Investigations of ambient light emission at deep‐sea hydrothermal vents

Abstract

The Ambient Light Imaging and Spectral System (ALISS) was used to image ambient light from black smokers, flange pools, and a beehive on the East Pacific Rise and the Juan de Fuca Ridge. ALISS is a low‐light digital camera with custom‐designed optics. A set of nine lenses, each covered by an individual band‐pass filter, allows an identical scene to be imaged simultaneously in nine wavelength bands spanning the range of 400–1000 nm. Thus information about both the location and the spectral character of emitting regions is obtained. The primary source of light at deep‐sea vents is thermal radiation due to the high temperature of the hydrothermal fluid. This thermal light peaks in the infrared with a tail that extends into the visible. Data suggest that flange pools have an emissivity of ∼0.9 and black smoker fluids have an emissivity of ∼0.3. Thermal radiation dominates at wavelengths >700 nm (with a photon flux that increases from ∼106photon cm−2 s−1 sr−1at 700 nm to ∼1010 photon cm−2s−1 sr−1 at 1000 nm). Temporally variable light is observed in the 400–600 nm region of the spectrum that is orders of magnitude greater than predicted for a thermal source (i.e., on the order of 104 rather than 10−2–103photons cm−2 s−1 sr−1). This light is probably caused by mechanisms associated with turbulence, mixing and precipitation, such as vapor bubble luminescence, chemiluminescence, crystalloluminescence and triboluminescence. While biological responses to vent light are not yet known, observed light levels are too low to support obligate photosynthesis.