The 64,373.76 kilometre fire under the sea
Picture a volcano. Now imagine that its main vent extends in a line. Now imagine that this line is so long that it runs for more than 40,000 miles (64,373.76 kilometres) through the dark recesses of all the world’s oceans, girding the globe like the seams of a baseball.
Welcome to one of the planet’s most obscure but important features, known rather prosaically as the midocean ridges. Though long enough to circle the moon more than six times, they receive little notice because they lie hidden in pitch darkness. Oceanographers stumbled on their volcanic nature in 1973. Ever since, costly expeditions have slowly explored the undersea world, which typically lies more than 1 mile down.
The results can make the visions of Jules Verne seem rather tame.
The ridges feature long rift valleys and, down their middles, giant fields of gushing hot springs that shed tons of minerals into icy seawater, slowly building eerie mounds and towers that can be rich in metals like gold and silver. One knobby tower in the Pacific Ocean, nicknamed Godzilla, grew 15 stories high. Thickets of snakelike tubeworms and other bizarre creatures often blanket the hot features, as do hungry prowlers such as spider crabs.
The riot of life coexists with springs hot enough to melt lead or the plastic windows of mini submarines. With extreme care, humans and robots have measured temperatures as high as 780 degrees.
To date, the studies have been episodic. Ridge expeditions venture out fitfully, their schedules determined by fickle weather and budgets, not to mention the vagaries of crew and gear availability.
Now, scientists have inaugurated a major new effort. Off the West Coast, they have wired up a highly active ridge with hundreds of sensors and cameras, as well as cables that flash the readings to shore. The ocean observatory is to operate for at least a quarter century, replacing sporadic glimpses with continuous scrutiny.
This month, the surge of data is hitting the Internet. Hundreds of scientists around the globe will now be able to monitor one of Earth’s most restless and enigmatic features as effortlessly as reading their email.
“We’re seeing it come alive,” said Maya Tolstoy, a marine geophysicist at the Lamont-Doherty Earth Observatory of Columbia University. She recently got a preview that included an eruption. “It’s exciting,” she added. “We’re just starting to understand what’s going on.”
John R. Delaney, an oceanographer at the University of Washington who conceived of the observatory decades ago, said it would help scientists better grasp not only the volcanic ridges but the surrounding waters, which cover most of the planet.
“Suddenly, a technological door has opened on studying the ocean from within,” he said. The new perspective, he added, “is the only way we’re ever going to understand its true complexity — the hundreds of processes.”
A main question is to what extent the volcanism changes over time. The old idea was that the eruptions of oozing lava and related activity occurred at fairly steady rates. Now, studies hint at the existence of outbursts large enough to influence not only the character of the global sea but the planet’s temperature.
Experts believe the activity may carry major repercussions because the oceanic ridges account for some 70 percent of the planet’s volcanic eruptions. By definition, that makes them enormous sources of heat and exotic minerals as well as such everyday gases as carbon dioxide, which all volcanoes emit.
“It’s a whole new perspective on how the Earth works,” said Daniel J. Fornari, a senior scientist at the Woods Hole Oceanographic Institution on Cape Cod, Massachusetts. “We’ve got our eyes and ears on a part of the seafloor that’s really dynamic.”
The heat below
The source of all of this activity is the slow churning of Earth’s molten interior, which continually rearranges the planet’s two dozen or so large crustal plates. The volcanic ridges mark the places where oceanic slabs slowly pull apart, giving molten rock and gases an escape route.
The first volcanic hints came to light in 1973 when mini submarines dived on the mid-Atlantic Ridge. It runs for nearly 10,000 miles, making it the planet’s longest mountain chain. The French-American team expected to see the rocky folds and fissures typical of regions on land where plates pull apart, known as divergent boundaries. Instead, they found beds of hardened lava.
The excitement rose in 1977 when an American submersible off the Galápagos Islands dived to a deep ridge. Over a hydrophone, from the seabed, a puzzled scientist told the mother ship that the volcanic site bore abundant life — contrary to the usual desertlike portrayals of the deep sea.
“There’s all these animals down here,” the expert reported. The unexpected fauna included red shrimp, brown mussels, pink fish with undulating tails, and dense stands of tubeworms with bright red plumes.
