On the Southward Motion of Mediterranean Salt Lenses

Abstract

Abstract A new mechanism is proposed to account for the southward motion of salt lenses in the Canary Basin. It relies on the active mixing that is observed at the periphery of such eddies between the warm salty Mediterranean waters of the core and the surrounding fresher and cooler Atlantic waters. Intrusions driven by this thermohaline contrast feed on the eddy potential energy and drain off the eddy volume anomaly. Submitted to the continuous entrainment of its own fluid by the frontal turbulence, the salt lens suffers a velocity divergence at its periphery, induced by a geostrophic adjustment process. This causes in turn a squashing of the density surfaces and the salt lens must then move southward to conserve its potential vorticity, a possibility offered by the spherical nature of the earth. It appears that mixing may load to the coherent latitudinal displacement of an ensemble of fluid parcels on a β plant, while at the same time dissipating the energy of the structure itself.