BioEd Online

Undersea 'hotspots', which spew super-hot, mineral-rich fluids out of the sea floor and play host to a variety of weird marine life, just got weirder: scientists have found one blowing out blue smoke.

Hydrothermal vents commonly spit out clear bubbles, or black, grey or white smoke. But a 'blue smoker' has never been reported before, says Ken Takai, a geomicrobiologist at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in Yokosuka, which unveils the discovery this month.

The feature was videotaped by chance in August 2006, when JAMSTEC researchers were diving aboard their deep-sea research submersible Shinkai 6500, on a press jaunt with a television crew. In a lava dome in the Okinawa Trough, 1,470 metres deep in the southern waters of Japan, where clear, hot fluid was bubbling out of the sea floor, the researchers caught on film the sudden, unexpected emergence of white and blue smoke.

The colour change is undoubtedly due to a change in chemistry in the water, probably caused by a change in magma activity below. But why it is blue, and what that means for researchers' understanding of hotspots, is unclear.

Fire down below

Hydrothermal vents, first discovered in 1977, are essentially geysers on the sea floor. Sea water deep inside the seabed mixes with high-temperature magmatic gas, picking up a high mineral concentration from the surrounding rocks, and jets out from a crack in the sea floor. The fluid, which can be as hot as 400 °C, contains sulphur compounds that can feed a strange variety of local bacterial life.

The colour of the fluid is determined by a number of things, including the temperature and chemistry of the magmatic chamber. At high temperatures, heavy-metal ions can create black sulphides that look like smoke from a chimney. At lower temperatures these can look white. Takai says the blue probably comes from particles of silica in the smoke — although for now that's just a guess.

The JAMSTEC researchers plan to investigate the vent more thoroughly from March. They will use the same submersible to analyse the sea water's chemistry and microbial contents, and plant seafloor seismometers to monitor magmatic and seismic activity.

"We still don't know yet what the blue colour means," says Tetsuro Urabe, a researcher specializing in seafloor hydrothermal systems at the University of Tokyo. "It may be an interesting discovery, but we cannot tell from this single observation."