An acoustic remote sensing and submersible study of an Arctic submarine spring plume

Abstract

Results from a field study of a submarine spring and its associated brackish water plume at the head of Cambridge Fiord, Baffin Island, are presented. Computer-enhanced 1920-kHz acoustic backscatter images yield measures of maximum height of rise, plume geometry, and vertical velocities in the rising plume. Submersible observations indicate that the freshwater discharge is localized, being about 5 m in horizontal extent. A thriving benthic community was found within this area. The initial geometry and water properties of the flow at the vent, together with the ambient stratification and a numerical buoyant plume model, are used to show that the probable freshwater discharge rate lies in the range 0.10 to 0.20 m3/s. Computed vertical velocities on the plume axis are significantly greater than the vertical velocities inferred from scattering structure trajectories in the acoustic images. The decay of acoustic backscatter amplitude as a function of radial distance in the neutrally buoyant spreading plume is comparable to the radial decay of temperature fine structure, and the radial decay scales are consistent with those expected from molecular dissipation of turbulent microstructure.Paper number 90JC00208. 0148-0227/90/90JC-00208505.00 reported, including the first direct observations of the vent itself. The purpose of the study was to determine the physical nature of the vent, to quantify the freshwater discharge rate, and to further investigate the relationships between acoustic backscatter and turbulent fine structure in the plume. Our interest in the latter problem stems from the fact that acoustic remote sensing techniques are being used increasingly in connection with a variety of small-scale physical processes in the ocean, and in many instances it has been suggested that turbulent microstructure may contribute to the observed backscatter. Examples include largeamplitude interfacial waves [Proni and Apel, 1975; Haury et al., 1979; Farmer and Smith, 1980], and high-temperature hydrothermal plumes [Palmer and Rona, 1986]. However, the relative contribution to these acoustic images of scattering from turbulence, and from biological or other scatterers often found in association with thermocline or pycnocline zones [e.g., Kaye, 1979], has proved difficult to resolve in most instances. Nevertheless, several studies have shown theoretically that the scattering cross sections for turbulence quantities in the ocean can in some circumstances be comparable to typical cross sections for biological organisms [Munk and Garrett, 1973; Proni and Apel, 1975; Goodman and Kemp, 1981]. Finally, clear evidence for the detection of turbulent microstructure by acoustic backscatter has been obtained in the field in studies of turbulent wakes generated by towed or self-propelled objects in the presence of stratification, with the observed cross sections exhibiting good agreement with theoretical calculations [Pelech et al., 1983; Thorpe and Brubaker, 1983].This paper begins with a presentation of the data from a 3-day experiment in...

Discharge estimation of submarine springs in the Dead Sea based on velocity or density measurements in proximity to the water surface

“…The current formed by a submarine spring has a structure that depends on the physical differences (temperature, salinity, and stratification) between the intrusive groundwater and the surrounding fluid, as reflected in the fluxes of momentum and lift force at the origin. These generate a flow field with a specific structure, temperature (Pantokratoras, 2001), and distinctive velocity and density distributions (Colbourne & Hay, 1990). The structure of the ascending fluid and its flux can be evaluated by measuring physical parameters such as salinity, velocity at the spring orifice, and the height to which the water upwells (Colbourne & Hay, 1990), or it can also be evaluated by a physical model (i.e., Kinoshita, Tabeta, & Tanabe, 2009).…”

“…These generate a flow field with a specific structure, temperature (Pantokratoras, 2001), and distinctive velocity and density distributions (Colbourne & Hay, 1990). The structure of the ascending fluid and its flux can be evaluated by measuring physical parameters such as salinity, velocity at the spring orifice, and the height to which the water upwells (Colbourne & Hay, 1990), or it can also be evaluated by a physical model (i.e., Kinoshita, Tabeta, & Tanabe, 2009). Due to the difficulty to evaluate SGD and because this phenomenon considerably varies in space and time (Bokuniewicz et al, 2008;Povinec et al, 2006;Taniguchi et al, 2006), it is preferable to apply different techniques to varying spatio-temporal scales (Burnett et al, 2003;Tait et al, 2013).…”

The Three Scales of Submarine Groundwater Flow and Discharge across Passive Continental Margins

“…When compared with the nearshore zone, relatively little is known about the dynamics of submarine groundwater systems at this scale. Striking examples terminate in offshore springs, particularly in carbonate settings (Colbourne and Hay 1990;Swarzenski et al 2001;Fleury et al 2007).…”

Forward scattering of a pulsed continuous wave signal through laminar and turbulent thermal plumes

“…Acoustic propagation has been treated by Wenzel and Kellert and more recently by Yang and McDaniel, 5 but, in general the electromagnetic literature has been sited and used where appropriate. Flattd discussed the appropriate r-gions for these applications 6 to ocean acoustics.…”

“…The structure of the plume itself as it becomes turbulent is of interest in order to investigate the trends in the received acoustical data. From Batchelor 26 the weight deficiency produced per unit time at the source (poF) for a laminar plume is given by equation (6).…”