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

Demirov, Entcho K. and Pinardi, N. (2007) On the relationship between the water mass pathways and eddy variability in the Western Mediterranean Sea. Journal of Geophysical Research, 112 (2). pp. 1-21. ISSN 2156-2202

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Abstract

The role of eddies on the formation and spreading of water masses in the Western Mediterranean Sea is studied with an ocean general circulation model. The model is forced with interannually variable surface forcing for the years from 1979 to 1999. It is found that the model reproduces the major features of the observed mesoscale variability in the Gulf of Lions and the large eddies evolution in the Algerian Basin. The seasonal evolution of circulation in the Gulf of Lions and processes of spreading of newly formed intermediate deep waters in the postconvection period is studied for years 1987 and 1992. The model results are compared with data from observations. It is shown that 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 and enlarge. After the cyclonic eddies reach the Algerian Basin they interact with the intense mesoscale field existing there. The energy analysis shows that the winter and spring are seasons of intensified baroclinic instability of the mean flow in the two regions of interest, the Gulf of Lions and Algerian Basin. The kinetic energy is released by baroclinic instability in spring and summer. The spring spectra in the two regions have maximums at horizontal scales of about 80-100 km which is the typical scale of the eddies in the model. These eddies propagate a cyclonic circuit. The resulting eddy-induced mass transport in deep and intermediate layers is directed out of the Gulf of Lions and toward the Gibraltar Strait. Equivalently, we can argue the intermediate and deep waters conveyor belt of the Western Mediterranean Sea is eddy-drive.

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