Printed from The Discovery of Hydrothermal Vents - 25th Anniversary CD-ROM ©2002 Woods Hole Oceanographic Institution
|TRAIL OF DISCOVERY: 1972 - The Trail Gets Hot|
Wheres the best place to search for vents?
|In search of more evidenceSouthtow
The trail began in 1972 when scientists returned to the Galápagos Rift aboard Scripps R/V Thomas Washington. The expedition, called Southtow, was part of the International Decade of Ocean Exploration (IDOE). All the research cruises that led to the discovery of hydrothermal vents were funded by the IDOE.
Scientists on the Southtow expedition detected several signs of hydrothermal circulation in seafloor crust, including:
curious seafloor mounds
slightly elevated water temperatures above the seafloor
intriguing patterns of heat flowing through seafloor sediments
micro-earthquakes below the seafloor
|Deep-Tow finds seafloor mounds|
Scripps scientists and engineers led by Fred Spiess had built a deep-sea sonar and camera system called Deep-Tow. They were largely funded by the U.S. Navy, which wanted to develop equipment that could be rushed to sea to conduct searches on the seafloor. The Navy was motivated by the tragic loss in 1963 of the nuclear submarine Thresher, which sank along with its 127-member crew in 2,500 meters (8,250 feet) of water and could not be found quickly.
Deep-Tow also proved to be a very useful tool for scientific investigations. It was one of the first deep-submergence vehicles used by civilian scientists, and it collected data that led to many important discoveries. Deep-Tow is a big metal fish that is towed near the seafloor by a long cable attached to a surface ship. The fish is packed with instruments, including underwater cameras, magnetometers, and sonars. The cable transmits data back to scientists on board the ship.
On the Southtow expedition, Deep-Tows camera found curious, roughly circular mounds sticking out of seafloor sediments about 18 to 36 kilometers (10 to 20 miles) south of the Galápagos Rifts volcanic valley, near latitude 86°W. The mounds were 4.5 to 23 meters (15 to 75 feet) high and 18 to 45 meters (60 to 150 feet) in diameter. Many were crusted with minerals. Their shape and composition indicated that they were deposits formed by hot, mineral-rich fluids circulating in top layers of the ocean crust.
|Telltale heat and mini-quakes
Using Deep-Tow, Southtow scientists measured water temperatures just above the seafloor and found they were a few tenths of a degree higher than normal seawater. This was slight but important evidence of hydrothermal activity.
The measurements of the heat flowing in seafloor sediments showed a curious patternthe heat flow was higher in some areas and cooler in others. To explain this, David Williams and Richard Von Herzen of Woods Hole Oceanographic Institution theorized that hot fluids were rising out of the high heat-flow areas and cold seawater was sinking down into the low heat-flow areas. This pattern of circulating hot and cold fluids is called hydrothermal circulationfrom the Greek words hydros (water) and thermos (heat).
During Southtow, scientists also used instruments called sonobuoys. These devices were developed during World War II to listen for submarines, but they were sensitive enough to detect earthquakes beneath the seafloor.
Using sonobuoys, Ken Macdonald, then a Woods Hole graduate student and now a professor at the University of California, Santa Barbara, detected bursts of small seafloor earthquakes over several dayssometimes as many as 80 per hour. These micro-earthquakes seemed to be occurring in the same area where bottom-water temperatures were slightly higher.
Then Macdonald saw something he had never seen beforeor since. Floating on the surface were lots of dead fish. They were a kind of fish that only lived at great depths near the seafloor.
Soon, all these clues would fall into place. The micro-quakes were creating seafloor cracks that set the stage for hydrothermal circulation. In the same location where Macdonald detected the micro-quakes, scientists five years later would discover a lush community of seafloor life that they would call the Garden of Eden.
|1974 - Project FAMOUS|
|The Birth of a Project
Two years after humans landed on the moon, the time had come to try to send humans to the seafloor. In 1971, Xavier Le Pichon, head of the French Centre National pour lExploitation des Oceans (CNEXO) wrote a letter to Woods Hole geologist Ken Emery and proposed a joint U.S.-French expedition to explore the mid-ocean ridge with human-occupied submersibles.
