1976 - Homing In

More clues from the Galápagos

The 1972 Southtow expedition to the Galápagos Rift had uncovered some intriguing evidence for hydrothermal vents, so Scripps scientists, led by Peter Lonsdale and Ray Weiss, returned for another look in May of 1976 aboard R/V Melville.

For this expedition, called Pleiades, the Deep-Tow “fish” was specially outfitted with new equipment attached to its belly. These included a new sensor to measure water temperature and a rack of bottles to sample deep-sea waters.

The sensor detected a narrow zone of water with temperatures about 0.2°C higher than the surrounding seawater. The spike rose up to 125 feet above the seafloor. Was it a plume of buoyant, venting hydrothermal fluids? Chemical analyses of the fluids collected in the special sampling bottles later indicated that a vent might well be there. The new evidence was exciting, but it was still circumstantial and did not prove the existence of hydrothermal vents.

Frosted fractures and a pile of clamshells

Deep-Tow’s cameras also captured photos near a gaping seafloor fissure below the place where the temperature spike was measured. The photos showed rocks that seemed to be “frosted” with white and bright yellow deposits. At the time, it was difficult to conclude for sure that these were minerals precipitated from hydrothermal vents. They might have been meaningless white spots caused by chemical spills when the old black-and-white film was processed!

Deep-Tow also took photos of a pile of big, long, empty, white clamshells strewn on the seafloor (along with one beer can!) This, too, was curious. But it could have been garbage thrown overboard after a party aboard a ship. The scientists called the site “Clambake,” and marked the spot with transponders. Transponders transmit sound signals that scientists and deep-sea vehicles can home in on to determine their location. The transponders left behind by the Pleiades expedition would allow scientists on subsequent expeditions to find the site again.


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