• hydrothermal plume;
  • acoustic imaging;
  • Doppler velocity;
  • entrainment;
  • volume flux;
  • flow velocity

[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 inline image to inline image above the vents. The time series exhibits temporal variations of the plume vertical volume flux ( inline image), centerline vertical velocity component ( inline image) and expansion rate ( inline image); these variations have major spectral peaks at semidiurnal ( inline image cycle/day) and inertial oscillation ( inline image cycle/day) frequencies. The plume expansion rate (average inline image) is inversely proportional to the plume centerline vertical velocity component (coefficient of determination inline image). 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.