Few research submersibles existed at the time. The French had the 200-ton bathyscaphe Archimède and were building a smaller diving saucer called Cyana. The U.S. had the Navy-owned, 15-ton Alvin, developed by engineers at Woods Hole. Alvin was only seven years old and still being tested to see what it could do.
Robert Ballard, Emerys former graduate student, replied enthusiastically to the idea for a joint French-American expedition to explore the Mid-Atlantic Ridge. But it needed support and funding from U.S. earth scientists.
|Were submersibles worth the expense?
In 1972, the U.S. National Academy of Sciences convened a meeting of international earth scientists at Princeton University to discuss the proposed expedition. At the time, many scientists had doubts about how useful submersibles might be. The new submersibles had not really been fully tested in the field. Could they withstand the difficulties of deep-sea work? The submersibles also could not cover much ground in the dark depths. Would the information they collected be worth the big price to operate them? Many scientists preferred to devote limited funding to other research pursuits.
In the end, the major decision-makers in the community of oceanographers agreed to fund a research program that was called Project FAMOUS (French-American Mid-Ocean Undersea Study). As the meeting came to a close, Maurice Ewing, one of the giants of oceanography, wagged his finger in Bob Ballards face. If you fail, Ewing told Ballard, well melt down Alvins pressure sphere into titanium paper clips.
|A full-scale effort to lay the groundwork
The preliminary work (for Project FAMOUS) resembled the kind of planning, detailed study, simulation, and training that goes on before a major space mission, wrote Bob Ballard in his book The Eternal Darkness (Princeton University Press, 2000).
Alvins steel sphere, which enclosed its human occupants, was replaced with a titanium sphere in 1973. It could withstand twice as much pressure and extended Alvins diving range from 6,000 to 12,000 feet. Pilots and scientists received special diving training.
The target area for Project FAMOUS was about 9,000 feet deep on a section of the Mid-Atlantic Ridge, between 36°N and 37°N, nearly 400 miles southwest of the Azores Islands. Starting in 1972, an aircraft carrying a magnetic sensor flew over this region of the ocean, James R. Heirtzler of Woods Hole, the U.S. leader of Project FAMOUS, wrote in National Geographic magazine. The sea floor was remapped by normal research ship echo-sounders. Then narrow-beam echo sounders on U.S. Navy and French hydrographic ships refined the bottom charts. Britains R.R.S. Discovery brought a seven-ton side-scan sonar system dubbed Gloria and Scripps Institution of Oceanography provided a special Deep-Tow package.
Scientists aboard ships conducting preliminary work for Project FAMOUS also used floating sonobuoys and instruments lowered to the seafloor to detect sound waves from earthquakes. Sound waves recorded by these devices revealed the hidden structure of rock layers in the ocean crust below the seafloor.
|New tools for an historic mission
For this historic expedition, the U.S. Navy mapped the FAMOUS target area with its powerful and top-secret Sing Around Sonar System (SASS)the first time oceanographers gained access to such detailed seafloor data.
The U.S. Naval Research Laboratory also sent out the U.S.N.S. Mizar with LIBEC (LIght BEhind Camera), a deep-sea photography system built after the submarine Threshers tragic sinking. LIBEC suspended high-intensity electronic flash lamps well above the ocean bottom, making it possible to shoot 120-foot-wide sections of the seafloor.
Woods Hole built a deep-towed camera sled called ANGUS (Acoustic Navigated Geological Undersea Surveyor) specifically for Project FAMOUS.
LIBEC collected 5,250 seafloor photos, which were fitted together and laid across the floor of a Navy gymnasium in Washington, D.C. Scientists wandered over the giant jigsaw puzzle of photos to get their first glimpse of conditions they would encounter on the seafloor.
