In Search of Heat: A Brief History of the Search for Hydrothermal Vents on the Deep Seafloor
Dr. Kathleen Crane, Ph.D., Program Manager, NOAA Arctic Research Office
Professor, Hunter College, CUNY
Paula Keener-Chavis, National Education Coordinator
NOAA Office of Ocean Exploration
In the early 1960s, marine geologists believed that the amount of heat emanating from the sea floor would be highest in areas where hot magma erupted under the ocean. This should be at the mid-ocean ridges where sea floor spreading occurred. But as scientists pushed their newly-designed heat flow probes into the sediments of the ocean floor near mid-ocean ridges, they found that the heat flow was much lower than they had expected. The heat flow probes were only designed to measure conductionheat transferwithout the movement of material. When they took measurements closer to the mid-ocean ridges, the conductive heat flow was curiously much lower than expected, which baffled the scientific community. At first, they thought the heat in these areas was missing until they realized that the heat might be escaping via the eruption of hot water springs. When heat flows with moving material like hot water or magma, the process is called convection. The original heat flow probes were not designed to measure convection.
By the early 1970s, scientists suspected that the heat might be escaping from mid-ocean ridges through hydrothermal venting. After all, the sea floor was covered with volcanoes and a lot of water from the oceans above (heat + water should equal hot water). But no one had ever seen a deep-sea hot spring and no one had conclusive evidence that these vents actually existed. In fact, because of the great pressures on the sea floor, some speculated that hot springs could not form because water could not boil. Yet the believers persisted, and from 1972 to 1974, the evidence mounted. Scientists noted the elevated water temperatures at the bottom of the deep, cold ocean, unusual 75-foot high mounds on the sea floor, and mini-earthquakes occurring at an unusual frequency of 80 per hour miles beneath the surface of the seafloor. Scientists were now on to clues that might help solve the mystery of why mid-ocean ridges were not as hot as they should be. The area offering up the most clues was the Galapagos Spreading Center.
The Search Continues
During the next several years, there was a flurry of activity similar to the effort that it takes to prepare for and successfully carry out a NASA mission. In 1974, the United States and France, five research vessels, three deep-water submersibles, and hundreds of scientists and ships' crew went in search of what had to be the answer to the missing heat along the Mid-Atlantic Ridge. It was here that scientists made their first in-situ observations from an occupied submersible of a mid-ocean ridge. Indeed, humans and their technology made history as they descended more than 5,000 feet into deep rift valleys on the ocean floor. But there were no signs of hydrothermal vents during what almost proved to be a disastrous voyage to the bottom of the sea. The deep sea submersible, Alvin, had become wedged in a crack. Only after rocking the submersible in every direction possible did the rocks break free and allow Alvin and its crew to escape the grasp of the mid-ocean ridge.
Two more years passed and additional clues were coming in from scientists about activity at the Galapagos Spreading Center. Scientists from Scripps Institution of Oceanography using the Deep-Tow, a side-looking sonar outfitted with numerous sampling devices, detected a narrow temperature spike, rising 125 feet above the sea floor. Underwater cameras had also photographed white and yellow rocks and long, empty clamshells. These marked a site named Clambake. To guide future expeditions back to the site, Scripps scientists lowered a long-life transponder navigation beacon down onto Clambake. One year later, geologists, geochemists and geophysicists mostly from Oregon State University, Woods Hole Oceanographic Institution (WHOI), and Scripps Institution of Oceanography revisited this site to continue their search. They used the deep-sea research submersible Alvin. No biologists were on board and only rudimentary biological sampling equipment.
On Feb. 17, 1977, WHOI's R/V Knorr, the R/V Lulu and the submersible Alvin, reached the Galapagos Spreading Center. The site was the furthest the Lulu had ever been from its homeport.
During the Alvin dive, the divers were guided to the sea floor target by the trail of white clamshells strewn across the dark volcanic background. Suddenly, they discovered that coming out of small cracks cutting across the lava terrain was warm shimmering water that quickly turned cloudy blue as manganese and other chemicals in solution began to precipitate out of the warm water and were deposited on the lava surface, where they formed a brown stain. (Robert Ballard, Oceanus Magazine, 1977).
Humans visited a deep-sea hydrothermal vent for the first time on that day, and the world of oceanography has not been the same since. Scientists would learn that the cycling of hot water through the ocean crust and back into the oceans was the process that enriched the sea with salt. The heat rising from below was found to be so vast that now it is believed that undersea hot springs may be the driving force for many previously unknown deep sea currents.
Even more surprising than the discovery of hot water was the rich biological communities associated with the vent site. For the first time, scientists understood that the deep sea was not devoid of life. Live clams over one foot long and orange animals that had never been seen before filled the view ports of the tiny submersible. Newly discovered vent sites were given the names Dandelion Patch, Clambake 2, and Oyster Bed. Eventually, they discovered the Garden of Eden, a lush community of foot-high tube worms with red tops swaying in the water.
Literally every organism that came up was something that was unknown to science up until that time. It made it terribly exciting. Anything that came [up] on that basket was a new discovery, said Richard Lutz of Rutgers University. We all started jumping up and down. We were dancing off the walls. It was chaos. It was so completely new and unexpected that everyone was fighting to dive [in Alvin]. There was so much to learn. It was a discovery cruise. It was like Columbus, commented John Edmond of the Massachusetts Institute of Technology.
After years of searching, what was discovered on the sea floor drastically changed our fundamental understanding of the evolution of life on the ocean planet. Twenty-five years later, as scientists from NOAA, WHOI, and other universities revisit the Galapagos Spreading Center, one can only wonder about the discoveries about to reveal themselves as we probe more deeply into our underwater world.
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