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50 Years of Ocean Discovery: National Science Foundation 1950—2000
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.