Deep sea hydrothermal plumes and their interaction with oscillatory flows

The acoustic scintillation method is applied to the investigation and monitoring of a vigorous hydrothermal plume from Dante within the Main Endeavour vent field (MEF) in the Endeavour Ridge segment. A 40 day time series of the plume's vertical velocity and temperature fluctuations provides a unique opportunity to study deep sea plume dynamics in a tidally varying horizontal cross flow. An integral plume model that takes into account ambient stratification and horizontal cross flows is established from the conservation equations of mass, momentum and density deficit. Using a linear additive entrainment velocity in the model ( E = alpha U-m + beta U-perpendicular to) that is a function of both the plume relative axial velocity (U-m) and the relative ambient flow perpendicular to the plume (U-perpendicular to) gives consistent results to the experimental data, suggesting entrainment coefficients alpha = 0.1 and beta = 0.6. Also from the integral model, the plume height in a horizontal cross flow ( U-a) is shown to scale as 1.8B(1/3)U(a)(-1/3)N(-2/3) for 0.01 {\textless}= U-a {\textless}= 0.1 m/s where B is the initial buoyancy transport and N is the ambient stratification, both of which are assumed constant.