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Abstract:
It is known that an overturning circulation develops in the Mediterranean Sea, although substantially weaker and smaller than in the North Atlantic. We use monthly mean fields from a high-resolution ocean reanalysis (1/16º ×1/16º) to explore seasonal and interannual variability of Mediterranena Sea overturning circulation in both depth and water mass parameter spaces (potential density, potential temperature, salinity) from 1987 to 2018. Results show a clear single zonal clockwise transport cell in all three spaces that extends from the Strait of Gibraltar to the Levantine Basin, in which water masses tend to densify as they move eastward. This densification is mainly controlled by salinity in the Eastern Mediterranean basin (EMED), while in the Western Mediterranean (WMED) both salinity and potential temperature variations must be taken into account. In contrast, the meridional overturning transport, much more complex, is able to capture smaller-scale variations better since it responds faster to perturbations in the circulation.
Seasonal variations in overturning transport are reflected in the size and strength of overturning cells in all spaces, being remarkably narrower in winter than in summer. Regarding interannual changes, we show that the zonal overturning transport in density space is significantly correlated with the North Atlantic Oscillation, the Mediterranean Oscillation Index and the Scandinavian pattern during wintertime in the WMED. In contrast, no significant correlations appear in the zonal components of EMED, although the overturning metric in density space captures well the Eastern Mediterranean Transient, that occurred during years 1992–1996.
