The History of Woods Hole's Deep Submergence Program
Robert D. Ballard
The Institute for Exploration, Mystic, Connecticut
Since its arrival at the Woods Hole Oceanographic Institution in June 1964, the manned submersible Alvin has gone from a scientific oddity to an accepted research tool. Over its 35-year history, the deep submergence program at Woods Hole has experienced four distinct phases. Its initial design and introduction into the oceanographic community was driven, like all new paradigms, by a small core of scientists and engineers who saw the unique contribution that a manned presence on the ocean floor could make to marine research. The turning point in the acceptance of manned submersibles came on the heels of the theory of plate tectonics and the first manned exploration of the Mid-Atlantic Ridge during Project FAMOUS (French-American Mid-Ocean Undersea Study) in 1974. What led to the final acceptance of manned submersibles were the discoveries in 1977 and 1979 of hydrothermal vents and high-temperature ''black smokers." Since that time, the Alvin program at Woods Hole has matured into a highly reliable and productive diving program fully integrated into a series of long-term research programs. Most recently, the manned submersible at Woods Hole has been merged with its newly developed remotely operated vehicle program.
THE EARLY YEARS OF ALVIN
The first phase of deep submergence started in the late 1950s when the bathyscaphs Trieste and Archimede began taking scientists into the abyssal depths of the world's oceans.
In 1956, after several years of bathyscaph operations by the Swiss and French, Jacques Piccard, son of the bathyscaph designer August Piccard, spent 100 days in America, traveling to all the major centers of oceanographic research trying to sell them on the virtues of the bathyscaph. To his pleasant surprise, he found many sympathetic ears eager to enter the world he and only a few others had visited. The visit came to a conclusive end at a National Academy of Sciences meeting in Washington when Piccard and Robert Dietz, an early supporter of the bathyscaph, presented papers on its potential value to deep-sea research.
Convinced of its merits, Willard Bascom spearheaded a resolution that read: "The careful design and repeated testing of the bathyscaph have clearly demonstrated the technical feasibility of operating manned vehicles safely at great depths in the ocean. The scientific implications of this capability are far reaching. We, as individuals interested in the scientific exploration of the deep sea, wish to go on record as favoring the immediate initiation of a national program, aimed at obtaining for the United States undersea vehicles capable of transporting men and their instruments to the great depths of the oceans." This resolution was followed in Feb-mary 1957 with a contract between Piccard and the Office of Naval Research (ONR) to conduct a series of dives in the Tyrrhenian Sea off Naples so that American scientists could carefully evaluate its potential.
From July to October, Trieste made 26 dives carrying acousticians, biologists, geologists, physicists, VIPs, and naval personnel down to depths of 3,200 m. The U.S. Navy and ONR were now convinced that the bathyscaph held great promise and they wanted to support its future.
At the time, the Naval Electronics Laboratory in San Diego, California, was a hub of activity for naval research. There, a close bond existed between the operational navy and the oceanographic community. The largest oceanographic institute, Scripps Institution of Oceanography, was just a short distance away in La Jolla. For that reason, the Navy decided to base the Trieste in San Diego, with the goal
of using the bathyscaph to dive to the bottom of Challenger Deep in the Marianas Trench in 1960 as a part of Project NEKTON. Trieste's historic dive to the bottom of Challenger Deep in 1960 clearly demonstrated that man could penetrate the oceans to even their deepest depths. But the bathyscaph was large and difficult to operate and maintain in the open sea many miles from its home base.
Global coverage required the capability to carry the diving craft aboard a surface support ship that could transit at high speeds to the dive site and between dives bring the craft back aboard for maintenance and repairs. This dream of a tiny portable submersible was, in fact, already beginning to take shape even before Trieste's 1960 diving campaign in the mind of a young French officer, Jacques Cousteau, who had witnessed the first test dive of the bathyscaph FNRS-2 off Dakar in 1948. Cousteau' s Souscoup was the first modem deep submersible to be built. However, its diving capability was limited to 300 m, far too shallow for the oceanographic community.
Just as Cousteau's experience with the French bathyscaph lead to the creation of the Souscoup, the Americans diving on the Trieste began to think about a similar modem submersible small enough to be carried aboard a mother ship.
No sooner had Trieste completed its deep dive in 1960, than the San Diego group including Andy Rechnitzer, Don Walsh, and Larry Schumaker began to dream of its replacement. Listening to these discussions was Harold "Bud" Froehlich, a General Mills engineer who had built Trieste' s mechanical arm. Soon he was circulating the designs of a small prototype submersible he called the Seapup to anyone who was interested.
While this teapot began to boil, another spark was being lit on the East Coast. Charles B. "Swede" Momsen, Jr., the Chief of Undersea Warfare in ONR, the same organization that had sponsored Trieste, had received a proposal from J. Louis Reynolds of the Reynolds Metals Company to design and build an all-aluminum submersible called the Aluminaut. Momsen was a decorated submarine commander during World War II and was comfortable with its large design. The only problem was that ONR was not in the business of building submarines; it could rent one if Mornsen could find scientists interested in using it. Ironically, when Momsen went to the Scripps Institution of Oceanography in San Diego where Trieste was now based, he received a cold reception to his idea.
This was not the case when he approached scientists at the Woods Hole Oceanographic Institution (WHOI) on Cape Cod, Massachusetts. In particular, Allyn Vine and WHOI Director Dr. Paul Fye welcomed the idea and offered Woods Hole as Aluminaut's home base. What followed, however, was a long and drawn out series of discussions between ONR, Woods Hole, and J. Louis Reynolds. The sticking point was the ultimate ownership of the Aluminaut. Reynolds wanted to maintain title, while ONR wanted the Navy to own it with eventual ownership going to Woods Hole.
As time ticked on, the engineers Woods Hole had hired to operate the Aluminaut program began to question its design. They had the same concerns Cousteau had. Aluminaut was to be 51 feet long and carry six people. More importantly, like the bathyscaphs, it had to be towed out to sea and could not be brought aboard its mother ship for maintenance and repairs.
Finally after three years and four months of nonstop negotiations, an impasse was reached, and it became clear to Paul Fye that something new had to be tried. The only problem was that others in Washington were trying to pry loose the funds Swede Momsen had been squirreling away for the project.
Knowing other companies were eager to enter the deep-submersible game, Momsen acted quickly and authorized Woods Hole to request bids to build a submersible for the institution. The specifications that went out were not for a submersible like the Aluminaut but for a much smaller design, strangely similar to Bud Froehlich's Seapup.
Seven companies were sent the request for bid: Froehlich's General Mills, Lockheed, General Dynamic's Electric Boat Division, General Motors, North American Aviation, Philco, and Pratt Whitney Aircraft. Although four of these companies would eventually build their own deep submersibles, only two submitted bids to build what would become Alvin; General Mills and North American Aviation. General Mills was the ultimate winner since the Navy felt it was more committed to the project. Ironically, shortly after winning the bid, General Mills sold its division to Litton Industries, which finally built and delivered Alvin to Woods Hole in the summer of 1964.
Alvin could initially dive to 1,830 m, far deeper than the Souscoup , but clearly not to the abyssal depths of the bathyscaphs. As a result, the early users of Alvin were midwater biologists and scientists working on the continental margin.
Frank Manheim, a geologist with the U.S. Geological Survey at Woods Hole, was eager to extend his research on marine snow that had been pioneered by the Japanese. For years, Manheim had filtered seawater obtained from lowered instruments and weighed the dried filters to determine how much marine snow existed per unit volume of the ocean.
When he repeated this procedure using water collected from Alvin, he realized that this method of quantifying marine snow was not accurate. On his dive, he had seen a heavy snowfall, but the weight of his filters drawn from water collected by Alvin indicated otherwise. In the mud cores he brought up, there was little organic material. This seemed to indicate that the animals were extremely adept at food gathering; they were consuming the fine rain of organic material as soon as it hit bottom.
Studies of the deep scattering layers, also begun by the bathyscaph, continued using Alvin. Woods Hole biologists Richard Backus and Jim Craddock used Alvin and its highly sensitive CTFM sonar to study the layer. With the lights
turned off they homed in on a good-sized blob on the scope. When they turned on the lights, they were surrounded by thousands and thousands of lantern fish. The fish were pointed and moving in all directions—"a fantastic aggregation not a school." The biologists had thought that photophores, which were usually on the underside of the fish, were meant to shine down and blind predators. But the photophores of these lantern fish were aimed in every conceivable direction. Rarely had their nets captured a lantern fish; and yet Alvin's net brought up 744 of them on one dive. Small collecting nets mounted on Alvin were also successfully used near the bottom by Woods Hole biologist George Grice, who discovered 18 new species of copepods on one dive.
While benthic biologists took advantage of Alvin's ability to carry out difficult manipulative tasks in the deep sea, marine geologists took advantage of its high maneuverability. K.O. Emery and a geology group he had formed at Woods Hole began using Alvin to explore the submarine canyons off the Northeast coast. Here a great series of canyons cut across an extensive continental shelf. But geologists were not only interested in understanding the origin of submarine canyons and the role they played in transporting sediments across the continental shelf to the deep sea, these canyons also provided them with knowledge about Earth's recent history.
The continental shelf in most parts of the world consists of horizontal layers of sedimentary rock laid down one layer on top of another over millions of years. As submarine canyons form, they cut down into these layers, exposing in their walls the geochronology or geologic history of the region. Using the submersible's ability to maneuver, geologists were able to sample these outcrops and add further detail to the recent stratigraphic history of the continental shelf.
Similar investigations were carried out in the Straits of Florida and the Bahama Banks, as well as submerged terraces such as the Blake Plateau. Instead of studying sedimentary layers of rock deposited by river outflow, geologists were able to investigate layer upon layer of limestone formed in place by coral growth and erosion.
But submarine canyons and steep vertical scarps were not the only geologic features on the continental margins explored in the 1960s using manned submersibles. A popular winter diving area for Alvin was the Tongue of the Ocean between New Providence and Andros Islands in the Bahamas. The vertical walls of this 2000-m trough consists of fossiliferous limestone providing geologists with the opportunity to look back into the early carbonate geology of this region.
