Dynamics of the Mediterranean salinity tongue

• Main Authors: Stephens, J, Marshall, D
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Antarctic; Antarc*; Labrador Sea; North Atlantic
• Online Access: https://doi.org/10.1175/1520-0485(1999)029<1425:DOTMST>2.0.CO;2; https://ora.ox.ac.uk/objects/uuid:fc14a254-e494-491f-af05-9655a8e29a15

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 wind field 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 parameterization of meddies. The upper-layer depth from the 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 southwestward from the eastern boundary and extending westward into the interior, and provides the pathways along which Mediterranean Water spreads into the model interior. The authors 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 wind forcing 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. A simple parameterization of meddies in the model is also included. 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.