Dynamics Of The Mediterranean Salinity Tongue
J. C. Stephens and D. P. Marshall, 1999, J. Phys. Oceanogr., 29,
1425-1441.
Abstract
A reduced-gravity planetary-geostrophic model of the North Atlantic, consisting of two active layers overlying a motionless abyss is developed to investigate the effect of the windfield in shaping the dynamics of the Mediterranean salinity tongue. The model is driven by climatological winds and eastern-boundary ventilation in a basin of realistic geometry and includes a parameterisation of meddies.
The upper-layer depth from our model shows a clear similarity to observations, both in terms of the location and intensity of the subtropical gyre and also the position of the outcropping line in the northern basin. Potential vorticity in layer two reproduces the sweep of potential-vorticity contours southwestwards from the eastern boundary and extending westwards into the interior, and provide the pathways along which Mediterranean Water spreads into the model interior.
We solve for the steady salinity field in the second layer, including sources of Upper Labrador Sea Water and Antarctic Intermediate Water on the isopycnal surface. The shape and spreading latitude of the model salinity tongues bear a striking resemblance to observations. Both the windforcing, and the occurrence of a mean transport of Mediterranean Water away from the eastern-boundary, are crucial in obtaining a realistic salinity tongue. The salinity tongues are remarkably stable to variations in the Peclet number.
We also include a simple parameterisation of meddies in the model. Where meddies are dissipated locally by collisions with topographic seamounts, for example, they may generate large recirculations extending across to the western boundary. The net effect of these recirculations is to shift the salinity tongue equatorward.