In addition to using Alvin to study the natural history beneath the sea, in one case it was used to investigate human activity on the continental shelf during the Ice Age. Of particular interest was the work dealing with submerged shorelines by K.O. Emery, Robert McMaster, and Richard Edwards. The Ice Age led to the dramatic lowering of sea level on a worldwide basis: 15,000 years ago, off the East Coast of the United States, it was between 70 and 130 meters below its present position.
As sea level rose with the melting of the continental ice sheets, a series of ancient shorelines was created and later flooded, forming relic features on the present continental shelf. During an Alvin dive in 1967, Edwards and Emery encountered a submerged beach and oyster reef formed 8,000 to 10,000 years ago off Chesapeake Bay. On the ridge top inland from the submerged beach they found oyster shells thought to be kitchen middens created by the early humans that must have inhabited this area at the time. Although little has been done since, the continental shelves of the world may prove to contain significant archaeological sites awaiting future discovery.
Just as the scientific community was gaining confidence in Alvin's ability to dive routinely and safely, disaster struck. At the end of its 1968 dive season, Alvin was in the process of being launched on dive 307 when suddenly its forward cables broke, dropping the submersible into the sea. Quick action saved the crew and passenger, but Alvin disappeared beneath the waves, falling 1,585 m to the ocean floor. There it remained until 1969 when a heroic salvage operation returned it to Woods Hole.
As engineers accessed the damage done during her 10 months underwater a startling discovery was made (Jannasch and Wissen, 1970).
Alvin broke surface again in September 1969 after resting almost one year on the ocean floor. In the excitement over her successful recovery, the oceanographers almost overlooked the striking outcome of Alvin degradation experiment: the food in the box lunch was practically untouched by decay, although containing the usual amount of bacteria.
The broth, although being the most perishable material. was perfectly palatable. Four of us are living proof of this fact. The apples exhibited a pickled appearance. But the way the salt water had penetrated into the fruit tissue indicated that the membrane functions were hardly affected. Enzymes were still active, and the acidity of the fruit juice was not different from that of a fresh apple. The bread and meat appeared almost fresh except for being soaked with seawater.
In conclusion, the food recovered from Alvin after ten months of exposure to deep-sea conditions exhibited a degree of preservation that, in the case of fruit, equaled that of careful storage, and in the case of starches and proteins appeared to surpass by far that of normal refrigeration.
The ocean floor as a giant refrigerator was an image that continued to be reinforced as the deep sea began to yield more and more of its preserved human history. The same year that Alvin was lost, she dove on a World War II Hellcat fighter plane that was ditched by its pilot in 1944. Resting in 1,524 m of water, it was in excellent condition.
In marked contrast to these images of a frozen deep ocean setting in which biological processes move at a snail's pace is the work by Dr. Ruth Turner of Harvard's Museum of Comparative Zoology. In 1972, Dr. Turner used Alvin to
place a series of wooden panels into the bottom at a depth of 1,830 m. After 104 days of exposure, several were recovered (Turner, 1973):
The wood was so weakened as a result of the activity of wood-boring bivalve mollusks, that it began to fall apart while being picked up by the mechanical arm of Alvin. The minute openings of their burrows covered the surface, averaging about 150 per square centimeter ....
High population densities, high reproductive rates, early maturity, rapid growth, apparent ease of dispersal, and the ability to utilize a transient habitat make these wood borers classic examples of opportunistic species, the first recorded for the deep sea.
The site at which Dr. Turner carried out her initial wood borers experiments was known as DOS #1 for Deep Ocean Station number one, the first long-term bottom station established in the deep sea. Although others have subsequently been established, scientists continue to return to this site even today. The site was selected in 1971 as the first permanent bottom station because it lay along a line between Woods Hole and Bermuda, where benthic biologists had conducted deep-sea dredging operations for more than six years.
In fact, the first dive Alvin made for science took place in 1,785 m of water off Bermuda on July 17, 1966 with biologist Robert Hessler aboard. Hessler wanted to learn more about the benthic world he had been studying for years using deep-sea dredge hauls (Ballard, in press):
I was awed by the tremendous vertical precepts, and I finally understood why we had so much difficulty ever taking any samples from that area ....
That dive really taught me something. From then on whenever I lowered a dredge into the ocean, I could close my eyes and picture what the bottom of the deep sea looked like.
Hessler and benthic biologist Howard Sanders were impressed by the diversity of life in the deep ocean sediments. A student of Sanders, Fred Grassle, began to use Alvin to quantify these early observations. Returning to DOS #1, Grassle disturbed small patches of occupied seafloor with No. 2 fuel oil and fertilizer and left trays of sterilized, uninhabited mud to measure its colonization. Others put down small instrumented jars to measure respiration and found that deep-sea animals needed ten to a hundred times less oxygen than their shallow-water counterparts. Microbiologists, like Holger Jannasch, injected organic material into the seafloor as the field of benthic biology moved into a more quantitative phase in its history.
PROJECT FAMOUS-THE FIRST COMPREHENSIVE USE OF MANNED SUBMERSIBLES IN A MAJOR SCIENCE PROGRAM
In 1971, manned submersibles entered a new phase in their application that would eventually dominate their use. Prior to this time, submersibles were used primarily by biologists and geologists in sedimentary settings,; ranging from soft mud bottoms to calcium carbonate terrains,,. But in 1971, Alvin began a comprehensive mapping program in the Gulf of Maine. Unlike most continental margin settings, which consist of thick sedimentary wedges, the Gulf of Maine is a seaward continuation of the Appalachian Mountain range. Instead of soft sediments, it consists of crystalline igneous and metamorphic rock dating back hundreds of millions of years.
To carefully map this area required the submersible to implement traditional field mapping techniques used by geologists on land. The creation of such maps requires the collection of geologic information in three dimensions, including not only surface exposure but subsurface structure and composition. First and foremost was the need for detailed bathymetric maps of a region measuring more than 100,000 km2 at a contour interval of at least 20 m or better. Fortunately, extensive bathymetric data existed for this area.
Such bathymetric data provided a picture of the regional morphology but not its internal structure and composition. To provide this information required extensive surveying using seismic profiling techniques. The database used in this study included tens of thousands of kilometers of seismic survey lines collected over a period of more than eight years prior to and during the actual diving program. This coverage led to the creation of a three-dimensional picture of not only the regional bedrock geology but also the sedimentary basins contained within it and equally important where the bedrock geology was exposed as outcrops.
Once such outcrops were pinpointed samples had to be collected to determine the bedrock composition. Unfortunately, the entire Gulf of Maine had undergone extensive glaciation during the Ice Age and the retreating glaciers covered the area with glacial deposits of varying thickness, deposits that bear no relationship to the underlying rock formations. As a result, traditional dredging operations could not be carried out since they almost always resulted in the collection of glacial erratics instead of the more difficult to sample bedrock outcrops. Here, careful coordination was required between surface seismic profiling activities needed to pinpoint bedrock outcrops and subsequent ,:lives by Alvin to sample them. This mapping program in the Gulf of Maine set the stage for a new phase in the use of Alvin.
Although research programs carried out by scientists around the world began in the 1950s and continue to this day using manned submersibles, the 1970s marked a fundamental change in their use. This shift in focus came as technological improvements in deep submergence engineering made it possible for manned submersibles to go much deeper than before. Principal among these improvements was the fabrication of higher-strength steel and titanium pressure spheres. Two vehicle programs led the way, one in the United States and the other in France. America's Alvin was modified to carry a titanium pressure hull with an initial operating depth of 3,050 m, while France's CNEXO (Centre
National pour L'Exploitation de Oceans) brought into service the new deep submersible Cyana with a similar depth capability.
Associated with this shift in emphasis came an entirely different group of scientists who began pondering the very origin of the ocean floor and the role it played in global geology. In the late 1960s, geophysicists began a revolution in the Earth sciences by advancing a new theory to explain the observed structure of the ocean floor. In so doing, they began to explain the position of the continents rising out of our global sea.
Years earlier, a German meteorologist named Alfred Wegner had advanced what geophysicists at the time regarded as a poorly supported theory. He called it "continental drift" and drew his supporting evidence from the continental land masses. Fitting Africa and South America, he went on to compare their similar interlocking geological features. But unable to explain how continents could actually drift apart, he died in ridicule, and continental drift entered modern geology textbooks not as a unifying theory but as one held up to scorn. Beginning in the 1950s, however, this theory underwent a rebirth as geophysicists began to probe the ocean depths in earnest. Plunging heat-probes into the ocean floor sediments far from land, they were surprised to observe unusually high readings.
Although they were well aware of a central ridge in the middle of the Atlantic Ocean, which the Germans had mapped prior to World War II, it wasn't until after the war that they realized it was seismically active along its entire length. Drs. Bruce Heezen and Maurice Ewing of Columbia University's Lamont Geological Laboratory used the global distribution of earthquakes to propose the existence of a continuous range running through the major ocean basins of the world, which they termed simply the "Mid-Ocean Ridge." Reconnaissance dredging operations followed, which recovered basaltic rock samples along its summit indicating the presence of active volcanism. Various explanations were advanced to explain these observations but the real breakthrough came when Drs. Vine and Matthews published magnetic maps of a segment of the ridge, the Carlsberg Ridge. There for all to see was a systematic series of parallel strips of ocean floor having alternating magnetic polarities. More importantly, they were symmetrical or mirror images of one another, with the line of symmetry being the very center line or axis of the Mid-Ocean Ridge. From these observations came the theory of seafloor spreading later modified to be plate tectonics and Earth scientists "had a new game of chess to play." (P. Hurley, pers. comm.) And play they did.
The formal body of scientists grappling with this revolutionary theory had its roots in the International Council of Scientific Unions. This same body had initiated the International Geophysical Year in 1957 to 1958. By the late 1960s, this interest in plate tectonics was incorporated in the Geodynamics Project, "an international program of research on the dynamics and dynamic history of the earth with emphasis on deep-seated foundations of geological phenomena. This includes investigations related to movements and deformations, past and present, of the lithosphere, and all relevant properties of the earth's interior and especially any evidence for motions at depth." (Ballard, in press).
In late 1971, Dr. K.O. Emery received a letter from Dr. Xavier Le Pichon, a student of Dr. Maurice Ewing and a strong supporter of plate tectonics. Le Pichon had been urged to write to Dr. Emery by Dr. Charles "Chuck" Drake, who like Dr. Le Pichon, was a graduate of Lamont and Chairman of the Geodynamics Project. Dr. Drake had made an earlier dive in the Puerto Rico Trench aboard the French bathyscaph Archimede and saw its potential as a geological mapping tool.
