Tuesday 23 August 2005

PB3
1000-1220 hours

145
Turbulent mixing and flow around a small seamount on Kaena Ridge, Hawaii
Carter, Glenn¹, Gregg, Mike¹, Merrifield, Mark²
1 APL, University of Washington, Seattle, WA, USA
2 SOEST, University of Hawaii, USA
Author email: carter@apl.washington.edu
Microstructure observations over a small seamount on the Hawaiian Ridge, showed asymmetry in the along- and across- ridge directions. The approximately 400 m high seamount is atop of the southern edge of the Kaena Ridge, 34 km northwest of Oahu. Comparison with horizontal kinetic energies from a 1 km resolution numerical simulation showed the across-ridge asymmetry correlated to a M² tidal beam emanating from northern edge of the ridge. Whereas, the along-ridge asymmetry was likely the result of undersampling a spatially and temporally varying flow field. Average observed dissipation rates over the seamount were 6.2e-8 W/kg and average diapycnal diffusivities were 1.3e-3 m^2/s. The M² model velocities show that most of the flow goes around, rather than over, the seamount. The flow patterns, however, are more complicated than for an isolated seamount, due to the influence of the 3000m high Kaena Ridge. The model shows two along-ridge coherent tidal beams that intersect the seamount. One directed southward appears to be generated along much of the northern edge of the ridge. Generation of the northern propagating beam is more complex. Dissipation observations along the 1000-m isobath fall on a M² characteristic perpendicular to the edge of the ridge. Streamlines indicate the flow is steered, by the presence of the seamount, over critical topography to the northwest of this survey line which may result in the along-ridge internal tide characteristic.

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