Observations of the volume flux of a seafloor hydrothermal plume using an acoustic imaging sonar

Abstract

[2] We present a 26 day time series (October 2010) of physical properties (volume flux, flow velocity, expansion rate) of a vigorous deep-sea hydrothermal plume measured using our Cabled Observatory Vent Imaging Sonar (COVIS), which is connected to the Northeast Pacific Time Series Underwater Experiment Canada Cabled Observatory at the Main Endeavour Field on the Juan de Fuca Ridge. COVIS quantitatively monitors the initial buoyant rise of the plume from $5 m to $15 m above the vents. The time series exhibits temporal variations of the plume vertical volume flux (1:93 À 5:09 m 3 =s ), centerline vertical velocity component (0:11 À 0:24 m=s ) and expansion rate (0:082 À 0:21 m=m ); these variations have major spectral peaks at semidiurnal ($2 cycle/day) and inertial oscillation ($1:5 cycle/day) frequencies. The plume expansion rate (average $0:14 m=m ) is inversely proportional to the plume centerline vertical velocity component (coefficient of determination R 2 $ 0:5). This inverse proportionality, as well as the semidiurnal frequency, indicates interaction between the plume and ambient ocean currents consistent with an entrainment of ambient seawater that increases with the magnitude of ambient currents. The inertial oscillations observed in the time series provide evidence for the influence of surface storms on the dynamics of hydrothermal plumes.

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

“…5, the dot-dashed curve shows the estimated S v at the centerline of the North Tower plume as a function of the height above the source vents (z). Using the method described in Xu et al (2013), we estimate the centerline value of S v at a given height by fitting a 2-D Gaussian curve to the measured horizontal cross-section of S v at that height and taking the peak value of the Gaussian curve. The dashed curve in Fig.…”

“…In practice, we estimate W along the centerline of the North Tower plume from the Dopplermode data recorded by COVIS following the procedures described in Xu et al (2013) [ Fig. 8(a)].…”

“…where j L ¼ 2p/L is the wavenumber corresponding to the outer scale (L) of the inertial-convective subrange, and the infinite upper limit suggests the integration is over all turbulence scales L. In practice, we determine L as 2b e where b e is the plume's e-folding radius obtained by processing the Doppler-mode data recorded by COVIS following the procedures described in Xu et al (2013) [ Fig. 8(d)].…”

“…(C1), (C7), and (C4). Using the method described in Xu et al (2013), we obtain time-series measurements of the centerline vertical flow rate (W 0 ) and e-folding radius (b e ) of the plume by processing the COVIS Doppler-mode data. In practice, we substitute W 0 and b e averaged over the time series of May 2014 [Figs.…”

Sonar observation of diffuse hydrothermal flows

“…Multibeam sonar observations of hydrothermal flows began with 3‐D imaging of focused flows (“black smokers”) [ Rona et al ., ] and 2‐D images of diffuse flows [ Rona et al ., ]. Methods have been subsequently developed to obtain quantitative information on focused flows, including interaction with ambient current [ Rona et al ., ], volume flux [ Xu et al ., ], and heat flux [ Xu et al ., ]. The present effort seeks to extend this work, following Ivakin et al .…”