On the relationship between the water mass pathways and mesoscale variability in the Western Mediterranean Sea

Abstract

The role of mesoscales on the formation and spreading of water masses in the Western Mediterranean Sea (WMED) is studied with an ocean general circulation model. It is found that the model reproduces the major features of the observed mesoscale variability during the preconditioning of the deep convection in the Gulf of Lions, mixing and spreading of deep and intermediate waters and also the large mesoscale eddiess evolution in the Algerian Basin. The instability of the transition zone between old and newly formed deep waters, which takes place after the violent mixing stages of the deep convection, leads to collapse of the mixed patch and formation of mesoscale eddies. Some of these eddies propagate out of the Gulf of Lions transporting deep waters into the Algerian Basin. The rest of the mesoscale eddies filled with newly formed deep waters remain in the Gulf of Lions, and tend to merge, enlarge and reorganize in an area with two or three large cyclonic eddies. After the cyclonic eddies reach the Algerian Basin they interact with the intense mesoscale field existing there. The model data together with the available satellite SLA data reveal a regular westward propagation of mesoscale eddies in the Northern Algerian Basin. This transport together with southward propagation of mesoscale eddies out of the Gulf of Lions is suggesting that the intermediate and deep waters of the WMED are transported westward by mesoscale eddies. Equivalently we can argue the intermediate and deep waters conveyor belt of the WMED is eddy driven.