Dr. Le Pichon, now in charge of a major new marine laboratory in Brest, France, the Centre Oceanologique de Bretagne (COB), wanted to use the Archimede and the new French submersible Cyana to investigate the Mid-Ocean Ridge. But he wanted it to be a joint program between France and the United States. He was keenly aware of Woods Hole's submersible Alvin and knew it was already proving itself as an emerging geological mapping tool. In his letter, Dr. Le Pichon briefly explained what he had in mind—a detailed mapping effort in the Mid-Atlantic Ridge Rift Valley—and asked Dr. Emery if he thought submersibles were up to the challenge and if Emery was interested in joining the program.
In the final draft of the letter sent to Dr. Le Pichon, Dr. Emery strongly supported such a program but declined to participate. Emery was a continental geologist comfortable with its submerged seaward limits, but he was not a "hard rock" geologist who wanted to venture into the Mid-Ocean Ridge. The next logical person for Le Pichon to turn to was Dr. James Heirtzler, chairman of Woods Hole's Department of Geology and Geophysics. Heirtzler was also a Lamont graduate, and although he was not a field geologist, he was a strong advocate of plate tectonics and a pioneer in the field of marine magnetics.
But before such a major program could receive the funding it required, a considerable amount of support within the Earth sciences community was required. France's new CNEXO to which Dr. Le Pichon's laboratory reported could make decisions without significant outside review or approval. This was not the case in the American system and, in particular, the National Science Foundation (NSF). Clearly, NSF was the obvious source of funding for what would eventually be called Project FAMOUS.
Working under the broad umbrella of the Geodynamics Project, Dr. Heirtzler worked with Drs. Drake, A.G. Fisher, Frank Press, and M. Talwani to organize the Mid-Atlantic Ridge Workshop with the official endorsement of the Ocean Science Committee of the National Academy of Sciences. If the program Le Pichon and Heirtzler had in mind was endorsed by the Academy, it was a strong candidate for NSF funding.
The meeting that took place during the week of January 24, 1972, became known as the Princeton Workshop after the Ivy League school where it was held. NSF's International Decade of Ocean Exploration (IDOE) Office provided the financial support for the meeting, which was an obvious good omen for future funding. More than 40 scientific leaders of the Earth sciences community from nations around the world including the United States, France, the United Kingdom, Canada, and the Netherlands attended.
The final report resulting from this workshop entitled Understanding the Mid-Atlantic Ridge—A Comprehensive Program, (NRC, 1972) after numerous formal presentations, much debate, and late night dinners, contained five "high-priority field projects" including the following recommendation:
Interdisciplinary surface ship surveying and sampling on a small scale over critical areas on the Mid-Atlantic Ridge should be followed up in the most critical subareas by more detailed geological and geophysical investigations, using the capabilities of deep-towed vehicles and submersibles.
The report containing this recommendation also contains the following notice:
The study reported herein was undertaken under the aegis of the National Research Council with the express approval of its Governing Board. Such approval indicated that the Board considered that the problem is of national significance, that elucidation or solution of the problem required scientific or technical competence, and that the resources of the NRC were particularly suitable to the conduct of the project.
With this official endorsement for a comprehensive American Mid-Atlantic Ridge program, including the use of manned submersibles, Dr. Heirtzler and others could now move forward in formalizing a major joint program with the French, which would become Project FAMOUS.
Although Project FAMOUS would be best known for its first use of a manned submersible in the Mid-Ocean Ridge, it did, in fact, involve every major technological tool then being used by marine geophysicists and would set the example for subsequent Mid-Ocean Ridge investigations. The area selected for this intense investigation of the Mid-Atlantic Ridge was between 36 and 37° N latitude for a long list of reasons. We wanted to be in a region of favorable weather and near a good logistical support base, which in this case was Ponta Delgada in the Azores, but far enough away from its "hotspot activity" to ensure that we were investigating "a typical spreading segment" of the ridge.
The chief scientists of Project FAMOUS were, to no one's surprise, Drs. Jim Heirtzler and Xavier Le Pichon. Prior to the actual joint diving operations, which took place in the summer of 1974, they published the goals of the project in an issue of Geology (Heirtzler and Le Pichon, 1974):
Among questions that we hope to answer are the following: What is the detailed age distribution of the surface rocks in this zone? What is the relative importance of primary constructional features and secondary tectonic ones in shaping the morphology? Is the structure of the boundary zone steady state? And if not, to what extent? What is the distribution of the different types of igneous rocks with respect to the tectonic and volcanic features within the zone? Are large portions of the oceanic crust exposed along the obviously faulted scarps of the Rift Valley? What is the thickness and exact nature of the layer at the origin of the Vine and Matthews magnetic lineations? Are there metamorphic rocks (zeolites, greenschist, or even amphibolites facies) within the zone? What is their distribution with respect to the different tectonic features? Many other questions can be asked concerning the tectonics of the transform-fault area. One of the most important is how localized is the zone of shearing? Is there really a transform fault or a zone of transform faulting? What is the distribution of the ultrabasic rocks that occur within this zone? Is there volcanic activity within the transform fault? And so forth.
To address this long list of questions using traditional field mapping techniques, first and foremost required excellent topographic maps. This was particularly true for the Mid-Ocean Ridge given its complex morphology, but also because its morphology was a direct reflection of the volcanic and tectonic processes taking place within its rifted inner valley.
The first dives into the rift valley in 1973 used the French bathyscaph Archimede. In all, seven dives were made by the Archimede covering a 5-km2 area of the central high and the adjacent eastern marginal high. The central high was found primarily to be a constructional volcanic feature not significantly altered by subsequent tectonics. The central zone of extrusive lava flows was found to be bounded to the east, in the area the Archimede investigated, by steep vertical scarps up to 100 m in height thought to be volcanic flow fronts.
These preliminary dives clearly revealed that despite the tremendous lateral dimensions of the North American and African crustal plates, the actual zone of injection that includes surface lava flows is extremely narrow and ideally suited to submersible investigation. Had the boundary separating the spreading plates been broad, as reason might have led one to believe, the investigation of such a region by a manned submersible might have been an utter failure.
With these initial promising results, Project FAMOUS moved into its final phase in the summer of 1974 with the coordinated diving programs of the submersibles Alvin and Cyana and the bathyscaph Archimede and continued surface ship studies.
Never before had three deep diving submersibles carried out such a coordinated effort. Having more than one vehicle diving in the area added to the overall safety of the operations as described later, but it also had its drawbacks.
A critical aspect of the FAMOUS dives in the rift valley was a precise knowledge of where the vehicles were at any one time when observations were made, photographs taken,
or important rock samples collected. For this reason, each vehicle had its own network of bottom-moored acoustic transponders. At the end of each dive, we were able to produce an edited plot of the submersible's x-y track across the rift valley floor. Adding the depth and altitude of Alvin along this track, we were able also to produce a bottom depth profile for the dive. Using these two plots and a transcription of the science divers' observations, we were able to produce a series of geological traverses across the rift valley floor. These annotated profiles included a wide range of observations dealing with the various volcanic and tectonic features we observed as well as the sediment cover, which reflected the age of the terrain.
In all, the American submersible Alvin conducted 17 dives, while the combined efforts of the French submersible Cyana and the bathyscaph Archimede completed 27 dives. Each vehicle was assigned to a particular operational area within the inner rift valley and the bounding transform faults. Alvin's work area included a central volcanic high called Mount Pluto and the southern portion of Mount Venus to the north. The Archimede overlapped Alvin's coverage of Mount Venus, working north up the rift valley toward transform fault A, which was the primary operational area for the submersible Cyana.
When the expedition ended and the final results were published in two volumes of the Geological Society of America Bulletin (1977, 1978), our detailed knowledge of the process of seafloor spreading had taken one giant leap forward illustrated by the following text that appeared in Science in 1975 (Ballard et al., 1975):
Observations confirmed that Mt. Venus and Mr. Pluto are the sites of most recent volcanic activity. The flanks of these hills consist of broad, steep-fronted flow lobes with relatively little sediment cover or attached organisms. The flow fronts consist of tubular lava extrusions elongated downslope, resembling in some respects terrestrial pahoehoe lava.
. . . in all traverses from the center of the valley outward to the flanks, we were impressed by the rapid increase in sediment cover and bottom life and by the intense tectonic degradation to which the extrusive lava forms were subjected. Generally, within 300 m of the valley center to the west and within 500 m to the east, most of the delicate extrusive forms had been destroyed, the flows were sliced and offset by numerous faults, and the surfaces were reduced to broken, jumbled lava blocks and extensive talus fans at the base of fault scarps.
In contrast to recent volcanic activity, which appears to be concentrated in a narrow central zone, recent tectonic movement is evident throughout the entire width of the inner rift valley floor. Faults and fissures are numerous, striking 020 degrees parallel to the rift axis.
Intrusive sills and dikes are exposed only at the base of one 300-m scarp on the west wall. Most fault displacements are less than 100 m and expose only breccia, truncated lava pillows and tubes.
In general, faulting appears to be a continuing process, while volcanic activity is episodic.
Simple and logical as these observations may seem, they confirmed the process of seafloor spreading, providing the first systematic documentation of a process that had global significance. Manned submersibles had finally come of age.
On the way back from the FAMOUS research site in the Mid-Atlantic Ridge, the Alvin was used to carry out a series of dives along the New England Seamount Chain, revealing ancient volcanic terrain covered by a thick layer of manganese and phosphorite similar to that encountered on the Blake Plateau.
Although Project FAMOUS was capturing the headlines in the early 1970s, scientists continued to use manned submersibles for their more traditional applications on the continental margins. The benthic biology community continued its studies of wood-boring organisms as well as efforts to quantify the biomass within deep-sea sediments and their rate of recolonization. Spurred on by the sandwich recovered from inside the lost Alvin, scientists expanded their research to include the decomposition of solid organic materials in the deep sea, with an eye toward the implications of using the ocean as a future dump site.
Geologists also continued using manned submersibles to study the carbon stratigraphy of the Bahama Platform, including its potential for hydrocarbon deposits and the occurrence of "lithotherms," deep-water coral structures that trap bottom transported sediments forming long linear ridges beneath the Gulf Stream in the Straits of Florida.
