By Carolyn Fry

The team on board the research vessel RRS Charles Darwin made the find when they detected a huge, dark plume of water, 600 metres thick and over 30 kilometres wide, rising hundreds of metres above a lava-strewn valley on the Carlsberg ocean ridge.

"Black smokers", often teeming with exotic lifeforms, are known to exist in the Pacific and Atlantic Oceans but their discovery in the Indian Ocean is very recent.

"The source of the plume is comparable to a suite of power stations churning out vast amounts of heat and smoky water," said Dr Bramley Murton, the scientist leading the research cruise.

HYDROTHERMAL VENTS Existence first established 1977 Associated with volcanic activity Water drawn through seafloor cracks is superheated and ejected through vent openings Hot fluid carries dissolved metals and other chemicals from beneath ocean floor Evolution of extraordinary organisms around vents Chemosynthesis process sustains ecosystems - not photosynthesis

Underwater volcanoes and the associated hydrothermal activity occur in areas of sea-floor spreading.

Where the Earth's crust moves apart in the deep ocean, molten material rises to fill the gaps.

Water percolates down below the seabed and is superheated before gushing out from hot springs or vents at about 300 to 400 Celsius.

The smoky plume comes from iron-rich particles that precipitate when hot mineral-laden fluids mix with cold deep-ocean water.

"If you think of a factory chimney pouring out smoke on a still day, the smoke goes vertically upwards but as it entrains air, eventually stops rising and starts to spread out," explained Dr Lindsay Parson, project leader of the mid-ocean ridge research group at Southampton Oceanography Centre (SOC), UK.

"That's exactly what these smokers do under water."

Tubeworms are known in the Pacific

The communities of animals found at hydrothermal events are specially adapted to thrive in the turbulent, toxic environment.

Most depend on bacteria that use energy from chemicals in the water to make organic matter.

The next move for the research team is to organise an expedition to investigate the marine life.

The site may be a suitable test ground for SOC's new ultra-deep remotely operated vehicle, Isis, which can explore ocean environments down to 6,500 metres.

"The Indian Ocean is the largest ocean that's left where we're still not sure what critters live there," explained Dr Parson.

Isis can go down to over 6,000 metres

"Lifeforms that live in the Pacific Ocean on these sorts of vents are dominated by tubeworms.

"We don't know of tubeworm communities in the Atlantic but we know there are fantastic numbers of specially adapted shrimps.

"This discovery is the link to find out whether the Indian Ocean communities are more like the Pacific or Atlantic, or whether they're some form of hybrid. It's like the Holy Grail to biologists worldwide."

US and Japanese researchers have previously explored vent activity elsewhere in the Indian Ocean.