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Deep-sea exploration to the 'Lost City'

Actively venting carbonate pinnacle on the top of the 60 meter-tall structure Poseidon. Small, delicate flanges host dense arrays of filamentous bacteria that get nutrients from fluids from methane- and hydrogen-rich solutions that bathe these deposits. The arm of the submersible Alvin is shown in the right portion of the image. [Image courtesy of University of Washington]
Click here for a full image.

Lost City isn't actually a city. It's an area at the bottom of the Atlantic Ocean where giant towers made of glistening white minerals rise up to 200 feet off the seafloor.

When scientists discovered the towers by accident during an ocean research trip back in 2000, they were astonished.

No one had ever seen anything like Lost City before.

The top of a 30 m tall carbonate pinnacle on the east side of the field. Most chimneys display multiple pinnacles. The porous structure of these deposits and “nooks and crannies” on the outside surfaces provide wonderful habitats for microorganisms and small animals to live. [Image courtesy of University of Washington]
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The full name of the region is the Lost City Hydrothermal Field. That's because fluids seeping through the seafloor, called "hydrothermal fluids," play an important role in the growth of these towers.

In the 4 March issue of the journal Science, the research team now describes what it discovered when it returned to the Lost City for a closer look.

The trip lasted 32 days and took the team to a spot in the Atlantic ocean that's about halfway between North America and Europe and roughly at the same latitude as Bermuda.

Parasitic flange deposit growing from the trunk of a 30 meter-tall, actively venting edifice. Hydrothermal fluids pool underneath the flange and flow out from under the lip of the deposit, adding to its length. The flange is about 1 meter in length. The two red dots are lasers from the submersible Alvin and are 10 centimeters across. [Image courtesy of University of Washington]
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The ship carried two smaller vehicles that the researchers could use to study Lost City. One was the submersible named Alvin, which can take three people down to the seafloor. The other was a remotely operated vehicle called ABE that travels underwater by itself.

According to team-leader Deborah Kelley of the University of Washington, ABE traveled back and forth along the seafloor "like a lawn mower" to map out the Lost City region.

The researchers collected rocks and fluids from Lost City and brought them back up to the laboratories on their ships to study the geology, chemistry and biology of the area.

Same image as that shown in Image 1, but from a bit farther back. The darker structure immediately behind this pinnacle is less active, showing a typical dark grey color. [Image courtesy of University of Washington]
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There are other types of hydrothermal systems on the seafloor, where scorching-hot fluids leak through volcanic rock. The fluids are filled with black, sulfur-bearing minerals and the chimneys are black too. Lost City is dramatically different from these systems.

At Lost City, the fluids seeping from the seafloor contain high levels of methane and hydrogen. When the fluids mix with the seawater, solid white crystals of a mineral called calcium carbonate form, growing the towers.

The towers of Lost City sit upon a mountain that's made of much older rock than what's found in the "black smoker" systems. This type of mountain is fairly common beneath many of the world's oceans, so Kelley and her colleagues now believe that more Lost Cities are out there waiting to be found.

Kelley's team discovered a group of single-celled organisms called archea living in the inner walls of the towers. Outside the towers they found a wide variety of larger life forms, such as worms and clam-like creatures.

Kelley marveled at how life has adapted to the harsh conditions at Lost City. Although the hydrothermal fluids aren't terribly hot, they have an extreme chemistry that would be unfriendly to most life forms.

"Even though it's a very extreme environment, it's one of the most peaceful places I've seen," she said. "It's very beautiful in its own way."


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