But clearly, Project FAMOUS had ushered in an entirely new phase of scientific use of manned submersibles, in particular, Alvin. Several factors were responsible. The first was the increased diving depth of Alvin from 1,800 to 3,050 m. The second was the integration of the manned submersible into a larger context, namely the lengthy preparation of a research site prior to the actual diving program. This preparation included the collection of detailed bathymetric maps and geologic traverses across the proposed study area using deep-towed vehicles such as Deep Tow and Angus. Most importantly, however, was the emergence of plate tectonics. In the final analysis, manned submersibles were in the right place at the right time.
THE DISCOVERY OF HYDROTHERMAL VENTS AND THE ACCEPTANCE OF ALVIN BY THE SCIENTIFIC ESTATE
For most of the scientists participating in Project FAMOUS, it was an unqualified success. But for one group, it was a bitter disappointment. Dr. Dick Holland had led a team from Harvard and Woods Hole that was keenly interested in finding underwater hot springs along the axis of the
rift valley but failed to do so. Years before, Dr. Clive Lister of the University of Washington observed a deficit of conductive heat release near the Mid-Ocean Ridge, which he argued supported the existence of hot springs within the axis. Scientists speculated that the Mid-Ocean Ridge owes its vertical relief to the fact that it is swollen with heat energy—that the ridge, unlike mountain ranges on land, is in essence a blister on the surface of the Earth.
Since new oceanic crust is being generated along the axis of the Mid-Ocean Ridge, it is by definition the youngest in age and for this reason should be the hottest. As the process of seafloor spreading continues with the injection of new crustal material along the ridge axis, older oceanic crust is pushed to the side, forming two giant diverging geologic conveyor belts carrying crust away from its site of creation. As it is transported away from the ridge axis, the crust slowly cools, and cooling causes the crust to contract. In essence, scientists were saying that the ridge's vertical profile represents a theoretical cooling curve.
If this hypothesis was correct, it should be possible to correlate the amount of heat coming out of the ocean floor with the distance from the ridge axis at which the measurement is made. The farther away from the ridge, the lower the heat probe reading should be. Well, this is exactly what scientists found, except, as Lister pointed out, along the axis itself. Although heat probe measurements made near the axis were high, they weren't as high as they theoretically should have been. A significant amount of heat was missing. What process was taking place along the axis of the ridge that was removing this otherwise uniformly released heat energy?
The only logical answer was hot springs. We all knew that the ridge must be underlain by magma chambers at a relatively shallow depth of 1 to 2 km. We also knew that these magma chambers contain molten rock at a temperature of 1,200 to 1,400°C. During Project FAMOUS, we discovered that the central volcanic terrain was fractured by numerous fissures and faults, which made it very permeable. Clearly, cold bottom waters within the rift valley at a temperature of 3 to 4°C could easily enter the ocean floor and must penetrate to the hot rock region surrounding the magma chambers below.
Once heated and thermally expanded, these highly enriched geothermal fluids should rise back to the surface of the rift valley floor, exiting as hot springs along its axis. But Holland's team had been unable to detect any temperature anomalies within the FAMOUS study area. Either hot springs didn't exist there at the time of the study or they didn't exist at all.
However, a growing group of marine investigators was warming to Lister's theoretical argument favoring the existence of hot springs along the axis of the Mid-Ocean Ridge. Paralleling Lister's geophysical line of reasoning was one emerging from the field of geochemistry. In 1965, Scripps graduate student Jack Corliss was completing his thesis work based upon the analysis of basaltic rock samples dredged from the Mid-Atlantic Ridge. This analysis clearly suggested that seawater was seeping downward into the newly formed ocean floor, penetrating the hot rock surrounding the magma chamber, leaching out various chemicals to form hydrothermal fluids that then flowed back to the surface of the ocean floor. The driving force of this internal circulation system was the buoyancy of the heated fluids and the tremendous geothermal gradient separating the shallow magma chamber from the cold bottom waters within the rift.
In 1975, the year after Project FAMOUS, two scientists following these two different lines of reasoning joined forces to propose an expedition to the Mid-Ocean Ridge using manned submersibles that would put these theories to test. They were Dr. Richard von Herzen formerly of the Scripps Institution of Oceanography and now at Woods Hole and Dr. Jerry van Andel also formerly of Scripps and now at Oregon State University. Van Andel had been Corliss' thesis adviser at Scripps and was well aware of his line of argument suggesting the existence of hot springs along the axis of the ridge. Von Herzen's specialty was heat flow, and he fully understood Lister's line of reasoning. Being at Woods Hole, von Herzen was keenly aware of Alvin's recent successes during Project FAMOUS. More importantly, van Andel had been one of the principal diving scientists during FAMOUS and knew first hand that Alvin was up to the challenge.
The result of this collaboration was a proposal to NSF, which had sponsored the FAMOUS Project. to search for hot springs not in the Atlantic Ocean but in the Pacific along a segment of the Mid-Ocean Ridge called the Galapagos Rift. There were several reasons for picking this site. To begin with, Oregon State University already had a large program in the Pacific called the Nazca Plate Project funded by NSF. Second, the spreading centers in the Pacific were much faster than the spreading center of the Mid-Atlantic Ridge. The faster the spreading rate, the more heat energy was being released along the ridge axis and the greater was the probability of finding hot springs.
During the subsequent cruise in the summer of 1976, a variety of instruments were used to investigate the inner rift valley of the Galapagos Rift, including sediment traps, water chemistry samplers, and the Deep Tow system from Scripps, which has a side-scan sonar and bottom camera and lighting unit. To everyone's satisfaction, the expedition succeeded in detecting temperature anomalies within the near bottom waters of the rift, which were marked by a long-term acoustic transponder.
The stage was now set for the final phrase of the program, a dive series by Alvin to pinpoint the suspected hot springs. This was scheduled to take place during the winter of 1977. Leadership for this effort was transferred from van Andel to Corliss when van Andel accepted an appointment at Stanford University. But concern over Corliss' lack of diving experience led van Andel to ask me to rake Corliss on
our Cayman Trough expedition, which was about to take place during the winter of 1976.
The Cayman Trough program had two primary purposes. The first was to use the submersible Alvin, the bathyscaph Trieste II, and the towed camera system Angus to investigate a small spreading center situated inside the transform fault system separating the North American Plate from the Caribbean Plate. Known as a "leaky transform fault," this boundary had a slight opening motion that led to the formation of an east-to-west spreading center bordered to the north and south by the steep walls of the Cayman Trough. The result was one of deepest spreading centers in the world, with the central volcanic axis occurring at a depth of 6,100 meters. The walls of the fault scarps within the trough also provided an opportunity for petrologists to obtain samples of the oceanic crust using the submersible Alvin.
The second reason for the Cayman Trough program was to maintain the momentum created by the success of the FAMOUS Project, while others like van Andel had an opportunity to define diving programs for funding given the scientific community's new positive attitude about submersibles.
The Cayman Trough investigation provided Corliss with an excellent opportunity to learn first-hand how to conduct a sophisticated research program using manned submersibles. It also provided him with the opportunity to make his first submersible dive.
By the time the Galapagos Hydrothermal Expedition got underway in February 1977, I had been asked to be co-chief scientist of the expedition with Dick von Herzen—not because I was a major scientific leader for this research program but because of my experience at conducting submersible programs. The real scientists behind the program were Jack Corliss and Jack Dymond from Oregon State University and John Edmond from the Massachusetts Institute of Technology. Jerry van Andel was also on the expedition, primarily to help these inexperienced scientists with the actual diving program to be carried out aboard Alvin's support ship Lulu.
The expedition's destination was a point 640 kilometers west of the coast of Ecuador, along the rift that separates the fast-spreading Cocos and Nazca plates in the Pacific Ocean. Our plan was to concentrate on the sites where seafloor temperature anomalies recorded by the earlier Scripps-Oregon State-Woods Hole expedition had suggested the existence of hydrothermal vents.
Woods Hole's research vessel Knorr, with Lulu under tow, began the expedition at Rodman Naval Base in the Panama Canal, but after several days at sea, it was decided to break the tow and let the two ships proceed under separate power to the dive site. This way, the faster Knorr could arrive ahead of Lulu, install a network of acoustic transponders within the rift valley, and conduct some preliminary reconnaissance runs with the towed camera system Angus.
The year before, I had been successful in convincing the U.S. Navy to conduct a detailed Sound Acoustic Surveillance System (SASS) sonar mapping effort of the Galapagos Rift dive area similar to the survey it had conducted in the FAMOUS area. The FAMOUS expedition and the 1976 program in the Cayman Trough had set a new standard for bathymetric detail that all future submersible diving programs would now seek to emulate.
Once the ship arrived in the area, Knorr's echo-sounder was used to collect a series of profiles perpendicular to the rift axis. Using this information, the buoy left the previous year by Corliss, and satellite navigation, we did our best to tie our present location to the estimated location of the thermal anomalies detected the year before.
Woods Hole's Angus camera sled was now lowered into the rift from the research vessel Knorr. Angus was equipped not only to take thousands of color pictures but also to register temperature changes as minute as one five-hundredth of a degree Celsius. Angus's sensitive thermistor at first recorded no variations in the near-freezing temperatures just meters above the ocean floor. Then, as the first day's run neared its halfway point in the early evening of February 15, recorders on board Knorr received an acoustically telemetered signal from Angus , revealing a sudden spike in water temperature, lasting less than three minutes. Since the time and temperature data were precisely keyed to the frames of film exposed by Angus's cameras as it canvassed the bottom, we were able to review the pictures taken at the exact moment of the temperature spike. But first, Angus had to be hauled back to the surface and the film developed.
All were eager for the first visual evidence of the hypothesized thermal vents—but nothing could have prepared us for what Angus had photographed, one and a half miles beneath the surface. The 122-m-long roll of color film revealed a bed of clams—hundreds of clams clustered in a small area on the lava floor of the rift—thriving as if they were in an environment no more hostile than a sunny mudflat on the New England coast. We couldn't help but wonder what these large clams were doing in such numbers at that depth, in that eternal darkness.
