2019_programme: A PASSIVE ACOUSTIC MEASUREMENT OF OCEAN ACIDITY



  • Session: 14. Environmental acoustics and noise
    Organiser(s): Barclay David
  • Lecture: A PASSIVE ACOUSTIC MEASUREMENT OF OCEAN ACIDITY
    Paper ID: 941
    Author(s): Barclay David, Buckingham Michael
    Presenter: Barclay David
    Presentation type: oral
    Abstract: The absorption of sound in seawater is due to the viscous and chemical relaxation of different compounds. Over the wind noise band of 1 – 10 kHz, the frequency dependence of the absorption is due to the mechanisms of chemical relaxation for magnesium sulfate (f > 3 kHz) and for boric acid (f < 3kHz), which involve ionic dissociations activated and deactivated by the condensation and rarefaction of the medium by passing sound waves. Concentrations of both chemicals determine the level at which the sound is absorbed, which makes the process dependent on the salinity, temperature, and pressure in the ocean. The concentration of boric acid in the ocean is a direct measure of pH, while the concentration of magnesium sulfate is independent of pH, thus a measurement of the frequency dependence of sound absorption may be used to determine ocean acidity. When local winds are strong (> 10 m/s), the ambient noise field is dominated by locally generated surface noise and has a depth-independent directionality and a weakly frequency and depth-dependent intensity, due to sound absorption. By comparing measurements with theory, estimates of ocean acidity can be made from the depth profiles of ambient noise. (Research supported by ONR)
  • Corresponding author: Dr Barclay David
    Affiliation: Dalhousie University
    Country: Canada
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