Hydrothermal plumes venting from black smokers and diffuse flow discharging from the surrounding area of the seafloor are important as agents of transfer of heat, chemicals, and biological material from the crust into the ocean in quantitatively significant amounts. An unprecedented time series of three-dimensional (3-D) volume images of plumes rising tens of meters from black smoker vents and of concurrent 2-D maps of diffuse flow discharging from surrounding areas of the seafloor illuminates the turbulent behavior of hydrothermal fluid transfer into the ocean.

A cabled observatory vent imaging sonar (COVIS) has been developed to provide plume and Doppler imaging of hydrothermal vents and surrounding diffuse flow. The system was designed to be compatible with the power and data interface standards of the Neptune Canada cabled observatory. COVIS is a 4 m tall, titanium tripod employing a Reson 7125 multibeam sonar. The sonar transducers are positioned by a motor-driven three degree of freedom rotation system (pitch, roll, and yaw). A 400 kHz, 1 x 128 deg fan-beam projector is used with a receiver array that forms 256 beams having horizontal width 0.5 deg and covering a 128 deg azimuthal sector. Volumetric imaging of plumes is generated as the transducer array is scanned in 1 deg pitch steps. Doppler measurements of flow velocity over a 3-D grid are also derived. A 200 kHz, 28 x 128 deg broad beam projector is used to image the diffuse areas near the base of the hydrothermal vent edifices. Software allows for the creation of complex, arbitrary, autonomously executed experiments that control all aspects of the sonar and rotation system. COVIS was successfully deployed in September 2010. The design of COVIS provides insights relevant to future cabled acoustic systems.