In the summer of 1973, Archimède made seven reconnaissance dives to the ridge, bringing back rock samples and close-up photographs. Project FAMOUS was ready to go.
|Down to the seafloor in submersibles
In June of 1974, the FAMOUS fleet met in the Azores. Archimède was towed by the French ship Marcel le Bihan. Cyana was on the deck of Le Noirot. Alvin (named after its early champion, WHOI scientist Allyn Vine) was aboard its mother ship R/V Lulu (named after Vines mother). Woods Holes R/V Knorr towed R/V Lulu.In position to drill a core of the seafloor was D/V Glomar Challenger, a converted oil drilling ship recently commissioned by the National Science Foundation for the Deep Sea Drilling Project.
For the first time in history, scientists descended to the bottom of the sea to explore a mid-ocean ridge. They descended between the steep, 5,000-foot ridge flanks into a rift valley as deep as the Grand Canyon. They saw for the first time the narrow zone where magma oozed through seafloor cracks, paving the seafloor and creating new crustand by this process, spreading the North American and European tectonic plates apart.
Alvin made 17 dives and spent 81 hours on the seafloor. Archimède and Cyana completed 27 dives. Scientists used these submersibles to collect 100,000 photos and 3,000 pounds of rock samples, including evidence of manganese and iron deposits. They proved that submersibles could effectively explore the dark, tortuous, volcanic seafloor. They gave geologists the ability to investigate and map unknown terrain on the seafloormuch the way geologists always did on land.
The explorers discovered vast fields of seafloor lava, but they found no evidence of hydrothermal vents.
|Stuck at the bottom of the sea!
Where were the hydrothermal vents that scientists had predicted they would find on the seafloor? Project FAMOUS continued searching during its second year of operation.
In the summer of 1975, Alvin dove with scientists Bill Bryan of Woods Hole and Jim Moore of the U.S. Geological Survey aboard. The pilot was Jack Donnelly.
The seafloor they drove over had many wide cracks, including a fissure that was wider than Alvin. They could not resist going into it. They proceeded slowly, at the pace of a leisurely walk, with Alvin casting its lights only a short distance into the darkness. They could not tell that the fissure walls were narrowing. Suddenly, Alvin was wedged in the crack.
Donnellys initial attempts to maneuver Alvin out of its tight spot failed. No one could come to the rescue.
It was a really spooky feeling, Bryan said in Victoria Kaharls book Water Baby: The Story of Alvin (Oxford University Press, 1990). We would go up maybe half a meter and feel the sub bump against something. Jack tried everything up, forward, back, and we hit something each time, not knowing what it was. It was as if somebody put a big lid over us.
But Bryan and Moore had taken careful notes of their movements as Alvin entered the crevasse, Kaharl reported. White particles flowing in the water gave them a clue about how Alvin probably drifted in the current. Donnelly essentially retraced his steps backwards to get out.
Were clear and under way again, Donnelly announced from the depths. To the amazement of everyone on the ships, he did not rush to surface. Instead he continued the mission.
Alvin never tried to enter a fissure again, and Project FAMOUS never found a hydrothermal vent.
|1976 - Homing In|
|More clues from the Galápagos
The 1972 Southtow expedition to the Galápagos Rift had uncovered some intriguing evidence for hydrothermal vents, so Scripps scientists, led by Peter Lonsdale and Ray Weiss, returned for another look in May of 1976 aboard R/V Melville.
For this expedition, called Pleiades, the Deep-Tow fish was specially outfitted with new equipment attached to its belly. These included a new sensor to measure water temperature and a rack of bottles to sample deep-sea waters.
The sensor detected a narrow zone of water with temperatures about 0.2°C higher than the surrounding seawater. The spike rose up to 125 feet above the seafloor. Was it a plume of buoyant, venting hydrothermal fluids? Chemical analyses of the fluids collected in the special sampling bottles later indicated that a vent might well be there. The new evidence was exciting, but it was still circumstantial and did not prove the existence of hydrothermal vents.
|Frosted fractures and a pile of clamshells
Deep-Tows cameras also captured photos near a gaping seafloor fissure below the place where the temperature spike was measured. The photos showed rocks that seemed to be frosted with white and bright yellow deposits. At the time, it was difficult to conclude for sure that these were minerals precipitated from hydrothermal vents. They might have been meaningless white spots caused by chemical spills when the old black-and-white film was processed!
