The cabled observatory vent imaging sonar deployed on the Ocean Observatories initiative’s cabled array

Abstract

The Cabled Observatory Vent Imaging Sonar (COVIS) was installed on the Ocean Observatories Initiative’s Cabled Array observatory at ASHES hydrothermal vent field on Axial Seamount in July 2018. Diffuse hydrothermal flows are identified by maps made using the standard deviation of thephase change between pings separated in time by fractions of 1 s. The results demonstrate significant influences of ocean tides and bottom currents on diffuse hydrothermal discharge. The same data are used to estimate diffuse heat flux, providing two-dimensional maps of heat flux density at a rate of one per day. Sonar data are also used to generate three-dimensional backscatter images of the buoyant plumes above major sulfide structures. These backscatter images show substantial changes in plume bending in the presence of ambient currents and potentially the variations of outflow fluxes. The intensity of acoustic backscatter decreases significantly for highly bent plumes as compared to nearly vertical plumes, reflecting enhanced mixing of plume fluids with seawater driven by ambient currents. A forward model of acoustic backscatter from a buoyancy driven plume yields a reasonable match with the observation, paving the way for inversely estimating the source heat flux of a hydrothermal plume. [Work sponsored by NSF.]