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Title: Shear-induced vertical mixing in the Wyville Thomson Basin : a study of its driving mechanisms, strength and influence
Author: Venables, Emily Joanne
ISNI:       0000 0004 2717 4991
Awarding Body: University of Aberdeen
Current Institution: University of the Highlands and Islands
Date of Award: 2011
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Parameterization of diapycnal mixing is required for accurate modeling of ocean circulation. Almost 50% of all warm Atlantic water flowing towards the Arctic and more than 20% of the returning cold water passes through the Faroese Channels. Diapycnal mixing in the Wyville Thomson Basin (WTB), at the centre of the Faroese Channels, removes heat from Atlantic water flowing northwards and preconditions the cooler waters flowing south over the Wyville Thomson Ridge (WTR). Direct measurements of the dissipation rate of turbulent kinetic energy (epsilon) were obtained from the WTB in September 2007 along with CTD, LADCP and mooring data. Microstructure profiles to a depth of 800m were used to estimate diapycnal diffusivity from epsilon. Large values of epsilon (10-5 Wkg-1) were observed and diffusivity (10-2m2s-1) calculated at approximately 500m depth in a water column depth of 900m. Elevated values coincided with a very strong thermocline between surface Atlantic and cold deep waters in the WTB. Oscillations within mooring data show large O (100m) vertical displacements of the thermocline with a semidiurnal period, hence generation and breaking of tidally forced internal waves by interaction with the ridge topography is proposed as an explanation for observed high diffusivity. Non-hydrostatic 2D model data are used to explore generation and breaking mechanisms of such waves and it is shown that the WTR is an effective generator of internal tides and furthermore that baroclinic energy is trapped and dissipated within the WTB. Conservative calculation of a basin-wide diffusivity (2.51 x 10-4 m2s-1) exceeds that required to maintain global ocean circulation, but heat flux into the dense layer (~14 Wm-2) is found to influence the Faroe-Bank Channel outflow volume by <2%.
Supervisor: Inall, Mark ; Sherwin, Toby Sponsor: NERC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Internal waves ; Turbulence ; Ocean circulation