Deep-Tow also took photos of a pile of big, long, empty, white clamshells strewn on the seafloor (along with one beer can!) This, too, was curious. But it could have been garbage thrown overboard after a party aboard a ship. The scientists called the site Clambake, and marked the spot with transponders. Transponders transmit sound signals that scientists and deep sea vehicles can home in on to determine their location. The transponders left behind by the Pleiades expedition would allow scientists on subsequent expeditions to find the site again.
|1977 - Astounding Undersea Discoveries|
|The Discovery Cruise Begins
The Southtow and Pleiades expeditions had identified the Galápagos Rift as a prime locale to find hydrothermal vents. Project FAMOUS had proved the ability of submersibles to explore mid-ocean ridges. It was time to take Alvin to the Galapágos.
The Galápagos Hydrothermal Expedition, funded by the National Science Foundation, began on Feb. 8, 1977, with Wood Holes R/V Knorr cruising out of the Panama Canal. It was headed to a likely hydrothermal spot marked the year before by the Pleiades expedition. The target was about 640 kilometers (400 miles) west of Ecuador and 330 kilometers (250 miles) northeast of the Galápagos Islands. As it did for Project FAMOUS, the U.S. Navy had made detailed seafloor maps of the region using its powerful, top-secret SASS sonar system.
The expedition was headed by Richard Von Herzen and Robert Ballard of Woods Hole. The scientific party included Jack Corliss, Jack Dymond, and Louis Gordon of Oregon State University, John Edmond and Tanya Atwater of the Massachusetts Institute of Technology, Tjeerd van Andel of Stanford, and Dave Williams of the U.S. Geological Survey.
It was a team of top-notch geologists, geochemists, and geophysicists hunting for hydrothermal vents. No one imagined any need for a biologist on board.
|Sleepy, Dopey, Bashful and ANGUS
Knorr arrived in the general area of the target site on Feb. 12. It lowered three transponders to the seafloor in a triangular pattern. The three sound beacons would help track the positions of Alvin and ANGUS as they explored the seafloor. The scientists named the three transponders Sleepy, Dopey, and Bashful.
On Feb. 15, ANGUS (Acoustically Navigated Geophysical Underwater System) was lowered to the depths to scout the area. Built at Woods Hole for Project FAMOUS, ANGUS was a 2-ton steel cage. It was equipped with cameras and powerful strobe lights. It had a sensor that could detect water temperatures changes as small as 0.005°C. And it had acoustic transmitters that talked to the transponders so that the equipment could be navigated in the dark depths.
ANGUS was towed behind Knorr on a steel cable that stretched to the ocean bottom. It was towed 4.5 meters (15 feet) above the seafloor. Unlike the more delicate Deep-Tow, ANGUS was designed to survive occasional collisions with rugged terrain. Painted on ANGUSs side was the motto: Takes a Lickin But Keeps on Clickin.
As Knorr fought a 1 1/2-knot current to stay over the target site, ANGUS cruised 2,500 meters (8,250 feet) below, taking a photograph every 10 seconds.
|Watching and waiting
All through the evening of Feb. 15, scientists aboard Knorr tracked ANGUS in the depths below. One person made sure ANGUS stayed at the right height above the seafloor, signaling the winch operator to pull in or let out cable as the seafloor terrain got higher or lower. Another person made sure Knorr didnt drift far from the target, signaling the bridge to adjust as necessary. A third person watched the temperature readings of bottom water that ANGUS was passing throughhoping to see a spike that might mean the discovery of a hydrothermal vent. It was tiring and somewhat boring work.