In the 1980s, scientists found that the hot vents could discharge giant plumes of warm, buoyant water. Zooplankton — clouds of tiny sea creatures — turned out to flourish in the mineral-rich plumes. The tracking of whale calls suggested that the giant mammals fed on the dense swarms.
Last year, a more basic discovery came to light. A team of 11 scientists reported that the blistering hot springs act as global recycling centers that turn complex carbon from ages of deceased oceanic life into much simpler chemicals that can form new organisms.
“They replace it with material that’s biologically reactive,” said Jeffrey A. Hawkes, a marine chemist at the University of Oldenburg in Germany, who led the research. “They’re the lifeblood of the deep sea.”
Song of fire in the depths
Starting in the 1990s, oceanographers received a glimpse of what continual monitoring had to offer when the Navy shared its long-secret network of undersea microphones, used during the Cold War to track enemy submarines. Suddenly, marine scientists could hear the volcanic eruptions and study their aftermath.
Recently, Tolstoy of Columbia University drew on such acoustic data from nine seabed eruptions over nearly two decades to paint a group portrait full of surprises. It turned out that all of those eruptions, from the Pacific, Atlantic and Arctic Oceans, took place from January to June.
The cause, she proposed, is Earth’s slightly elliptical orbit around the sun. That changes the strength of the sun’s gravitational pull on Earth during the year and, as a result, the magnitude of the tides that squeeze the planet. She said the eruptions coincided with the annual letup of the squeeze. More boldly Tolstoy suggested that such mechanisms might help explain how the planet’s regular ice ages end so abruptly — long a mystery.
Ocean levels fall sharply in such bitterly cold periods as water is tied up in massive continental ice sheets. In a paper, she proposed that the reduced pressure on the ridges might let them erupt far more frequently. As a result, more carbon dioxide would spew into the ocean and, eventually, into the atmosphere, trapping more heat and warming the planet.
In short, according to this hypothesis, the ice sheets would eventually grow large enough to initiate their own destruction, refilling the oceans. It was a radical idea that has stirred debate.
In an interview, Tolstoy said mounting evidence from the seabed suggested that the volcanic ridges were “exquisitely sensitive” to slight changes in stress, making them open to a variety of celestial influences. Scientists say such factors might one day enhance their understanding of why Earth’s climate has varied so markedly over the ages, improving their computer models and forecasts.
The undersea observatory, by scrutinizing hundreds of ridge features, promises to help scientists address such riddles.
It sits atop the Juan de Fuca Ridge. The volcanic spreading center — more than 300 miles long — lies in a slanted line off the West Coast, from British Columbia to Oregon. The observatory is divided into two parts. Canada operates the northern one and the United States the southern one, part of a larger program known as the Ocean Observatories Initiative.
All told, it cost roughly $500 million — far less than the next generation of optical telescopes under construction around the globe. The National Science Foundation, the federal government’s big funder of basic science, paid for the American part.
Together, the two sites feature more than 1,000 miles of cables, dozens of junction boxes and hundreds of sensors.
Instruments on the seabed include tilt meters, cameras, seismometers, temperature gauges, hydrophones, chemical probes, pressure sensors and fluid samplers. Also, mobile platforms crawl up and down long moorings to take readings higher in the water column. The observatory’s main cables run ashore at Port Alberni, on Vancouver Island, and Pacific City, Oregon.
“We have the most advanced cabled observatory on any volcano in the world’s oceans,” said Deborah S. Kelley, a scientist at the University of Washington who directs the American segment. “There’ll be lots of discoveries.”
Life at 250 degrees
Kelley joined Fornari of Woods Hole and three other marine scientists to compile a photographic atlas that summarises what scientists have learned so far about the hidden world.
“Discovering the Deep,” published in May by Cambridge University Press, is filled with hundreds of images of alien creatures as well as volcanic towers belching clouds of superheated water rich in metals and minerals. It profiles more than a dozen hot spots around the globe, including those on the Juan de Fuca Ridge, home to Godzilla.
Oceanographers, the book says, have discovered vast swarms of unusually sturdy microbes thriving in dark volcanic waters as hot as 250 degrees — hotter than most boiling water on land.
Looking to the future, the authors describe the observatory and its importance for seeing the ocean from within. The investigations, they conclude, “are still in their infancy.”
--c.2016 New York Times News Service