Dynamics of advection‐driven upwelling over a shelf break submarine canyon

Abstract

[1] The response over a submarine canyon to a several day upwelling event can be separated into three phases: an initial transient response; a later, much longer, "steady" advection-driven response; and a final relaxation phase. For the advection-driven phase over realistically steep, deep, and narrow canyons with near-uniform flow and stratification at rim depth, we have derived scale estimates for four key quantities. Observations from 5 real-world canyon studies and 3 laboratory studies are used to validate the scaling and estimate the scalar constant for each scale. Based on 4 geometric parameters of the canyon, the background stratification, the Coriolis parameter, and the incoming current, we can estimate (1) the depth of upwelling in the canyon to within 15 m, (2) the deep vorticity to within 15%, and (3) the presence/absence of a rim depth eddy can be determined. Based on laboratory data, (4) the total upwelling flux can also be estimated. The scaling analysis shows the importance of a Rossby number based on the radius of curvature of isobaths at the upstream mouth of the canyon. This Rossby number determines the ability of the flow to cross the canyon isobaths and generate the pressure gradient that drives upwelling in the canyon. Other important scales are a Rossby number based on the length of the canyon which measures the ability of the flow to lift isopycnals and a Burger number based on the width of the canyon that determines the likelihood of an eddy at rim depth. Generally, long canyons with sharply turning upstream isobaths, strong incoming flow, small Coriolis parameter, and weak stratification have the strongest upwelling response.Citation: Allen, S. E., and B. M. Hickey (2010), Dynamics of advection-driven upwelling over a shelf break submarine canyon,

The vertical structure of the circulation and dynamics in Hudson Shelf Valley

“…Since Hudson Shelf Valley is in shallow water over the continental shelf and it extends nearly to the coast, it experiences a wider range of stratification and the bottom boundary layer plays a more fundamental role in the dynamics compared to larger canyons in deeper water. In particular, the vertical scale of the flow in Hudson Shelf Valley is set by the height of the bottom boundary layer, rather than the vertical scale for a stratified flow related to the Burger number, where W is a canyon width scale and N is the buoyancy frequency [ Kampf , ; Allen and Hickey , ]. The scale height is not correlated with the observed …”

“…Several scalings have been proposed for the upwelling transport in deep canyons incising continental slopes [ Mirshak and Allen , ; Kampf , ; Allen and Hickey , ]. While the scales differ substantially [see Kampf , ; Allen and Hickey , ], they depend on a power law where the along‐slope current is raised to the 8/3 [ Mirshak and Allen , ], squared [ Kampf , ], or cubed [ Allen and Hickey , ]. The relationship between wind stress and along‐valley transport in Hudson Shelf Valley is linear for moderate wind stresses (Figure ).…”

Upwelling induced by the frictional stress curl and vertical squeezing of the vortex tube over a submerged valley in the East China Sea

“…The circulation amplifies the upslope transport at the head and at the downstream rim of the submarine canyons [ Kämpf , ]. The strength of the is determined by a Rossby number, which is based on the radius of curvature of the isobaths at the upstream rim of the canyon [ Allen and Hickey , ]. The bottom Ekman process induces the cross‐canyon transport.…”

Impact of the continental shelf slope on upwelling through submarine canyons

“…The deeper flow, initially along the continental slope, turns into the canyon, flows along the canyon against the downstream canyon wall and upwells (under the shelf flow) at the canyon head and along the downstream rim near the head [AH] (blue line in Figure 1). This flow is thick on the downstream side and pinched to nearly zero thickness on the upstream side [Hickey, 1997;Allen and Hickey, 2010;Dawe and Allen, 2010]. Below the slope water that is upwelled, flow in the canyon is toward the head on the downstream side and returns toward the ocean on the upstream side of the canyon leading to deep cyclonic vorticity [Hickey, 1997;Allen and Hickey, 2010] (orange line in Figure 1).…”