But then, at just about midnight, ANGUS sent out a signal. It had registered a spike in water temperature. The signal lasted three minutes, then water temperatures returned to a near-freezing 2°C (35.6°F). The scientists carefully noted the time and ANGUSs position when the spike (called a temperature anomaly by scientists) occurred. ANGUS continued its mission through the night.
|Thirteen fateful photos
After 12 hours, ANGUS ran out of film. It had shot 3,000 color photos over 16 kilometers (7.25 miles) of seafloor. When the film was developed, the scientists studied the photos, starting from the first one. They looked at hundreds of photos, frame by frame, until they reached the photos that corresponded with the time when the temperature spike, or anomaly, occurred.
In a 1977 article in Oceanus magazine called Notes on a Major Oceanographic Find, Bob Ballard recalled the surprising findings:
The photograph taken just seconds before the temperature anomaly showed only barren, fresh-looking lava terrain. But for thirteen frames (the length of the anomaly) the lava flow was covered with hundreds of white clams and brown mussel shells. This dense accumulation, never seen before in the deep sea, quickly appeared through a cloud of misty blue water and then disappeared from view. For the remaining 1,500 pictures, the bottom was once again barren of life.
Unlike the piles of empty clamshells found by the Pleiades expedition, these clams were clearly thriving.
|Entering another world
Within hours of the startling clam discovery, R/V Lulu with Alvin on board arrived on the scene. The Alvin technical team prepared the submersible, and scientists eagerly awaited the dive at sunrise the next morningFeb. 17. It was Alvin dive No. 713. Jack Donnelly was the pilot. Jack Corliss and Tjeerd van Andel were the scientific observers.
Guided by Sleepy, Dopey, and Bashful, Alvin used the acoustic beacons to zero in on the area where ANGUS had photographed the clams. But when they reached their target coordinates, Ballard wrote in Oceanus, Alvin and its three-man crew entered another world. Coming out of small cracks cutting across the lava terrain was warm, shimmering water that quickly turned cloudy blue as manganese and other chemicals in solution began to precipitate out of the warm water and were deposited on the lava surface, where they formed a brown stain.
Alvins temperature sensors measured water temperatures of 8°C (46°F) at the bottom of the sea. The first hydrothermal vent had been discovered.
But even more interesting was the presence of a dense biological community living in and around the hydrothermal vents, Ballard wrote in Oceanus. White clamsup 30 centimeters (1 foot) longclustered in an area about 50 meters (165 feet) across.
Observing the scene from Alvins viewports, Corliss talked by acoustic telephone to his graduate student Debra Stakes, who was aboard Lulu.
Isnt the deep ocean supposed to be like a desert? Corliss asked. When Stakes answered, Yes, Corliss replied: Well, theres all these animals down here.
|The Garden of Eden
The scientists called the area that Corliss, van Andel, and Donnelly found Clambake 1. But later dives in Alvin discovered four other vent sites with other thriving communities of life. The scientists gave playful names to each one.
Aside from the big white clams, Clambake 1 had brown mussels, many white crabs, and a purple octopus, which probably preyed on other animals at the vent.
Soon the scientists found Clambake 2, where all the clams were dead. This was thought to be the site found the year before by the Pleiades expedition.
The Dandelion Patch had small, never-seen-before, orange animals that resembledyou guessed itdandelions. The Oyster Bed vent site had no oysters (but, remember, geologistsnot biologistswere doing the naming!).
Finally, the scientists came upon a vent site filled with tall, 1 1/2-foot-high, white-stalked tubeworms with bright red tops. Swaying in the water, they looked like a field of flowers swaying in the wind. Water temperatures here reached a balmy 17°C (63°F). The scientists called this site The Garden of Eden.
|A Foul-smelling Clue
The scientists on board Knorr were astonished by the discovery of life thriving without sunlight on the seafloor. They were eager to figure out what the organisms were eating.
But we were not biologists. We were supposed to be finding warm water. Ballard wrote in his book The Eternal Darkness.
The scientists never imagined finding so much life on the seafloor, so they had no reason to stock the ship with lots of chemicals to preserve biological specimens. They stored specimens of clams and other seafloor animals retrieved by Alvin in a small amount of formaldehyde that one student had brought. Then they used the closest thing to formaldehyde that they had on boardsome strong Russian vodka bought in Panama. But there was not nearly enough to preserve all the specimens.
