Wåhlin
A. K.
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Laboratory observations of enhanced entrainment in dense overflows in the presence of submarine canyons and ridges
Wåhlin
A. K.
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The continental slopes in the oceans are often covered by small-scale topographic
features such as submarine canyons and ridges. When dense plumes, flowing
geostrophically along the slope, encounter such features they may be steered downslope
inside and alongside the topography. A set of laboratory experiments was conducted at
the rotating Coriolis platform to investigate the effect of small-scale topography on plume
mixing. A dense water source was placed on top of a slope, and experiments were
repeated with three topographies: a smooth slope, a slope with a ridge, and a slope with a
canyon. Three flow regimes were studied: laminar, waves, and eddies. When a ridge or a
canyon were present on the slope, the dense plume was steered downslope and
instabilities developed along the ridge and canyon wall. This happened regardless of the
flow characteristics on the smooth slope. Froude and Reynolds numbers were estimated,
and were found to be higher for the topographically steered flow than for flow on smooth
topography. The stratification in the collecting basin was monitored and the mixing
inferred. The total mixing and the entrainment rate increased when a ridge or a canyon
were present. The difference in mixing levels between the regimes was smaller when
topography was present, indicating that it was the small-scale topography and not the
large-scale characteristics of the flow that determined the properties of the product water.