MECHANISM FOR LOW-FREQUENCY VARIABILITY AND SALT FLUX IN THE MEDITERRANEAN SALT TONGUE

The role of baroclinic instability in the generation of low-frequency variability in the interior of ocean subtropical gyres and its possibl e importance in the zonal flux of salt and heat within the Mediterrane an salt tongue are discussed. The observed zonal enhancement of the lo w-frequency variability is interpreted as the signature of baroclinic instability of the large-scale wind-driven flow. The zonal orientation results from the relatively weak vertical shear of the large-scale up per ocean flow and the stabilizing influence of the planetary vorticit y gradient. There is a reversal in the vertical shear of velocity at m iddepths in the eastern basin of the North Atlantic that results in a local middepth maximum in the zonal eddy flux of density. Linear theor y predicts a vertical structure of this density flux that is nearly co incident with the observed vertical distribution of the warm, salty wa ter of the Mediterranean salt tongue. A primitive equation model is us ed to investigate the nonlinear, large-amplitude regime. The zonal edd y density (or salt) flux averaged over several wavelengths and several cycles of wave growth and breaking indicates that this mechanism may be an important component in the overall salt balance in this region.