Entrainment and horizontal cross flows and their affect on hydrothermal plume vertical velocity and temperature fluctuations -- Dr. Daniela Di Iorio
2011-02-10 16:00 - 17:00 (US/Eastern) | Physics 202
Departmental Colloquium. Deep sea hydrothermal plumes are driven by gravitational buoyancy forces and may rise up to hundreds of meters above their orifice. Ambient ocean water is entrained into the plume during its ascent, which makes the plume diluted and cooled. Long term measurements of physical properties of hydrothermal plumes are limited and are important for understanding heat flow from the Earth’s interior. In Sept 2007 an acoustic scintillation system was used to specifically quantify the temporal variability of the vertical velocity and temperature fluctuations of the hydrothermal plume of Dante at 2155m depth. Six weeks of data was collected and using the space-time coherence of the acoustic amplitude signal, hourly vertical velocity measurements were obtained. Theoretical developments comparing acoustic forward scattering from turbulence and from particles show that suspended particles within the plume produce negligible amplitude fluctuations compared to turbulence modeled by an isotropic and homogeneous Kolmogorov model for the temperature variability.The vertical velocity and temperature fluctuations show a significant negative correlation with the horizontal flow. The hydrothermal plume of Dante and its interaction with the horizontal ﬂow within the Main Endeavour Field can be generalized as follows: 1) when the horizontal ﬂow is weak (during the ebbing tide), less ambient ocean water is entrained into the plume. In such a case, the plume is faster and hotter and the temperature ﬂuctuations increase within the plume; 2) when the horizontal ﬂow is strong (during the ﬂooding tide), more ambient ocean water is entrained into the plume. In such a case, the plume is slowerand cooler with reduced temperature fluctuations. Results from an integral plume model based on the conservation equations of mass, momentum, density deﬁcit and dissolved tracers and taking into account ambient stratification and horizontal cross flows are compared with observations showing consistent results.