What were these newly discovered organisms feeding on? Water samples from the vents obtained by Alvin soon provided a powerful clue. As chemists drew the first water sample, the smell of rotten eggs filled the lab. Crew members and scientists rushed to open portholes. The water was full of hydrogen sulfide.
|It was like Columbus
A whole lot of things sort of fell into place, said John Edmond, a geochemist from MIT, in Victoria Kaharls book Water Baby. About halfway into the cruise, we realized that regular seawater was mixing with something. It was a unique solution I had never seen before.
We all started jumping up and down. We were dancing off the walls. It was chaos. It was so completely new and unexpected that everyone was fighting to dive (in Alvin). There was so much to learn. It was a discovery cruise. It was like Columbus.
In the years since vents were discovered at Galápagos, scientists have determined that sulfate, which is abundant in seawater, is converted into hydrogen sulfide as the seawater circulates in the ocean crust. The cloudy blue color that the scientists had noted in the water near the vents was a sign of sulfur. Bacteria and other microorganisms use the hydrogen sulfide in the hydrothermal fluids to live and grow. Higher organisms fed on these bacteria.
This deep-sea food chain, which was unknown before 1977, did not require the energy or processes on which most life on Earth depended: sunlight and photosynthesis.
|A scientific scoop.
Unlike the Apollo flight to the moon, the extraordinary Galápagos Hydrothermal Expedition was not watched by millions. Only one newspaper reporter was aboardDavid Perlman of the San Francisco Chronicle. He had a science journalists dream. He scooped everyone else by publishing a series of exclusive stories on a scientific discovery that changed the world.
I had my trusty Olivetti (portable typewriter) along with meyesterday's version of a laptop! Perlman said. So I typed my pieces, and the Knorr radio operator used a Xerox telecopier scan and transmitted each one on the days I wrote via the ships single-sideband radio to Woods Hole, where the obliging PR folk generously forwarded them on to The Chroniclevia Western Union, if I recall correctly.
In one of his stories, published on March 9, 1977, Perlman wrote this about of the expeditions scientists:
They have pinpointed geysers of hot water venting from fissure in fresh lava and sending warm plumes of brine shimmering upward into the near-freezing lower levels of the sea.
They have found rich clusters of living organisms, basking in the warmth of the geysers
They have discovered fresh lava that was poured out onto the sea bottom in ropes and wrinkles, sheet-like pavements and bulbous pillowssqueezed or erupted from the hot, semi-molten material of the deep earths interior mantle beneath the crust.
When these findings are all analyzed in detail they are bound to revolutionize many theories about the deep ocean floor.
The headline for this article was Astounding Undersea Discoveries. Newspaper headlines can sometimes be sensational. This headline certainly wasbut it was also absolutely true.
|Spring 1979 - Oases of Exotic Life|
|Biologists get their first
look at the vents
Scientists had hoped to find hydrothermal vents on the 1977 Galápagos Rift expedition. No one had expected to find lush communities of vent life, so there were no deep-sea biologists on the 1977 cruise. Biologists were bursting with eagerness to investigate these extraordinary deep-sea oases for themselves. But it took nearly two years to mount a return expedition.
In 1979, the National Science Foundation sponsored Galápagos expeditions using Woods Holes R/V Lulu and Alvin, and R/V Gillis, operated by the University of Miami. The chief scientist was J. Frederick Grassle, then a scientist at Woods Hole Oceanographic Institution, now director of the Institute of Marine and Coastal Sciences at Rutgers University. Grassle organized a team of biologists from many institutions. Their goal was to examine how animals thrive in an environment that seemed so harsh.
For this historic cruise, the scientists built special instruments to collect samples of microorganisms and larger animals at the vents. They made experimental devices to learn how the animals were eating and breathing.