The next step in the research plan called for the deployment of Alvin to whatever promising sites Angus might reveal. It was February 16 when Lulu with Alvin aboard arrived in the dive area, and we lost no time in getting the submersible into the water at sunrise the next day, February 17.
After a descent lasting an hour and a half, pilot Jack Donnelly brought Jack Corliss and Jerry van Andel to a point less than 275 m from the clam beds and began the drive along the lava floor to the site. Along the way, the bottom appeared as might have been expected: fresh but relatively barren lava flows.
But when Alvin reached its goal, the scene the scientists observed through the viewports was remarkably different. Water that Alvin's sensors measured at 12°C, shimmered up from cracks in the lava flows and turned a cloudy blue as manganese and other minerals, which had been carried from
deep within the vents, precipitated in the cooler surroundings. Clams, giant specimens, measuring a foot or more in length, along with similarly outsized brown mussels, appeared to be bathed by the simmering water. Alvin's robotic arm, which had been expected to grasp only rock samples from the bottom of the Galapagos Rift, now was pressed into service to grasp samples from this most remarkable community of shellfish. When we planned this cruise, our thoughts had been so far from biology that we had brought no preserving medium along. Some of these samples thus made the trip back to shore immersed in vodka.
Over the coming days, the expedition' s researchers took turns scouring the rift for similar signs of life. With guidance from Angus, these rovings in Alvin bore rich rewards. We eventually identified five sites that teemed, or had recently teemed, with creatures as bizarre as they had been unexpected. We termed our initial find "Clambake I" and also located a site we called "Clambake II," where a change in conditions had killed off the big bivalves and left only a midden of shells. The "Oyster Bed" was our label for a patch of mussels, miss-identified as oysters°our flawed attempts at taxonomy went temporarily unchallenged, since there were no biologists along on the expedition°and another site was dubbed the "Dandelion Patch,'' because it was home to a population of hitherto unknown animals resembling bright yellow dandelions, attached to the bottom not by stalks but by delicate fibers. Finally, there was the "Garden of Eden," lushest and most varied of these strange oases. Here were the dandelions, along with white crabs, limpets, small pink fish, and clusters of vivid red worms that protruded from their own long, stalk-like white tubes. The tube of a specimen later brought to the surface measured more than two meters in length, with the animal itself filling more than half of its elongated tube.
The obvious question in everyone's mind was what enabled these colonies of creatures to flourish at such depths, in an atmosphere totally devoid of sunlight? The answer quickly came, on board Knorr, with the analysis of water samples taken by Alvin at the vents surrounded by the oases. The first thing noticed, when the sample containers collected by Alvin were opened, was a pervading odor of rotten eggs: hydrogen sulfide. This was the clue that enabled us to piece together the chemical and biological processes that made possible the huge clams, tube worms, and other life forms in such high concentrations.
The earlier suggestions of Lister had been shown to be true. The deep fissures in the floor of the rift allowed cold seawater to penetrate Earth' s crust, down to the level of hot, newly formed layers of rock surrounding the magma chamber. The temperature of the water rose as it flowed deeper, and its chemical composition changed. The seawater exchanged some of its chemicals with the subsurface rock and leached out others. The sulfate in the water was changed to hydrogen sulfide°hence the telltale smell in the lab. Finally, the heated water rose back to the seafloor through other fissures in the crust and raised the ambient temperature of the vent oases to the surprising levels recorded by Alvin.
Living inside the macrofauna of clams and tube worms were hydrogen sulfide-oxidizing bacteria that formed the basis of this unique food chain. In the case of the clams, the available nutrients were abundant enough to lead to gigantism. Clambake II, in the light of this analysis, appeared to have been an oasis chilled and starved into extinction as the recycling of seawater through the vents had ceased for some unknown reason.
We had discovered something new upon Earth. Prior to our investigation of the hydrothermal vents along the axis of the Galapagos Rift, all forms of life had been assumed to be dependent upon photosynthesis, the process by which sunlight is metabolized to sustain the growth of plants and animals. Even the holothurian, living at great depths in a sunless world, depends for its survival upon organic material that drifts down from the sunlit surface. But within the vent field, for the first time, was evidence of a community of animals subsisting on a process of chemosynthesis, beginning with the metabolizing of hydrogen sulfide by microorganisms. They were, after all, creatures that needed no sunlight at all for survival and that owed their existence to the warmth and chemical sustenance of Earth itself.
Two years later in 1979, marine biologist Fred Grassle and I co-led a second expedition to the undersea oases of the Galapagos Rift. Fourteen other biologists accompanied us— this time, there would be no relying on vodka for preserving specimens. We also brought a film crew from the National Geographic Society, which chronicled our discoveries in the television special "Dive to the Edge of Creation." This time, the challenge we faced was quite different from our 1977 task. Then, we were looking for hydrothermal vents and had no idea of the oases. Now, we were trying to locate the same sites we had visited before, in a place where there were no identifying landmarks either above or beneath the surface.
As before, we deployed Angus as our eyes and temperature sensor prior to a manned investigation in Alvin. Reviewing the thousands of frames exposed by Angus's cameras on the sled's first run along the rift floor, we began to resign ourselves to a long search. Then, with about four frames to go, we found what we were looking for. Angus had photographed a clutch of our mysterious dandelions, and we knew we were in the right spot.
Taking our turns in Alvin, we explored a string of new vents and their surrounding oases, including the largest discovered on either of the two expeditions—an otherworldly habitat for tube worms 2 to 3 m long. And with our complement of biologists and biochemists, we were able to achieve a far more sophisticated understanding of the processes involved in sustaining the creatures of the oases and to make an attempt at classifying them.
Beyond a doubt, it was the chemosynthesized nutrients that made the oases possible. The warmth of the water itself was not a primary factor; there are animals that survive the
near-freezing temperatures even at the deepest reaches of the sea, fed by organic material drifting down from the surface. Here, though, the secret of abundant life was a cornucopia of locally derived nutrients. The concentration of food at the oases far surpasses the amounts available elsewhere on the sea bottom. One of our colleagues estimated that the waters surrounding the vents contain 300 to 500 times the nutrients found at nearby sites lacking the benefit of the mineral-rich flow from the vents.
The driving force behind the unique vent communities is the rapid growth of the chemoautotrophic bacteria that are able to use the dissolved oxygen and carbon dioxide present in oceanic bottom waters to oxidize the reduced inorganic compounds (i.e., H2S, S, S2O3, NH4, and NO2) dissolved in the hydrothermal fluids coming out of the vent openings. This chemosynthesis process has been known by microbiologists for many years, but it wasn't until the discovery of the Galapagos Rift hydrothermal vents in 1977 that scientists realized it could form the basis of an entire ecosystem.
Although this process takes place in total darkness, it is still tied to the sunlit surface. For the chemosynthetic process to occur, the bacteria require free oxygen to oxidize the reduced inorganic compounds coming out of the vents. This free oxygen has been generated by green plants as a by-product of the photosynthetic process. An interesting question is: What would happen if the sun suddenly turned off? Clearly, the vent communities would continue to thrive until the free oxygen in seawater was exhausted. But even after that point in time, anaerobic chemosynthesis would persist.
There are many forms of bacteria involved in the chemosynthetic process, which occurs in three basic settings: (1) within the subterranean vent system cutting deep into the volcanic terrain, (2) in large microbial mats covering its surface, and (3) within the internal structure of various symbiotic organisms living around the vent openings. The benthic animals that make up the vent communities have a fascinating strategy for survival. We now know that hydrothermal vents are highly ephemeral or short-lived. They turn on and off in a matter of a few years or tens of years. As a result, vent animals have an "r-type" survival strategy. They are able to settle quickly out of the water when a vent turns on, grow fast, reproduce early, and easily disperse their offspring into the water column to find new vent settings.
The vent communities discovered in 1977 by chemists and geologists and revisited in 1979 by biologists are characterized by large organisms situated in diffuse zonations centered around discrete vent openings where the temperature is the hottest. In the case of the Galapagos vents, the maximum exiting temperature measured was 17°C and the dominant macroorganism living near the vent opening is the giant red tube worm Riftia pachyptila. These spectacular organisms form large clusters or hedges standing 2 to 3 m in height. One of the large populations was termed the "Rose Garden." Without eyes, mouth, or digestive tract, the worm's red tip or obturaculum absorbs food and oxygen from the water by means of hundreds of thousands of tiny tentacles arranged on flaps on the exposed portions of its body. These are the critical compounds needed by the bacteria living inside its body for the chemosynthetic process. Since these ingredients come from both the anaerobic vent fluids (i.e., hydrogen sulfide) and the ambient bottom water (i.e., oxygen and carbon dioxide), the worms position their red tips in the area of mixing just above the vent opening, clustering in thickets to direct the vent fluids up past the tip of the tubes. Sexually differentiated, they most probably broadcast eggs and sperm into the water.
Living directly inside the vent opening itself are a variety of limpets (i.e., Archaeogastropoda) that are also observed living on the white base of the tube worms. Living in close proximity to the vent openings in some cases are large beds of mussels (Mytilidae) attached to the volcanic substrate, as well as other organisms like the tube worms, by strong byssal threads.
In our investigation of the Galapagos Rift vents communities in 1977, the organisms that I found as impressive as the red tube worms were the giant white clams (Calyptogena magnifica) that covered the fresh lava flows. We commonly saw these clams wedged down inside a small fissure cutting across the volcanic terrain, parallel to the rift valley axis. Their anterior end pointed down and their hinge point up, an ideal feeding position with the hydrothermal fluids flowing up past them. The clams of the rift were noteworthy not only for their gargantuan size, but also for the intense blood-red color of their flesh—as with the tube worms, this coloration is due to a high amount of hemoglobin, the pigment of human blood. In numerous cases, you could see that as the clams grew, their enlarging shells conformed to the jagged outline of the fissure opening, wedging them in place.
This vent species was also a critical indicator of past vent activity. Unlike most vent organisms that quickly vanished after a vent turned off, the large white clam shells persisted for many years before finally being dissolved by the ambient bottom water, which is undersaturated by calcium carbonate. In fact, an inactive vent characterized by a cluster of dissolving clam shells was first seen in a deep-tow survey along the Galapagos Rift in 1976 but was not recognized for its importance until after an active vent was found by Angus and investigated by Alvin in 1977.
