Light at deep-sea hydrothermal vents

Ambient light spectral data were acquired at two deep-sea hydrothermal vents with a temperature of similar to 350 degrees C: the Hole-to-Hell site on the East Pacific Rise at 9 degrees N and the Snake-Pit site on the Mid-Atlantic Ridge. Measurements were made with a simple, multi-channel photometer which simultaneously detected light in four 100 nm-wide bands over the wavelength range of 650-1050 nm. Most of the light detected is near-infrared (750-1050 nm), but there is a 19x greater photon flux than expected from thermal radiation alone at shorter wavelengths (650-750 nm) at the Hole-to-Hell vent. At Snake Pit, more light in the 750-850 nm band was observed 10 cm above the orifice where the temperature was 50-100 degrees C than at the 351 degrees C vent opening. These data suggest the presence of non-thermal light sources in the vent environment. Some possible non-thermal mechanisms are identified, but further data will be required to resolve them.