A closed sea like the Mediterranean has a particular circulation of water, heavily influenced by the winds that can generate surface currents of intensity up to more than 2-3 knots offshore.
Even a closed sea like the Mediterranean has a particular circulation of water, heavily influenced by winds that can generate surface currents of intensity up to more than 2-3 knots offshore . They have little influence on the climate, even though they may be decisive, especially as regards the trend of rainfall over large areas of the Mediterranean .
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The main stream of the Mediterranean
The strong evaporation caused by prolonged sunshine is such that it cannot be compensated by the contribution of fresh water (coming from rivers or from the rain itself). This lack of compensation gives rise to an intense surface current which enters the Atlantic ocean, channeling into the Strait of Gibraltar , towards the Mediterranean basin .
In practice, the presence of this important surface current that moves from west to east continually supplies the central-western Mediterranean sea with less dense ocean water with less salinity than the Mediterranean waters.
This ocean current, fundamental for the Mediterranean rebalancing, after crossing the Strait of Gibraltar, bringing with it algae and ocean fauna, enters the Mediterranean sea, deviating to the right at the height of the Alboran sea, due to the effect of the land rotation.
Where does the Gibraltar current go?
The main branch of this current from the nearby Atlantic flows in front of the Moroccan and Algerian coast, reaching or exceeding the threshold of 1 mile / hour . One branch of it then tends to sink towards the Sicilian Channel, while the other continues between the Sardinian Channel and the lower Tyrrhenian Sea. Although meteorological conditions, particularly when intense winds from the NE and East are activated , can slow it down, the course of this current can be considered almost permanent.
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The main cause of the origin of the famous current, known as the “Mediterranean current” , is to be attributed to the remarkable “salinity gradient” (differences in salinity) and “density” existing between the Atlantic waters is the Mediterranean ones. The waters of the Mediterranean Sea, due to the strong evaporation not compensated by the contribution of water from rivers and rains, have a higher degree of salinity than the oceanic ones and the Strait of Gibraltar.
For this reason they are much denser. In this way the less salty waters of the Atlantic are poured over the Mediterranean and for balance of density, a deep, more salty and dense current will have to go towards the ocean. The same exchange of currents of different densities also takes place between the Black Sea and the eastern Mediterranean . It must be remembered that salinity exceeds 38-39% along the eastern basin of the Mediterranean Sea.
Circulation between the Black Sea and the Aegean Sea
On the Black Sea, on the other hand, due to the supply of fresh water from large rivers and river basins, such as the Danube or the Don , and the poor evaporation, the salinity does not even exceed 15% . A strong imbalance of salinity and density is created with the nearby Mediterranean which tends to be bridged with the formation of a superficial sea current that transports the lighter and less salty waters from the Black Sea to the Aegean Sea, through the Bosporus and the Strait of the Dardanelles. In depth, however, another current is formed, which pushes the saltier and denser waters towards the Black Sea.
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The famous “currents of depth”
Furthermore, recent studies have confirmed the existence of different and complex “depth currents” (abyssal) that are activated periodically on different sectors of the Mediterranean. These “depth currents” arise at the end of the winter season, a period in which the surface temperatures of the waters reach the minimum values, undergoing heavy cooling. The first of these “depth currents” originates after the mistral significantly cools the waters between the Gulf of Lion and the Balearics.
Following the increase in density, the water sinks to the bottom, well over 2000 meters deep, contributing to the slow exchange of deep waters. A second and no less important “depth current” is triggered after the bora, with its impetuous murmur, drastically cools the waters of the Gulf of Trieste and the Adriatic, thus generating a southbound current that sinks below of the Otranto Channel , contributing to the exchange of deep Ionian waters.
