Slope/shelf circulation and cross-slope/shelf transport out of a bay driven by eddies from the open ocean
2009-09,
Zhang, Yu
Interaction between the Antarctic Circumpolar Current and the continental slope/shelf in the Marguerite
Bay and west Antarctic Peninsula is examined as interaction between a wind-driven channel
flow and a zonally uniform slope with a bay-shaped shelf to the south.
Two control mechanisms, eddy advection and propagation of topographic waves, are identified
in barotropic vortex-escarpment interactions. The two mechanisms advect the potential vorticity
(PV) perturbations in opposite directions in anticyclone-induced interactions but in the same direction
in cyclone-induced interactions, resulting in dramatic differences in the two kinds of interactions.
The topographic waves become more nonlinear near the western(eastern if in the Northern
Hemisphere) boundary of the bay, where strong cross-escarpment motion occurs. In the interaction
between a surface anticyclone and a slope penetrating into the upper layer in a two-layer isopycnal
model, the eddy advection decays on length scales on the order of the internal deformation radius,
so shoreward over a slope that is wider than the deformation radius, the wave mechanism becomes
noticeably significant. It acts to spread the cross-isobath transport in a much wider range while the
transport directly driven by the anticyclone is concentrated in space.
A two-layer wind-driven channel flow is constructed to the north of the slope in the Southern
Hemisphere, spontaneously generating eddies through baroclinic instability. A PV front forms in
the first layer shoreward of the base of the topography due to the lower-layer eddy-slope interactions.
Perturbed by the jet in the center of the channel, the front interacts with the slope/shelf
persistently yet episodically, driving a clockwise mean circulation within the bay as well as crossisobath
transport. Both the transports across the slope edge and out of the bay are comparable with
the maximum Ekman transport in the channel, indicative of the significance of the examined mechanism.
The wave-boundary interaction identified in the barotropic model is found essential for the
out-of-bay transport and responsible for the heterogeneity of the transport within the bay. Much
more water is transported out of the bay from the west than from the east, and the southeastern area
is the most isolated region. These results suggest that strong out-of-bay transport may be found near
the western boundary of the Marguerite Bay while the southeastern region is a retention area where
high population of Antarctic krill may be found.