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



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