The relative effects of particles and turbulence on acoustic scattering from deep-sea hydrothermal vent plumes

Acoustic methods are applied to the investigation and monitoring of a vigorous hydrothermal plume within the Main Endeavor vent field at the Endeavor segment of the Juan de Fuca Ridge. Forward propagation and scattering from suspended particulates using Rayleigh scattering theory is shown to be negligible (log-amplitude variance σχ2~10-7) compared to turbulence induced by temperature fluctuations (σχ2~0.1). The backscattering from turbulence is then quantified using the forward scattering derived turbulence level, which gives a volume backscattering strength of sV = 6.5 × 10−8 m−1. The volume backscattering cross section from particulates can range from sV = 3.3 × 10−6 to 7.2 × 10−10 m−1 depending on the particle size. These results show that forward scatter acoustic methods in hydrothermal vent applications can be used to quantify turbulence and its effect on backscatter measurements, which can be a dominant factor depending on the particle size and its location within the plume.