The relative effect of particles and turbulence on acoustic scattering from deep sea hydrothermal vent plumes revisited

Abstract

Author Posting. © Acoustical Society of America, 2017. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 141 (2017): 1446–1458, doi:10.1121/1.4974828.The relative importance of suspended particles and turbulence as backscattering mechanisms within a hydrothermal plume located on the Endeavour Segment of the Juan de Fuca Ridge is determined by comparing acoustic backscatter measured by the Cabled Observatory Vent Imaging Sonar (COVIS) with model calculations based on in situ samples of particles suspended within the plume. Analysis of plume samples yields estimates of the mass concentration and size distribution of particles, which are used to quantify their contribution to acoustic backscatter. The result shows negligible effects of plume particles on acoustic backscatter within the initial 10-m rise of the plume. This suggests turbulence-induced temperature fluctuations are the dominant backscattering mechanism within lower levels of the plume. Furthermore, inversion of the observed acoustic backscatter for the standard deviation of temperature within the plume yields a reasonable match with the in situ temperature measurements made by a conductivity-temperature-depth instrument. This finding shows that turbulence-induced temperature fluctuations are the dominant backscattering mechanism and demonstrates the potential of using acoustic backscatter as a remote-sensing tool to measure the temperature variability within a hydrothermal plume.We thank the National Science Foundation for support (NSF Award Nos. OCE-0824612 and OCE-1234163 to APL-UW; NSF Award Nos. OCE-0825088 and OCE-1234141 to Rutgers)