evaporated and risen into the newly forming atmosphere. Subsequently, as Earth cooled, the water vapor condensed, clouds formed, and it started to rain—perhaps as early as 4.4 billion years ago—beginning to form the oceans.

The ancient history of the oceans is difficult to tell because their geological record is continually wiped clean.^* Oceanic crust is thin, young, and short-lived compared to the thick, primeval continents floating above the rest; seafloor exists for tens or maybe hundreds of millions of years (not long, in geological terms), before getting dragged back into the earth at subduction zones, to be melted, recycled, and squeezed back out as new oceanic crust. Occasionally, a slab of ancient seafloor has been pushed up onto a continent, where it remains for geologists to inspect and reconstruct what happened long ago. One such chunk of primordial seabed found in the Outback of Western Australia has offered a glimpse into the past, hinting that more than three billion years ago, most of the planet was covered in water. Chemical traces in these rocks point toward the existence of a water world, devoid of enormous, soil-rich continents but with microcontinents peeping up above the waves here and there, little more that rocky islets. In time, the full-size continents emerged, and as the eons passed, they began to perform a slow, shuffling dance around the planet, and around them the shape of the global ocean has continually changed.

Partially enclosed basins have formed, and ancient oceans have come and gone. Superoceans formed at times when the continents were all clustered together, surrounding them with water. A billion years ago, a vast ocean called Mirovia is thought to have encircled the supercontinent Rodinia. The continents split apart, then came together again, most recently 355 million years ago, forming Pangaea, encircled by the superocean Panthalassa, which eventually fragmented into the oceans we know today. The oldest, biggest, and deepest is the Pacific, which is at least 250 million years old; next the Atlantic, Indian, and Arctic Oceans formed; and finally, 30 million years ago, the Antarctic and South American continents pulled apart, and the Southern Ocean began its clockwise swirl around the bottom of the planet.

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The expanses of the deep seabed, the abyssal plains and seamounts, canyons and trenches, plus all the water above them, constitute the single biggest living space on the planet. More than 95 percent of the earth’s biosphere—the volume of habitats available for living organisms to occupy—is made up of the deep sea. Everything else—the forests and grasslands, rivers and lakes, mountains, deserts, and shallow coastal waters—is collectively outstripped in terms of sheer volume by those colossal reaches of the oceans that lie below the blue surface.

If you were to sail out into the open ocean and drop a glass marble over the side of the boat, for the first six or seven minutes it would fall through the uppermost layer of water, the part where the sun still shines. Some call this the epipelagic or euphotic zone, or simply the sunlit zone. It’s the most familiar part of the oceans, where most of the known species live, and it’s where all the oceans’ photosynthesis takes place. The sun-catchers come in the form of large seaweeds as well as microscopic, single-celled creatures, collectively known as phytoplankton,^* which all suck in carbon dioxide and turn it into food for almost all the rest of ocean life.

As the marble drops, the sunlight fades unt...