When scientists on a research cruise in the Atlantic Ocean first stumbled across an underwater landscape of giant white towers and feathery spires, they only had time for a quick look around.

"We got just the teeniest glimpse," said University of Washington oceanographer Deborah Kelley, who led that voyage in 2000. Excited by the discovery of what looked like a new type of hydrothermal vent field, she organized a monthlong return trip three years later to the "Lost City," named for the mythical world of Atlantis.

In today's issue of the journal Science, Kelley and her colleagues report the results from that expedition, including the surprising find that the geysers are populated by more than 65 types of tiny creatures, including transparent worms, water fleas and mats of bacteria that waft in the currents like kelp. The animals and microbes thrive in scalding hot fluids nearly as caustic as Drano. Many seem to subsist on a "diet" of natural gas and hydrogen.

"It really changes our ideas about where life can live on this planet," Kelley said. "And it really drives home that there's still a huge amount yet to be discovered in the oceans."

The scientists believe the undersea vents could mimic conditions on the primordial earth when life first formed, and may provide some of the best insights into that process.

The hope is to find living fossils that "tell us something about what the earliest organisms were like," said UW microbiologist John Baross, who is trying to grow some of the microbes collected on the voyage in his Seattle laboratory.

Though no one has ever seen anything like the Lost City before, there are almost certainly many sites like it, Kelley said.

"There are probably much larger areas of the sea floor that host hydrothermal vent systems and all of these new types of organisms — and to date we know almost nothing about them," she said.

Scientists have been studying hot springs on the sea floor since the late 1970s, when they first discovered an astounding array of giant tube worms, clams and swarms of shrimp living in and around volcanic vents called "black smokers." Some of the best-known "smokers" lie in the Pacific off the Washington coast.

But the Lost City is a very different type of environment, Kelley and her team found.

All of the hydrothermal fields discovered previously are along rifts on the ocean floor where molten rock flows to the surface. That lava heats the fluids in black smokers to a searing 700 degrees and creates a brew rich in metals, acids and carbon dioxide, which nourishes the microorganisms that form the basis of a unique food chain.

In contrast, the Lost City is perched on a plateau on the Atlantis massif — an underwater mountain the size of Mount Rainier, located in the mid-Atlantic miles from the nearest volcanic rift.

The heat that drives the system comes from a chemical reaction between sea water and ancient oceanic bedrock. Temperatures are a milder 100 to 200 degrees. When the hot water bubbles up and hits the icy sea, dissolved carbonate minerals precipitate out, forming white and gray towers that rise like giant limestone stalagmites.

Unlike at black smokers, the chemistry at Lost City is dominated by methane, or natural gas, and hydrogen. The dominant type of microorganisms belong to a group called Archaea, bacterialike bugs, some of which are known to metabolize methane, Baross said.

The monolithic chimneys at the Lost City are also taller than most black smokers. One 18-story behemoth the scientists nicknamed Poseidon would tower above the Interstate 5 bridge over Portage Bay, Kelley said.

Another researcher whimsically described the site as "a conglomeration of colossal beehives from outer space." Director James Cameron was so taken with the eerie scene he featured it in his IMAX film, "Aliens of the Deep."

"If it was on land, it would probably be a national park," said David Butterfield, a geochemist from the University of Washington who participated in the 2003 voyage along with researchers from Woods Hole Oceanographic Institute, the Massachusetts Institute of Technology and several other universities.

With funding from the National Science Foundation, the scientists used the deep-sea submersible Alvin for their explorations. They made 19 dives, each lasting about eight hours, Kelley said. That includes the 25 minutes it took each morning just to submerge to the site, about half a mile below the surface.

Once they arrived, the scientists maneuvered around the spires with only the sub's headlights to show the way.

"You're essentially flying around in this deep blackness, moving up and down these very tall structures," Butterfield said. "If the currents aren't too bad and you can actually get the submarine to sit still long enough, you hover there and put out a hose to collect water samples."

The team also used Alvin's robotic arms to break off sections of the columns and scoop up some living organisms, including one large crab.

During the first visit to the site five years ago, it looked devoid of animal life, Kelley said.

But during the return trip, when the scientists ran a vacuum attachment over the columns, they discovered a wide range of snails, worms and tiny crustaceans in the nooks and crannies.

While living creatures are not as plentiful as at the black smokers, the diversity of species is comparable.

After devoting their daylight hours to the Alvin dives, at night the research team launched a remotely operated vessel that cruised through the depths, mapping the site with radar.

Robotic vessels will be the centerpiece of a third expedition this summer. The probes will film the hydrothermal field and its inhabitants and collect samples. Data will be transmitted instantaneously to Kelley in Seattle, and to aquariums, museums and classrooms across the country.

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com

Information

"Lost City" expedition: www.lostcity.washington.edu

View a video: uwnews.org/