ASU Research E-Magazine: Making More Ocean Floor

One type of crab that lives in the Pacific Ocean looks like a tarantula, swims like a squid, and can survive the scalding supersonic blasts of hot water steaming from a volcanic vent on the sea floor. Tracy Gregg saw the crab during one of her two dives on the Alvin deep-sea submarine in 1994. She watched the crab swim into the blast of an undersea volcanic vent that scientists call a black smoker. The crab’s encounter with water heated to about 570 degrees Fahrenheit left it only momentarily stunned.

"They’re just phenomenal creatures," says Gregg, who completed her doctoral degree in geology at Arizona State University in June. Gregg spent much of the past year working in the lava-flow simulation laboratory of geology Professor Jonathan Fink.

Gregg currently is continuing her deep-sea research at the Woods Hole Oceanographic Institute in Massachusetts. The National Science Foundation awarded her one of two 1995 RIDGE postdoctoral fellowships.

The fellowship enables her to devote the next two years conducting midocean ridge research in the Atlantic and Pacific with Woods Hole research scientist Daniel Fornari.

"Our understanding of volcanic eruptions on the sea floor is limited because of the remote setting and deep depths, and our reliance on various acoustic and imaging techniques to determine volcanic evolution and history," Fornari says.

"The modeling that Tracy has done in Jon Fink’s lab at ASU holds great promise for increasing our ability to comprehend why sea-floor lava flows attain the shapes that they do and, to a first order, how fast they erupt on the ocean floor."

Gregg’s research has applications both in predicting the behavior of lava flows on Earth and in assessing the make-up of lava flows on other planets.

During her Alvin dives, Gregg saw lava flows as well as crabs along the East Pacific Rise, a volcanically active area off the coast of Mexico.

"As a geologist you really have to use the biology," she explains. If Gregg sees a mussel while cruising the sea floor, it’s a clue that she may find a volcanic vent nearby.

"I don’t think there’s any other place on Earth where it’s quite so clear how much the biology and the geology tell the same story. It’s all intertwined. You never find one without the other," Gregg says.

Life colonizes around the chemical-rich warm water provided by the lava flows. When lava erupts on the sea floor, it heats up the surrounding water. Deposits of sulfur and other minerals also build up around vents, just like they do around the geysers at Yellowstone National Park. The difference is, sulfur forms the base of the food chain on the sea floor.

"Everything either eats the sulfur, or eats something that eats the sulfur," Gregg says.

During her on-location work, Gregg almost literally got a taste of the sulfur while spending four hours helping to sort a large sample of mussels for another researcher. "The sulfur smell was so strong, it just made your eyes water and your mouth burn."

Smelly or not, biologists still puzzle over the sea floor’s sulfur-eating bacteria. At first they thought the bacteria were primitive survivors from early in Earth’s history.

But the bacteria are so complex, biologists now wonder if they might not be some of the planet’s most recently evolved life forms. According to one theory, the organisms come from beneath the sea floor.

"Anytime a black smoker pops up, they (the bacteria) don’t have to come from somewhere else," Fink says. "They’re already there. Beneath the surface of the Earth, covering the entire sphere, may be this huge population of these little things. They’re actually in rocks."

Some of the larger life forms found in the deep ocean are no less exotic, including the dumbo octopus, so-called because of its huge, earlike fins. "No one knows what the fins are for or how the octopus uses them," Gregg says.

Giant tube worms grow to lengths of several feet and look like they belong on another planet. Much smaller worms the color of red spandex live inside mussels. "They look like they were stamped out of a rubber mold. They don’t look real," Gregg says.

Crabs are among the most common creatures found along the East Pacific Rise. Most creatures that live on the sea floor are so adapted to life there that they cannot survive a trip to the surface almost two miles above.

The pressure change is so great that these creatures literally explode. It happens to sea-floor bacteria and even rocks, if gas is trapped inside them. Not so the crabs.

"You can bring the crabs up to the surface. They scuttle around on deck. You can bring them back down and they just scoot away. They’re not affected at all," Gregg says.

The most common animals on the sea floor, however, are the shrimplike amphipods. They, like the crabs, apparently can swim through the black smokers unharmed. "They look very delicate. They actually look like the sea monkeys that used to be advertised for sale in comic books," she adds.

Although Gregg and Fink find life on the sea floor fascinating, geology is the real subject of their research. Gregg’s dives on the Alvin have enabled her to better understand the results of her 225 laboratory experiments simulating marine lava flows.

A third cruise aboard a surface vessel off the coast of Oregon also helped. The ship filmed the ocean floor by towing a video camera at the end of a 13,000-foot wire. Gregg and Fink published their experimental results in the January 1995 issue of the journal Geology.

Their experiments are the first to quantify the flow rates of sea-floor lavas, according to Robert Embley, a senior researcher with the National Oceanic and Atmospheric Administration in Newport, Ore. Their findings help geologists understand how new ocean floor is created along the Earth’s 37,200 miles of midoceanic ridge.

"Lava erupts somewhere along the midocean ridge many times per year, but the timing and volume of these eruptions are rarely documented," Embley says.

"The Gregg/Fink study represents a pioneering effort to compare rates of eruption along the midocean ridge, which is a fundamental step to understanding the variation of the rate of heat and chemical release into the ocean."—Steve Koppes