Other important organisms living in and around the Galapagos vents are a variety of anemones (Actinarians), brachyuran crabs (Bythograea thermydron), galatheid crabs (Munidopsis), jellyfish called "Dandelions" (i.e., rhodaliid siphonophores), and an highly unusual worm (Enteropneust ) clustered in what resembled piles of "spaghetti." The blind white crabs that frequent the oases and feed upon dead mussels and clams are apparently members of a heretofore unknown crustacean family.
What about the so-called dandelions? Animals despite their plant-like appearance, these turned out to be a new siphonophore, related to the Portuguese man-of-war but
spending their lives attached by their threadlike filaments to the rock formations of the bottom. Each of the creature's "petals," dissection showed, has a different purpose. Some capture microorganisms; others digest them; and still others are involved in reproduction. All surround a buoyant pocket of gas, which allows the animal to bob at the end of its tethers.
As our time on the rift went on, we collected new species of leeches, worms, barnacles, and whelks. We even took away some 200 strains of bacteria, which were brought alive to Woods Hole for whatever clues they might offer to the basis of this remarkable food chain. Throughout our observations—whether they involved the humblest microorganisms or the most extravagantly sized and colored worms and bivalves—we were tantalized by the thought that surely such phenomena could not have been confined by evolution only to this obscure stretch of the Galapagos Rift. At how many other places on the bottom of the oceans do such communities thrive, and how many other yet-unknown species draw life from the interplay of seawater with the steaming, mineral-rich depths of Earth's developing crust?
Before the 1979 return trip to the Galapagos Rift took place, plans were already underway for a major expedition to the East Pacific Rise by many of the same French and American scientists who participated in Project FAMOUS. After Project FAMOUS was completed, the French were eager to conduct another large joint program with the United States on the Mid-Ocean Ridge. Since Project FAMOUS was conducted on a slow-spreading segment of the ridge where the plates are moving apart at a rate of 2.5 cm per year, the French wanted to compare what they had learned about the volcanic and tectonic processes of the Mid-Atlantic Ridge with a faster-spreading ridge in the Pacific Ocean.
Spearheaded by Dr. Jean Francheteau, the French chose the East Pacific Rise (EPR), where the plates separate at a range of 6 to 12 cm per year. Based on a series of studies of the rise conducted by U.S. oceanographers, the French selected a segment of the EPR at 21°N latitude, at a spot off the Mexican coast where the Pacific and North American plates diverge. As the program took shape, the French asked a number of U.S. scientists, including myself, if we would be interested in such a joint investigation.
While it had been fitting for Woods Hole to play the lead role in Project FAMOUS since the program was conducted in the Atlantic Ocean and involved the use of its submersible Alvin, Woods Hole was not the logical choice for the East Pacific Rise program. The Pacific Ocean was the territory of the Scripps Institution of Oceanography. And since scientists at Scripps had carried out most of the research on the East Pacific Rise on which the French were basing their study, it was decided at a workshop held in La Jolla, California, that Scripps would be the lead U.S. institution for this joint program. Dr. Fred Spiess of Scripps would play the role Jim Heirtzler had played during Project FAMOUS.
As with FAMOUS, the French wanted to carry out the first series of dives of the East Pacific Rise using their submersible Cyana and I was invited to participate. This initial dive series was scheduled for February 1978. The French named their phase of the program RITA, for the two transform faults (Rivera and Tamayo) that bounded the spreading segment of the EPR to be investigated. Their plan was similar to the approach they had taken during FAMOUS—to conduct a series of long dive traverses at right angles to the axis of the rise. This meant that they would be diving across time lines, beginning in the center of the rise where young lava is flowing out onto the seafloor and exploring in both directions away from this central zone of injection. They would head east toward the coast of Mexico and the North American plate, and west toward the Pacific Ocean and the Pacific Plate.
The French dive series in 1978 using Cyana at 21°N was highly successful, completing 21 dives. Like the FAMOUS study area, the central volcanic axis was found to be relatively narrow, flanked on either side by older tectonically altered terrain characterized by fissures and small-scale fault scarps. Reconnaissance dives were made between the EPR crest and the Brunhes-Matuyama reversal area 21 km to the west (three dives) and in the Tamayo transform (six dives). The extrusion zone is narrow (0.4 to 1 km), like that of slow-spreading centers. The extension zone, bracketed by a nearly continuous bottom traverse, has a half-width of 7-8 km. The Brunhes-Matuyama area was thus tectonically dead.
In contrast, the extension zone of slow-spreading centers is thought to be wider, although there are no field observations. Hydrothermal activity is demonstrated by colored deposits of rocks, tall cones of variegated deposits, and fields of giant clams (dead). Intense hydrothermal activity is probably a general feature of the EPR in contrast with its scarcity in the FAMOUS rift. Large areas of the young seafloor are covered by pahoehoe flows (sheet flows) and by lakes with pillars, expressing the greater fluidity of EPR extrusives compared with Mid-Atlantic Ridge (MAR) pillows and perhaps reflecting readier access to a larger magma pool.
A fascinating find associated with the East Pacific Rise expedition as well as those to the Galapagos Rift in 1977 dealt with the undersea lava flows encountered along these faster-spreading centers. During Project FAMOUS, the dominant extrusive lava form was an endless variety of pillow lavas, which scientists considered to be the classic underwater flow form. But when submersibles began diving in the faster-spreading centers of the Pacific, we encountered an entirely different type of lava feature termed "sheet flows." Unlike pillow lavas, which consist of a network of small lava tubes intertwined like a pile of spaghetti with individual "pillows" budding off from lava tubes, sheet flows form vast lakes or pools of molten lava. Fluctuations in the level of these lakes—caused by drainback into the magma chamber deep beneath the ocean floor—are indi
cated by "bathtub" rings around the perimeter of the lake. Clearly, the faster spreading rates associated with the East Pacific Rise and Galapagos Rift are commonly characterized by high volumes of sheet flows that flood large areas of the inner rift valley.
Another strange feature found within these lava lakes is lava pillars standing within the lake that resemble "tree molds," which are common in active volcanic areas on land such as those in Hawaii. When lava flows into a forested area on land, the molten rock is quenched when it comes into contact with the moist surface of the tree. Although the tree is consumed by fire, leaving only remnants of charcoal, a hollow cylindrical column of rock is formed; whose interior lining commonly preserves an imprint of the tree's bark. When the eruptive cycle ends and lava flows back into the magma chamber, a forest of tree molds is left standing as mute evidence of the forest that once stood there.
The lava pillars discovered within the lava lakes of the East Pacific Rise and Galapagos Rift are formed in a similar way. Prior to an eruptive cycle along a given spreading segment of the rift axis, the older lava terrain is characterized by a complex and dense network of fissures that are thoroughly permeated with seawater. When the eruptive cycle begins, sheet flows issue from only a few of the fissures within the fractured floor and spread out laterally covering a much larger area. As a result, the remaining water-filled fissures are capped by the flows, trapping large volumes of water beneath them. This seawater becomes heated and seeks to escape upward. Passing through the layer of molten lava contained in the lakes within the rift, this superheated water rapidly quenches the lava through which it passes. Hollow vertical chimneys of solidified rock form within the lava lake. As the level of lake drops, these chimneys remain as pillars of rock commonly supporting a thin canopy or crust of quenched lava running around the perimeter of the once-liquid lava lake. In appearance, it resembles "Yorkshire pudding."
Although the French dive series in 1978 did not result in the discovery of any active hydrothermal vents, it did locate one inactive site characterized by an accumulation of large white clam shells that were badly dissolved. During another dive, the scientist aboard Cyana came across some unusual chimneys on the older flanking volcanic terrain, which were sampled. After later analysis onshore, this sample was found to be 100% sphalerite or zinc sulfide containing 10 percent iron, 50 percent zinc, and 1 percent copper, with trace concentrations of lead and silver. The French had discovered an ore deposit on the East Pacific Rise that must have been formed under very high temperature conditions.
Although the highest temperature measured at the vent sites along the Galapagos Rift in 1977 was 23°C, laboratory analyses of the collected water samples suggested that the initial starting temperature of the hydrothermal fluids as they left the reactive zone around the magma chamber was between 350 and 400°C. Clearly, the discovery in 1978 of high-temperature mineral deposits by the French indicated that high exiting temperatures for hydrothermal vents might actually be possible.
The American phase of the joint U.S.-French investigation of the East Pacific Rise took place in late 1979. At the time, we were just beginning to understand how narrowly confined the central volcanic axis of the Mid-Ocean Ridge truly was, given the significant lateral dimensions of the crustal plates it was creating.
Some of the scientists participating in the expedition, particularly those from Scripps, were convinced that the zone of volcanic extrusion was wide and that there were significant areas of off-axis eruptions taking place several kilometers from the central rift valley. These scientists, headed up by Dr. Fred Spiess, were interested in the seismic velocity, density, porosity, and permeability of the upper oceanic crust. They wanted to know about the fine-scale motions of the seafloor on a time scale of months to years. To this end, they also wanted to use Alvin to carry out scientific experiments and instrument deployments, rather than serve as a vehicle for qualitative observation. Previous Deep Tow lowerings had located a reasonably flat area to the west of the central axis known as "Tortilla Flats," where they hoped to locate fresh lava flows using their Deep Tow system and then visit the site with the submersible Alvin.
Deep Tow's primary sensors were a side-scan sonar, temperature probe, and magnetometer: indirect geophysical devices designed to paint a broad regional picture of the sea-floor. Although it did have a black-and-white slow scan television camera and a black-and-white still camera, it spent little time in close visual contact with the bottom. Day after day passed as Deep Tow surveyed the area, but no active venting was located as the so-called Tortilla Flats proved to be old in age, covered by a thick blanket of sediments.
Another team aboard the Melville, including Jean Francheteau and me, was convinced that the zone of volcanic activity was narrowly confined along the central axis and that it was within this narrow zone of recent volcanism that active venting would be found. During our 1977 and 1979 expeditions to the Galapagos Rift, we had discovered that the active hydrothermal vents lay along a straight line apparently associated with the eruptive fissure responsible for the youngest flows within the rift valley. Once a vent was found, it became relatively easy to find additional vents along any particular fissure system by simply driving along the fissure, parallel to the rift axis.
