THE ghostly glow lighting deep-sea vents is caused by a simple chemical reaction, researchers in the US suggest. Their experiments, which recreate the environment of hydrothermal vents, may resolve a puzzle that has dogged scientists for more than a decade.
Oceanographers first detected faint light from hydrothermal vents in the ocean floor 11 years ago. Most of the light is thermal radiation from the hot vent water. But the heat cannot account for some of the shorter wavelength light, which is an orange-yellow colour. Attempts to explain what produces this light have ranged from the tiny flashes that occur as minerals crystallise to the collapse of bubbles under the pressure of the abyss (see "The light at the bottom of the sea", New Scientist, 13 December 1997, p 42).
But now David Tapley of Salem State College in Massachusetts and Malcolm Shick of the University of Maine at Orono have stumbled on an alternative explanation by simulating the conditions at the vents. The researchers were studying how the water that erupts from the vents, which is rich in dissolved sulphide, mixes with the oxygenated seawater around the vent. Mixing a powerful reducing agent such as sulphide with an oxidant can create free radicals-highly reactive molecules that are hazardous to life-and the researchers hoped to find out if radicals form in the vents.
But during the experiments, Tapley noticed that the reaction was faintly luminescent (The Biological Bulletin, vol 196, p 52). Although the light was too feeble to measure its spectrum, Tapley detected it with a photomultiplier sensitive to light across visible wavelengths. "We suspect strongly that chemiluminescence from sulphide oxidation is the source of the enigmatic light at vent sites," says Shick.
The idea could also explain another puzzle-why the glow at vents sometimes seems strongest ten centimetres or so away from the vent openings. This zone is often where the sulphide-laden water from the vent ploughs into the oxygenated seawater.
"It's very early days yet, but this is a promising direction for people to be going in," comments Joe Cann, a geologist at the University of Leeds. "I look forward to measurements of light intensity and a spectrum from the reaction." The eerie glow of deep-sea vents may have driven the first steps in the evolution of photosynthesis, and Cann has been looking for traces of photosynthetic pigments at modern vents.
Author: Jon Copley
New Scientist magazine, issue 20 March 1999
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