Timothy J. Crone; William S.D. Wilcock; Andrew H. Barclay; Jeffrey D. Parsons

“ The equation of state for hydrothermal fluid at high temperatures and pressures predicts a significant volume decrease when this fluid mixes and exchanges heat with ambient seawater [18] . This process will produce monopole acoustic radiation with the source located in the jet mixing region some distance above the vent orifice. To the best of our knowledge, this sound source mechanism has not been investigated, thus there is no theory to quantify the magnitude of the pressure perturbations it may generate. ”

“ Abstract Hydrothermal flow through seafloor black smoker vents is typically turbulent and vigorous, with speeds often exceeding 1 m/s. Although theory predicts that these flows will generate sound, the prevailing view has been that black smokers are essentially silent. Here we present the first unambiguous field recordings showing that these vents radiate significant acoustic energy. The sounds contain a broadband component and narrowband tones which are indicative of resonance. ”

“ The acoustic detection of vent locations could help an organism avoid damage from hot hydrothermal fluid, and could provide foraging or reproductive benefits by helping an organism find food or a mating partner. ”

“ One hydrophone was affixed to the instrument's titanium pressure case, and the other had a 3 m cable and was attached to a bracket allowing it to be positioned just a few centimeters from a black smoker vent orifice. We refer to these two hydrophones as the “case” and “remote” hydrophones, respectively. The first-generation system, used in 2004, sampled on three channels continuously at 1000 Hz with a 12-bit A/D converter and a fixed gain for each channel. ”

“ It is played in real-time (i.e. without time stretching or pitch shifting) . Because much of the acoustic energy falls below ∼100 Hz, speakers with good bass response are required to properly reproduce the sound. Most laptop speakers will not produce sound. (0.96 MB WAV)
Movie S1 Movie showing the black smoker acoustic recording system deployed at the Sully vent in September 2004 with audio from the same deployment. The audio and video are not contemporaneous because the remotely-operated vehicle carrying the video camera generated excessive noise. ”

“ Among the many possible resonators are Helmholtz resonators, half-wave or quarter-wave resonators, and solid structures such as tubes, plates, or cavities within the chimneys [24] – [25] . Considering the typical acoustic properties of black smoker fluids, and the geometry of these structures, the frequencies of the observed resonant signals are reasonable. ”