Our tool for this search effort was Angus, and we patiently awaited our chance to go into the water. Angus, unlike the Deep Tow system, was designed by geologists to remain in constant contact with the bottom. It was designed to take a head-on collision with the rugged volcanic terrain and survive, making it possible to enter the narrow axial graben bound on either side by steep fault scarps.
After extensive Deep Tow coverage failed to locate any hydrothermal activity, Angus was finally permitted to enter
the water. Unlike the traverses made by submersibles that are perpendicular to the axis of the rift, Angus' traverses were basically parallel to the axis. This was not based on geological reasoning but on operational necessity. Traverses perpendicular to the axis were the most desired. But Angus needed to be within a few meters of the ocean floor to obtain the high quality of color images we sought. Since the fault scarps bounding the rift to either side run parallel to the axis, Angus tow lines were best run in the same direction to avoid countless collisions with the bottom. It was also along this same strike that we felt active vents would be found. As a result, the first Angus trackline resembled a slalom run, as the vehicle was towed from side to side down the strike of what we hoped was the central volcanic axis.
No sooner had Angus begun its first run before the temperature sensor on the vehicle indicated it had passed through an active vent area. Repeating its performance in the Galapagos Rift, the sled was recovered so that the color film could be processed in the portable laboratory that had been brought on the expedition for that purpose. But a review of the color film taken across the vent field revealed a scene different from those observed along the axis of the Galapagos Rift. Initially the scene was the same, as frame after frame showed the vehicle passing over a young volcanic terrain characterized by a fresh glassy lava surface.
The first indication of an approaching vent was not a rise in temperature but the appearance of small white Galathea crabs dotting the otherwise barren flows. Quickly this gradient of crabs increased, giving way to the larger and more densely packed sessile organisms, in particular, large white clams so typical of the Galapagos Rift vent fields. As the center of the field was approached, "milky" water could be seen along with an increase in the amount of particles in the water. But unlike the Galapagos vents, the center of the vent was not covered with tube worms and large clams. Instead, we saw a large yellowish-brown deposit of sediments largely devoid of life.
The coordinates of this vent site were transmitted by radio from the Melville to Jean Francheteau aboard Alvin's support ship Lulu. Since Alvin and Angus shared a common network of bottom transponders, it was easy to vector Alvin to any site discovered by Angus. Clearly, the role of submersibles was changing with the reconnaissance and regional mapping efforts falling more and more upon towed vehicle systems such as Angus. Towed vehicles had been used for several years to conduct regional mapping programs but it wasn't until 1977 to 1979 that joint operations between towed vehicles and manned submersibles became so closely choreographed.
What made this possible was the speed at which the photographic runs conducted by Angus were processed. Not only were tens of thousands of frames of color positive film quickly developed in a portable processing van for immediate viewing, but the edited tracks were also quickly plotted. This provided the geologists onboard with the opportunity to immediately generate detailed annotated traverses across the ocean floor. These traverses were then superimposed over the detailed bathymetric database to produce preliminary geologic maps. Each lowering added more and more detail to the evolving map of the area. The goal of this process was to space the Angus lines at just the right interval to permit the correlation of observations from one line to the next but not so closely as to produce highly redundant and, therefore, wasteful coverage.
On previous programs, a year or more had passed between the collection of towed vehicle data and follow-up dives by the submersible. Or even worse, the submersible conducted its own reconnaissance traverses working independent of towed vehicles. This was certainly the case with Projects FAMOUS and RITA.
On April 21, with the coordinates of an active hydrothermal field as their dive target, Alvin was lowered into the water. Dudley Foster was the pilot on this dive and as he dove over the fresh lava flows he began to see small white crabs on the horizon; he was reminded of similar scenes months before in the Galapagos Rift. But as he entered the vent field, it didn't feel the same. The water was much cloudier than usual. Then suddenly a tall chimney-like spire came into view; belching out its top was a dense black fluid resembling bellowing clouds of smoke. It looked like a steel factory as Alvin maneuvered above it for a closer view. But driving in midwater was proving difficult for Dudley; something was pulling him toward what he now called a "black smoker."
The pulling force proved to be the updraft or chimney effect caused by the rising black fluid. The black smoker was pulling water in from the side. And since Alvin was neutrally buoyant, it was also being pulled toward the smoker. Driving was made even more difficult as Dudley passed over the smoker and visual contact was lost in a thick cloud of black particles. Suddenly, he bumped against the chimney, which fell over like a giant fallen tree.
Ironically, this made the situation much better as the black fluid was now flowing out of the base o f the broken chimney instead of its top. Dudley could new turn on his variable ballast system and take in water, making Alvin negatively buoyant as it slowly landed on the bottom. Using his lift props, he now climbed a gentle mount surrounding the fallen chimney. Clearly, these structures were fragile since the entire mound, which was some ten meters in diameter and a few meters tall, consisted of numerous broken chimneys that had fallen before.
Since he was the first human to see such a feature, chimneys appeared to fall over naturally without the help of submersibles. As he approached the fallen chimney with black fluid flowing out of its base, he could see the chimney was hollow, lined by mineral crystals that reflected in the submersible's lights. Now that the submersible was resting firmly on the bottom, Dudley could bring his manipulator into play. Resting in Alvin's science tray was a temperature
probe attached to a long plastic tube with a "T" handle that Alvin's mechanical arm could easily grasp.
Lifting it from the tray, Dudley rotated the probe to the right and positioned it just above the cloudy vent opening. The temperature readout inside the pressure hull shot up, and when Dudley inserted it inside the vent, it went off scale. Now Dudley grew nervous. The probe had been used in the Galapagos Rift to measure the exiting temperatures of the vents. Never had it risen above 23°C, comfortably within its 100°C range.
Clearly, this vent was "hot," but how hot? Dudley's fears heightened when he removed the probe and found that its plastic holder had completely melted. His first thought was of his forward viewport, which was only a few feet from the vent opening and made of the same material as the melted probe.
This may have represented a major discovery for scientists but it was also very dangerous for submersibles. Dudley slowly pulled back, dropped his ascent weights, and brought the submersible back to the surface. Once safely back on Lulu's cradle, Dudley saw how lucky he had been that day. Inspecting the fiberglass fairing near the lower viewports, Dudley found that the submersible's skin had melted.
The next day, when Francheteau and I dove in Alvin, we were much more cautious when approaching a black smoker, but the thrill was just the same. Francheteau said it best in his wonderful English, "They seem connected to hell itself." This time we were better equipped with a probe that could measure much higher temperatures, in our case, an incredible 350°C or 662°F, hot enough to melt lead, let alone our Plexiglas viewports out of which we were staring in utter amazement. Here in 3,000 meters of water we had visual proof of what geophysicists and geochemists had only theorized. Here also was a crystal clear explanation of what had eluded chemists for centuries, a logical explanation of the ocean' s chemistry.
What Jean and I were watching was part of the same process of recycling seawater that fueled the food chain on the oases of the Galapagos Rift. It was superheated water that was funneling out of the mouths of the chimneys°water blackened by its concentrated solution of minerals from deep within the Earth' s crust. The construction of the chimneys themselves was a testament to the mineral richness of this subterranean broth; as the fountains of returning seawater cooled, they precipitated material that built the flue pipes ever taller.
During the 1977 dives on the Galapagos Rift, we had already seen the effect of hydrothermal vents (in that instance, not full-scale black smokers) on seafloor animal communities. Now, observing the cycling of seawater through the perforated juncture between two crustal plates, we began to speculate upon the broader relationship between the ocean and the crust that they largely conceal. Some scientists have since speculated that all of the water in the seas may seep down into the hot lower crust and back up through the vents, over a cycle lasting 10 million to 20 million years. As we saw in the black smokers, the minerals carried back up to the seafloor precipitate and harden into ore deposits°one explanation, perhaps, for the presence of such deposits on dry land that was once covered by the ocean.
Following the discovery of high-temperature hydrothermal vents on the East Pacific Rise at 21°N by the towed camera system Angus and the submersible Alvin, all hell broke loose. Not only did this discovery prove that the vent communities in the Galapagos Rift were not unique, it also demonstrated that the precipitation of polymetallic minerals within the vent system could result in the exiting of high-temperature fluids directly from the ocean floor and the surface accumulation of important mineral assemblages.
The potential consequences of these discoveries had a profound impact upon many fields of marine research, in particular the fields of biology, chemistry, geology, and geophysics. Just as the theory of plate tectonics had mobilized the Earth sciences in the early 1960s, the discovery of hydrothermal vents in the Galapagos Rift and East Pacific Rise mobilized the field of oceanography. All of a sudden, a large number of marine scientists who had never been in manned submersibles or been interested in the spreading axis of the Mid-Ocean Ridge were submitting proposals to their various funding agencies to investigate deep-sea vents. Some used the importance of these discoveries in basic research to justify their requests, while others argued the commercial potential of the mineral deposits forming around the higher-temperature vents and still others argued their importance to national interests—whatever it took to get them into this new and exciting game.
The initial phase of follow-up studies began in full force in 1980 with an expedition to the Galapagos Rift by the National Oceanic and Atmospheric Administration (NOAA) scientists under the leadership of Alex Malahoff. This expedition resulted in the discovery of major polymetallic sulfide deposits and increased interest in their commercial potential.
In May and June of that same year, Jean Francheteau of CNEXO, France, invited me to participate in an explorer's dream: a three-month-long journey down the East Pacific Rise aboard their premiere research ship the N/O Charcot. Taking advantage of the latest American technology in bottom mapping, the French had purchased the first unclassified multi-narrow beam sonar system called a shipboard multi-transducer swath echo sounding system (SEABEAM) and mounted it on the hull of the Charcot. For the first time, the scientific community could survey potential dive sites along the Mid-Ocean Ridge quickly and in great detail without having to rely upon the Navy as we had done in the FAMOUS area, Cayman Trough, and Galapagos Rift.
The timing could not have been better. By now, it was clear to Jean and me that there were a variety of factors controlling the distribution of hydrothermal vents along the axis of the Mid-Ocean Ridge. Clearly, they were situated in the youngest volcanic terrain characterized by the central axis.
The magma chambers feeding the most recent flows were also the obvious heat source for the active vents. The faster the spreading rate, the more likely were vents to be found, shifting the focus of our studies from the slow-spreading Mid-Atlantic Ridge to the faster-spreading East Pacific Rise.
