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Spin-up over steep topography and the effects of a submarine canyon

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Title: Spin-up over steep topography and the effects of a submarine canyon
Author: Mirshak, Ramzi
Degree Master of Science - MSc
Program Earth and Ocean Sciences
Copyright Date: 2001
Abstract: Submarine canyons are common bathymetric features that cut into the continental shelf from the continental slope. During upwelling favourable conditions over the continental shelf, submarine canyons display enhanced upwelling, heavily impacting shelf-slope mass exchange. In this thesis, laboratory experiments were conducted to quantify how velocity, stratification and rotation affect canyon upwelling. Currents were forced by changing the rotation rate of an already rotating tank. Over time, the forced currents evolve, or spin-up, until the fluid within the tank is once again rotating at the same rate as the tank itself. A difference in the spin-up behaviour is observed when a canyon is not present in the laboratory topography. The dynamics that govern flow evolution when a canyon is not present are Ekman suction and diffusion, both of which can be affected by a sloped bottom boundary layer. A numerical model is developed that replicates the spin-up of a stratified fluid over the changing slopes of the laboratory topography in the absence of a canyon, incorporating both the decay of Ekman suction and the change in the diffusion of momentum which occur as the boundary layer flow is arrested by buoyancy effects. Observed spin-up with a canyon present is compared to predicted spin-up without a canyon. The difference measures a force imposed by the canyon, which is found to be proportional to U[sup 2.5]f[sup 0.5]/N, where U is the shelfbreak velocity, f is the Coriolis frequency and N is the buoyancy frequency. This force relates to the flux of water crossing the shelfbreak through the canyon. The results are applied to Astoria canyon, suggesting that in a strong upwelling event, the flux of water through the canyon is 1.3 x 10 ⁵m³ s⁻¹ , nearly 20 times larger than wind-induced upwelling over a similar length of the shelfbreak.
URI: http://hdl.handle.net/2429/11840
Series/Report no. UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/]

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