To hold the new equipment, a new basket was installed in the front of Alvin. It also got a second manipulator (it had only one left arm before) to help carry out all the sampling the biologists hoped to do. A new, one-of-a-kind, deep-sea movie camera and special underwater lights were installed for filming by the National Geographic Society. National Geographic created an award-winning documentary called Dive to the Edge of Creation.
We would subject the newly discovered communities to the full arsenal of techniques available to modern biology, Grassle wrote in a 1998 article in Oceanus.
|A parade of strange creatures
Nothing could diminish the excitement of seeing the animals for the first time, Grassle wrote in Oceanus. And nothing could prepare them for what they found.
On each of its dives, Alvins front basket and cameras captured a remarkable variety of animals that never had been seen before: unknown mussels, anemones, whelks, limpets, featherduster worms, snails, lobsters, brittle stars, and blind white crabs. One crustacean seemed to have teeth on the end of eyestalks, which scientists speculated were used to scrape food off rocks. A new species of giant white clams with blood-red flesh was given the scientific name magnifica. The delicate, orange, dandelion-looking creature seen on the 1977 cruise turned out to be called a siphonophorea cousin of the Portuguese man-of-war. Alvin technicians fashioned a special dandelion-catching container, but the siphonophore quickly disintegrated after it was fetched to the surface. Its body was adapted to much higher pressure at the seafloor.
At a newly found vent site called Rose Garden, scientists found red-tipped tubeworms that were an astonishing 8-feet tall. Aboard ship, they found that the tubeworms had no mouth to take in food and no guts to digest food!
Literally every organism that came up was something that was unknown to science up until that time, said Richard Lutz, then a post-doctoral scientist at Yale, now a professor at Rutgers University. It made it terribly exciting. Anything that came (up) on that basket was a new discovery.
|Life without light
This rich abundance of animals depended on the warm fluids flowing out of the seafloor.
To live and grow on land, animals use carbon from plants or animals that they eat, and oxygen from the air. At the seafloor, vent animals get their oxygen from seawater. In fact, scientists discovered that the giant clams and tubeworms were such a rich red color because their blood contained hemoglobinthe same molecule that transports oxygen in human blood and makes it red.
So what do the vent animals eat to get the carbon they need to grow? They either eat other vents animals, as the crabs do, or they eat the smaller life at the base of the vent food chainmicroorganisms.
The 1979 Galápagos expedition collected a huge variety of bacteria in the vent waters. Woods Hole biologist Holger Jannasch proved that these bacteria used hydrogen sulfide from vent fluids to take the carbon from carbon dioxide, a gas dissolved in seawater. They convert this carbon into organic carbon, which they can use as food.
Plants do the same thing, using carbon dioxide from air and sunlight as energy, in a process called photosynthesis. In the sunless depths, microorganisms create organic carbon using chemicals for their energy source, a process called chemosynthesis.
The sulfide-rich fluids streaming from the vents nourish an abundant supply of microorganisms, which feed an abundance of animals. Who could have imagined that the dark, cold seafloor would be one of the most fertile places on Earth?
|A major discovery of the 20th century
Woods Hole biologist Holger Jannasch was aboard the 1979 Galápagos expedition and summed it up this way in an article in the Annual Review of Microbiology*:
In the spring of 1979after geologists had discovered dense populations of strange new animals clustered around hydrothermal vents in an area north of the Galápagos Islandsa group of biologists took Alvin back to the same site.
It was an overwhelming experience to fly, 2,550 meters deep, over dense beds of large mussels or even larger (up to 30 centimeters long) white clams, or stands of hundreds of snow-white tubeworms (up to two meters long) crowned with feather-like blood-red plumes.
We were struck by the thought, and its fundamental implications, that here solar energy, which is so prevalent in running life on our planet, appears to be largely replaced by terrestrial energy chemolithoautotrophic bacteria taking over the role of green plants. This was a powerful new concept and, in my mind, one of the major biological discoveries of the 20th century.
