Light at deep-sea hydrothermal vents

Ambient light spectral data were acquired at two deep‐sea hydrothermal vents with a temperature of ∼350°C: the Hole‐to‐Hell site on the East Pacific Rise at 9°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°C than at the 351°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.