Environment

British scientists say Caribbean yields deepest ever 'black smoker' vents

Wednesday, January 18, 2012    

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LONDON, England (CMC) — British scientists say a group of volcanic vents on the Caribbean seafloor are the deepest discovered to date, adding that another field of vents on a nearby submerged mountain suggests that so-called "black smoker hydrothermal vents" may be much more common than previously believed.

The scientists said the vents — about three miles deep in a rift in the Cayman Trough, south of the Cayman Islands — may be hotter than 450 °C and are shooting a jet of mineral-laden water more than a kilometre into the ocean above.

Despite extreme conditions, the vents are teeming with a new species of shrimp that has a light-sensing organ on its back, said the scientists, reporting the results this week of the 2010 expedition in the journal, Nature Communications.

The deep-sea research was led by marine geochemist Doug Connelly at the National Oceanography Centre in Southampton and marine biologist Jon Copley of the University of Southampton.

The researchers said they also found black smoker vents on the upper slopes of an undersea mountain called Mount Dent.

Mount Dent rises nearly three kilometres above the seafloor of the Cayman Trough, but its peak is still more than three kilometres beneath the waves.

The scientists said the mountain formed when a vast slab of rock was twisted up out of the ocean floor by the forces that pull the plates of the Earth's crust apart.

"Finding black smoker vents on Mount Dent was a complete surprise. Hot and acidic vents have never been seen in an area like this before, and usually we don't even look for vents in places like this," said Connelly.

"Because undersea mountains like Mount Dent may be quite common in the oceans, the discovery suggests that deep-sea vents might be more widespread around the world than previously thought," he added.

The team named the Beebe Vent Field after the first scientist to venture into the deep ocean. They are gushing hot fluids that are unusually rich in copper, and shoot a jet of mineral-laden water four times higher into the ocean above than other deep-sea vents.

Although the scientists were not able to measure the temperature of the vents directly, these two features indicate that the world's deepest known vents may be hotter than 450 °Celsius, the researchers said.

"These vents may be one of the few places on the planet where we can study reactions between rocks and 'supercritical' fluids at extreme temperatures and pressures," Connelly said.

He said the team found a new species of pale shrimp congregating in hordes around the 18-feet tall mineral spires of the vents.

Lacking normal eyes, the shrimp instead have a light-sensing organ on their backs, which may help them to navigate in the faint glow of deep-sea vents, Connelly.

He said the researchers named the shrimp Rimicaris hybisae, after the deep-sea vehicle that they used to collect them.

"Studying the creatures at these vents, and comparing them with species at other vents around the world, will help us to understand how animals disperse and evolve in the deep ocean," Copley said.

The vents on Mount Dent, which the team has named the Von Damm Vent Field to commemorate the life of geochemist Karen Von Damm, are also thronged with the new species of shrimp, along with snake-like fish, and previously unseen species of snail and a flea-like crustacean called an amphipod.

"One of the big mysteries of deep-sea vents is how animals are able to disperse from vent field to vent field, crossing the apparently large distances between them. But maybe there are more 'stepping stones' like these out there than we realised," Copley said.

The United Kingdom expedition that revealed the vents followed a United States expedition in November 2009, which detected the plumes of water from deep-sea vents in the Cayman Trough.

A second US expedition is currently using a deep-diving remotely operated vehicle to investigate the vents further.

The UK team also plans to return to the Cayman Trough in 2013 with Isis, the National Oceanography Centre's deep-diving remotely operated vehicle, which can work at depths of up to six kilometres.

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