school energy&environment

Sea currents

Huge masses of water displace for long distances due to the wind action. The direction of the movement is determined by the earth rotation (Coriolis force), which creates circular movements. In the Atlantic Ocean, regular and constant winds, the trade winds, move superficial water masses towards the Equator where they are diverted to the west by the Coriolis force (North-Equatorial current); when they reach the American continent they are pushed to the north and accumulate in the Gulf of Mexico. The water continues to flow towards the Atlantic ocean and form the Gulf current along the coast of the United States, and then divide into two:

• one current goes towards the Canary islands and starts the tour again, as we have already described;
• the other current moves to the north-east, reaches the north-western coasts of Europe and mitigates their climate.

In polar areas the water cools down, becomes more dense, falls deep down and moves to the Equator. As it gets warmer, it becomes less dense and lighter and tends to rise to the surface. This movement, that forms deep sea-currents, is very slow: it takes even a thousand years to a water mass to go back to the surface. The Mediterranean Sea is very salty as compared to the Atlantic ocean, as a consequence its water is denser. Water masses in the Mediterranean go deep down and enter the Atlantic ocean through the Strait of Gibraltar. Ocean waters, which are lighter, enter the Mediterranean by moving on the surface. The Black sea is connected to the Aegean Sea through the Bosporus strait and the Dardanelles, that is crossed on the surface as its water is less dense and salty. The water that comes from the Aegean Sea is dense and moves deep underwater, but it does not manage to reach the Black sea because the Bosporus is not deep enough. As a consequence, the water exchange in the Black sea is poor and limited.