But our studies along the axis of the Galapagos Rift in 1977 and 1979 and our studies at the East Pacific Rise at 21°N in 1978 and 1979 revealed a significant along-strike variation. This was even true for the axis of the Mid-Atlantic Ridge in the FAMOUS where venting had not been found. The ridge is divided into a continuous series of spreading segments bound at each end by transform faults that offset the ridge to either side. As the intersection between the axis and transform fault is approached, the depth of the axis begins to increase. Since the topography of the ridge is the result of thermal expansion, the higher the elevation of the axis, we reasoned, the more likely were we to find hydrothermal activity.
With the SEABEAM system now installed on the N/O Charcot, Jean and I could run along a major length of the East Pacific Rise testing our model in our search for new sites of hydrothermal venting. From May until July 1980, the Charcot slowly zigzagged down the axis of the East Pacific Rise at 22°N to its fastest-spreading segment at 22°S near Easter Island. From these survey lines, we could clearly see individual spreading segments along the strike of axis, each having topographic highs where we felt active venting might be found.
Our first chance to test this model came in April 1981 with a cruise aboard the R/V Melville to the East Pacific Rise at 20°S. Using the Charcot's SEABEAM maps to guide us, we conducted a series of Angus camera runs down the axis of a fast-spreading segment of the ridge near its topographic high and quickly found active hydrothermal vents.
In January 1982, we had another chance to test this model when Jean brought the submersible Cyana aboard the N/O Le Suroit to dive at 13°N on the East Pacific Rise, a site surveyed in 1980 by the Charcot . Once more, the model proved to be an excellent prediction for finding active hydrothermal vents. We even dove in the Cyana where we did not expect to find vents near the axis-transform intersection and didn't.
By now, we were not the only team searching for new vent settings on the Mid-Ocean Ridge. Peter Lonsdale from Scripps, who had played a major role in the discovery of the hydrothermal vents in the Galapagos Rift, was using his considerable skills to search for vent sites in the Gulf of California. The focus of his research was a series of small spreading segments in Guaymas Basin. His efforts proved equally successful in January 1982, when a series of dives by Alvin located and investigated a number of active vents. What made these vents unique was their occurrence in an area of thick sediments.
At the northern end of the Gulf of California is the Colorado River delta. For millions of years this river has deposited a tremendous volume of organic-rich sediments into the gulf, including Guaymas Basin. As a result, the active spreading axis underlying the gulf is buried under a thick accumulation of mud. Hydrothermal fluids that flow out of fissures cutting across the young central volcanic terrain must then rise hundreds of meters through this sediment cover before exiting into the basin's bottom waters. During this final vertical journey, these superheated fluids interact with the overlying organic sediments, greatly altering their chemistry. Oil seeps of thermogenic petroleum hydrocarbons were commonly associated with active vent sites and the soft sediment surface was covered by extensive bright yellow and white bacterial mats.
From 1981 on, the investigation of hydrothermal circulation in the ocean's crust intensified and spread throughout the word. A team headed by Peter Rona of NOAA located hydrothermal vents in the Mid-Atlantic Ridge. Both French and American researchers found additional vents along the East Pacific Rise at 10, 11, and 13°N. From 1982, active hydrothermal vents were discovered on the East Pacific Rise at 13°N followed in 1984 by the discovery of similar vents sites on the Juan de Fuca Ridge and Discover) Ridge off the coast of Washington and British Columbia.
As more active hydrothermal sites were discovered on the East Pacific Rise, the search broadened to include other geologic settings. Dives by Alvin in the Marianas Back-arc basin successfully located active vents. These discoveries were followed by expeditions to the Mid-Atlantic Ridge, which located active vent sites at 26 and 23°N. More recently, hydrothermal vents have been found t,-, the north on the Mid-Atlantic Ridge at 37°17.5'N and 37°50'N. In these latter instances, the vent sites are near the Azores "hotspot" and associated with large lava lakes.
Once high-temperature vents were discovered along the East Pacific Rise at 21°N in 1979, additional important vent animals were added to the list. Perhaps the most impressive was a worm dubbed the "Pompeii Worm" for its ability to live in close proximity to the black smokers, where the exiting vent temperature can exceed 350°C. These worms (Alvinella pompejana) live in tiny tubes that are constantly being covered by fine-grain minerals precipitating out of the vent waters once the hot fluids come into contact with cold ambient seawater.
The dominant organisms associated with the hydrothermal vent communities of the Eastern Pacific (i. e., Galapagos Rift, East Pacific Rise, Guaymas Basin, and Juan de Fuca/Discovery Ridges) include the long, red-tipped vestimentiferan tube worms, large white bivalve clams, and thick accumulations of mussels. Variation in the vent faunal assemblages is thought to be related to differences in vent flow and water chemistry, with higher concentrations c [ biomass associated with lower-temperature vents (i.e., 5-200°C) compared to the higher temperature vents (i.e., 200-360°C).
The two giant-sized mollusks mentioned earlier are the clam-like Calyptogena magnifica and the mussel Bathy
modiolus thermophilus. The clams live on the outer perimeter of the vent site, commonly found in small crevices where low-temperature vent fluids are coming out of the fractured volcanic terrain. They have a long foot that aids them in moving as well as feeding, primarily for the uptake of vent fluids while their gills absorb oxygen and inorganic carbon from the circulating bottom waters.
The mussels, on the other hand, are commonly found in high-temperature settings near the vent opening and apparently ingest bacteria directly through filter feeding. Such direct ingestion of food is thought to be secondary to their primary source of nutrition from symbiotic bacteria living within their bodies. Other mollusks include limpet-like gastropods and whelks.
The most spectacular organisms associated with many hydrothermal vents are the large white, red-tipped vestimentiferan tube worms, Riftia pachyptila. Living in a highly precarious setting of varying levels of oxygen and temperature, this organism is truly unique. It lacks a mouth, gut, and digestive system and relies upon the symbiotic bacteria that make up half its body weight to feed it. Since these tube worms live where reduced vent fluids mix with the oxygenated bottom water, they need to withstand prolonged periods of time when anoxic conditions prevail. As a result, their blood includes human-like hemoglobin, which stores oxygen within their body.
Another fascinating worm living under an even harsher vent setting is the Pompeii Worm, Alvinella pompejana. These live in a mass of honeycomb-like tubes near high-temperature vents that they freely move in and out of. Their tubes have even been seen attached to sulfide chimney walls of 350°C black smokers, although they must live in the highly mixed waters having a lower temperature.
Scavenging and carnivorous brachyuran crabs are also associated with the vent communities, as well as numerous other organisms including anemones, siphonophores, fish, shrimp, and so forth, too numerous to describe in any detail here.
In 1984, an entirely different geologic setting was found in which similar organisms are living. Cold water seeps on the West Florida Escarpment in the Gulf of Mexico were discovered that support sulfide-oxidizing benthic communities. Groundwater flowing through porous limestone releases sulfide and methane-enriched water that leads to the growth of chemosynthetic bacterial mats and symbiotically supported communities of large mussels and vestimentiferan worms. These communities also include galatheid crabs, gastropods, sea anemones, serpulid worms, and other organisms typical of warm water vent settings.
Further to the west in the Gulf of Mexico, cold water seeps of hydrocarbons including methane were found to support similar benthic communities. More recently, hydrocarbon seeps off the west coast of California, in the North Sea, and the Sea of Okhotsh have been found to support a similar assemblage of organisms. Even the oily bones of a decomposing whale off California provide a home for this unique biological ecosystem. The investigation of seamounts was also expanded to include the investigation of craters, calderas, and pyroclastic deposits on seamounts in the Pacific.
Clearly in years to come, chemosynthetic animal communities will be found throughout the world's oceans and lakes wherever the conditions arise to spawn this unique symbiotic relationship. As this paper is being written there are those who are turning their thoughts to the volcanic terrains of Mars or the ice-capped ocean of Europa. Such thoughts include the continuing debate dealing with the very origin of life on our planet.
ALVIN BECOMES A ROUTINE TOOL IN MARINE RESEARCH
Following the excitement of the later 1970s and early 1980s, Alvin's annual diving program pushed north from the East Pacific Rise off Mexico to include regular visits to the Juan de Fuca, an isolated segment of the Mid-Ocean Ridge, connected millions of years ago to the East Pacific Rise. Dives in the Juan de Fuca and Gorda Ridges off the coasts of Oregon and Washington in 1984 resulted in the discovery of hydrothermal vents and high-temperature black smokers.
With increased funding from the National Science Foundation, the engineers supporting the Alvin program now were able to "harden" its capability and make major improvements in its propulsion, electrical, and instrumentation systems. Returning to the Mid-Atlantic Ridge after its lengthy overhaul in 1986, Alvin was able to investigate newly discovered hydrothermal vents and a unique benthic animal community dominated by shrimp.
In 1987, Alvin crossed the Pacific Ocean for the first time in its history, stopping in the Hawaiian Islands. There scientists investigated Loihi Seamount along the volcanic ridge extending southeast from the big island of Hawaii before continuing west to the Mariana Islands. A team of scientists had discovered hydrothermal vents in the back-arc basin west of the Mariana Islands, and Alvin was used to document and sample their chemistry and unique biology. Following what would be its only expedition to the western Pacific, Alvin and its support ship Atlantis II returned to San Diego for maintenance and repairs.
For the next 10 years, Alvin's diving schedule became fairly routine, journeying back and forth along the West, East, and southern coasts of the United States with frequent visits to the Juan de Fuca Ridge and Oregon coast, the California continental borderland, the East Pacific Rise, Guaymas Basin, Galapagos Rift, Mid-Atlantic Ridge, Bermuda, and the East Coast.
The investigation of hydrothermal vents including coldwater seeps continued to dominate Alvin's use, but other programs emerged as well. These included the continued investigation of seamounts and the investigation and instru
mentation of the Ocean Drilling Program drill holes. During this same period of time, many improvements were made to Alvin's various sampling and imaging systems and its operating depth was increased to 4,500 m.
After years of development and use, the unmanned remotely operated vehicle program at Woods Hole was finally integrated into the Alvin operational schedule with the arrival of its new support ship Atlantis. It is now up to the deep submergence user community to determine the long-term viability of manned submersibles such as Alvin.
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