Climate evolution in the Mediterranean Sea from an ocean circulation model

The present and future evolution of the Mediterranean Sea hydrographical conditions are investigated using a Mediterranean Sea circulation model forced by a set of atmospheric fields at the sea surface and ocean fields at the neighbouring Atlantic Ocean west of the Strait of Gibraltar. The forcing fields originate from the Med-CORDEX, CMIP5 and CMPI6 data bases and the ORAS4 reanalyses. The simulations cover the period 1950-2100. The results confirm the Mediterranean Sea future warming and saltening but with a large spread among the simulations for this variable. The different contributions to the sea level change are estimated from the simulations. The total sea level is projected to increase by around 500-800 mm in 2100. The contribution of the dynamic part does not exceed 100 mm while that equilibrating the steric part in the Atlantic area is around 250-400 mm; the remaining part due to other contributions being of the order of 250-300 mm. The component which does not equilibrate the steric sea level in the Atlantic area is evaluated between -200 and + 200 mm. At the sea surface the simulations reproduce the northward extension of the Atlantic waters to the north of the Balearic Islands. The thermohaline circulation examined through an east-west vertical section is characterized by enhanced penetration of Atlantic waters at the upper layers and by a tongue of increased salinity in the Levantine Intermediate water deepening from east to west. While the overall density of the Mediterranean Sea is projected to decrease, the density difference between the inflowing and outflowing waters is projected to increase, mainly due to an increase in the temperature and a decrease in the salinity of the Atlantic waters, hence explaining the mass and heat enhanced exchange. It also gives an explanation to the projected increase of the basin sea level drop relative to that in the Atlantic Ocean reproduced in some of the results of the present work.