A three layer, quasi-geostrophic model was developed and applied to study Meddy behavior near seamounts, with a view towards quantifying Meddy-seamount impact on the Mediterranean salt tongue. A point vortex method was defended and derived. We found Meddies are surprisingly able to survive seamount encounters as coherent vortices. Destruction is the exception, rather than the rule. The reason for this is that Meddies dynamically are strong potential vorticity anomalies, and it is difficult to destroy such anomalies. Even though they may be geometrically disrupted by topographic obstacles, as they depart the topographic zone, the anomalies survive. Strong like-signed anomalies have a strong tendency to reorganize and merge. Like-signed patches have a tendency to resist distortion and therefore can hold themselves together when confronted with topographically induced shearing stresses. Such survival have been recognized as central vortex process for roughly 30 years (Christiansen and Zabusky, 1973). The relevant point here is that it is easy to believe their role will transcend our particular illustration, suggesting that our results are robust.
With these results, we estimate that the Meddy-driven mass flux will be a significant effect in shaping the mean salt tongue gradient. Also, Meddy-seamount impact can provide one-quarter to one-hald of the salinity flux divergence necessary to maintain the salt tongue.
If this is true, we then argue Meddy survival is an important limiting factor for the global Mediterranean tongue strength. We estimate somewhere between one quarter to one half of the required global salt anomaly rate can be supplied by Meddy-seamount interaction. It appears that locally, the salt tongue can be controlled by Meddy-seamount interaction near the Horseshoe seamounts, but that this mechanism becomes one of several inputs needed to sustain the salt tongue near the Azores Plateau. These local results are consistent with salt tongue maps.
A summary message then of this work is that Fickian tracer diffusion parameterizations are indeed criticized, but not to the point of exclusion. A decidedly non-classical salt transport mechanism, involving coherent vortex transport and their interaction with seamounts, does look like it is a significant input into the Mediterranean salt tongue. On the other hand, it is probably not the only source of the high tongue salinity; the remainder may be well modeled by down gradient effects.