* Vol. 51 © 1997 by Annual Reviews.
|Summer 1979 - The Smoking Gun|
Fresh from its epic dives to examine the new-found communities of life around the Galápagos Rift vents, Alvin headed north aboard R/V/ Lulu in April 1979. They joined a U.S.-French expedition that was exploring another section of the mid-ocean ridge called the East Pacific Rise. The site was 1,800 miles north of the Galápagos Rift, just beyond the mouth of the Gulf of California at latitude 21°N. The U.S. group was led by Scripps scientists Fred Spiess and Ken Macdonald on board R/V Melville.
The year before, the French had done scouting work in the area. The submersible Cyana, a veteran of Project FAMOUS, dove into the valley of the rift. Scientists on board Cyana did not see any hydrothermal vents, but they did collect many rock samples. One rock looked like a long tube and had glistening crystals. But the unusual specimen was among hundreds that were collected. So it was not closely analyzed until months later.
The analysis showed that the rock was made of sphalerite (zinc sulfide). The specimen was full of metalsmostly zinc, but also iron and copper, and traces of lead and silver. That was intriguing, because to make a mineral such as sphalerite, you need extremely hot watermuch hotter than the 23°C. (73°F) fluids measured at the Galápagos Rift.
|Superheated water at freezing depths
On April 21, 1979, Alvin dove in search of hydrothermal vents. Bill Normark of the U.S. Geological Survey and Thierry Juteau, a French volcanologistst, were the scientific observers. The pilot was Dudley Foster. He followed a trail of white clams on the seafloor. By now, everyone knew they would likely lead to vents.
Suddenly, the scientists came upon something no human had ever seen before. A tall spire of rock, about six feet tall, was sticking out of the seafloor. A jet of black fluid spewed out of the toplike smoke out of a chimney. Foster said it looked like smoke belching out of the smokestack of a steaming locomotive.
Foster approached to take a closer look. Hot, black fluids rushed powerfully upward from the chimney-like rock. It created an updraft that made it harder to steer Alvin. Foster knocked into the chimney. It crumbled, making a wider hole that let out a billowing cloud of black smoke. It became harder to see.
Using Alvins manipulator arm, Foster grabbed a probe to measure the temperature of the fluids. The reading inside Alvins sphere zoomed as high as it could goto 32.7°C (91°F). The scientists thought it was mistake and tried again. Again, the temperature reading shot up to the limit.
By now, Foster wanted to get out of the black cloud and moved on to another vent. He didnt even bother to take a temperature reading because he assumed the probe wasnt working properly.
|Smoke and minerals
When Alvin surfaced on April 21, 1979, Alvin engineer Jim Akens went to see what went wrong with the temperature probe that he had built. To his surprise, he found that the probes plastic tip had melted. That type of plastic melted at temperatures of 180°C (356° F)!
Alvins viewports were made of the same plastic. The viewports had been only a few feet away from the same hot fluids that melted the temperature probe!
Akens made a new probe that could measure higher temperatures. Scientists in Alvin used it to measure black-smoker hydrothermal vent fluids that reached 350°C (662°F). This was the temperature that MIT geochemist Edmonds had said was possible after he analyzed the lower-temperature hydrothermal fluids from the 1977 cruise. But most people could not easily believe it.
Temperatures of 350°C are hot enough to cause chemical reactions that extract metals from ocean crust rocks and dissolve the metals into hydrothermal fluids. When the superheated fluids hit cold, oxygen-rich seawater, the metals dissolved in the fluids come out of solution (or precipitate). Fluids erupting out of the vents become filled with dark metal particlescreating the illusion of smoke.
Precipitating minerals form blacker-smoker chimneys that can grow very tall. The tallest one found so far was a structure on the Juan de Fuca Ridge, which scientists called Godzilla. It reached 16 stories high before it toppled over.
The year of 1979 was a turning point for hydrothermal vent discovery and research. At Galápagos, hydrothermal vents were shown to be a warm womb that nourished an amazing diversity of life in the dark depths. At 21°N, scientists discovered black smoker chimneys spewing scalding hot fluids for the first time. They saw that hydrothermal vents were also great furnaces, where many of Earths great ore deposits were made.