Image: Courtesy of the National Science Foundation

Scientists on a research cruise aboard the Atlantis have stumbled upon a spectacular discovery in the Atlantic Ocean: a system of hydrothermal vents so vast they have named it the Lost City. Indeed, this vent field is the largest yet known. Moreover, the vents appear to have formed under unique circumstances that should shed light on ancient hydrothermal systems, as well as on the evolution of the surrounding area.

The team didn't set out to look for vent systems. Rather they have been studying an enormous mountain known as the Atlantis Massif, which forms part of the Atlantic Ridge, one of the world's biggest undersea mountain ranges. But explorations of the mountain revealed the vents. "These structures, which tower 180 feet above the seafloor, are the largest hydrothermal chimneys of their kind ever observed," says geologist Deborah Kelley of the University of Washington. The deposits consist of spires that can reach 30 feet in width at their tops, and delicate flanges adorn their sides (above). Even more surprising than the enormous size of the vents, however, is their composition: carbonate minerals and silica, as opposed to the iron and sulfur-based minerals that make up most other mid-ocean ridge hot spring deposits. And unlike other such hydrothermal environments, the Lost City does not appear to house clams, shrimps, mussels, tube worms and other macrofauna. The warm fluids trapped beneath the flanges, however, do support microbial communities.

The team returns from the expedition this weekend, after which analyses of the rocks, fluids and biological samples they've collected can begin--studies that should reveal more about Atlantis Massif, and the Lost City on it. "If this vent field was on land," says structural geologist Jeff Karson of the Woods Hole Oceanographic Institution, "it would be a national park."

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