There are wide variations in the salinity of the partially enclosed seas of the Atlantic Ocean

There are wide variations in the salinity of the partially enclosed seas of the Atlantic Ocean. The Mediterranean Sea is an east-west trending body of water with a very irregular coastline. It is surrounded by land on all sides except for a narrow connection, with the Atlantic Ocean through the Strait of Gibraltar.

Atlantic water enters this sea through the strait as a surface flow. In fact, the surface flow from the Atlantic is carried in to replace surface water evaporated at a high rate in the very dry eastern end of the Mediterranean Sea, where the water level is about 15 cm lower than at the Strait of Gibraltar.

Most of the Mediterranean water has salinity varying from 38% to 39%. However, maximum salinity is encountered in the surface waters at the east end of the sea, where it is in excess of 39%.

After sinking and moving as intermediate water towards the Atlantic Ocean there is a gradual decrease in salinity (37.3%.) as it flows over the sill at Gibraltar at a depth of about 165 fathoms. There are many more factors which contribute to the high salinity of this sea.

The rivers falling into this sea do not bring enormous quantity of fresh water. Besides, being situated in the Mediterranean type of climate, summers are dry, the temperatures very high and the sky is clear with the result that rate of evaporation is very high. The cumulative effect of all these factors is a very high salinity (39%) of the surface water of this sea.

The Black sea is a very nearly closed body of water that lies to the north of the Mediterranean Sea. The Black Sea has been rightly described as a catchments area for a large part of the surrounding continent of Eurasia. Here precipitation and runoff into the Black Sea exceed the amount of evaporation.

That is why the surface salinity in this sea is low (16%). However, when the low salinity surface water of this sea passes out through the Bosporus and Dardanelles to the Mediterranean, its high velocity water causes turbulence and vertical mixing. So by the time this low salinity water reaches the Mediterranean, its salinity is increased (30%).

The North Sea offers a very typical and interesting example of variations in the surface salinity in different parts of the same sea. Because of dilution of sea water by river water near coast, salinity in the coastal water is as low as 34.2%.

While, on the other hand, salinity is much higher in the water which has entered from the Atlantic into this sea via the English Channel or around northern Britain. Here the salinity is relatively higher (35%).

The Baltic Sea is partly surrounded by land and is connected with the North Sea by a narrow opening. Being situated in cool temperate climate the rate of evaporation is low.

Besides, the rivers falling into it supply large quantity of fresh water. Therefore the surface salinity in this sea is very low (7%). The surface salinity in the Gulf of Bothnia, the northern part of this sea, is still lower reaching 2%.

The Gulf of Mexico as well as the Caribbean Sea, because of the accumulation of warm and saline equatorial waters, is characterized by high surface salinity (36%).