On the 12th of August, Turkmenistan and other Caspian states celebrate International Caspian Sea Day. This date was not chosen by chance: on the 12th of August, 2006, the Framework Convention for the Protection of the Marine Environment of the Caspian Sea (Tehran Convention) entered into force.
The Caspian Sea, unique in a number of parameters and 6 million years old, still holds many secrets and mysteries. One of its amazing features is the salt composition of the water.
It is a well-known fact that the Caspian Sea is the largest closed water body on Earth, which is fed by the waters of large and small rivers. The largest of them are the Volga, Ural, Terek, Sulak, Samur.
The rivers flowing into the Caspian bring fresh water. However, this water dissolves salts and minerals from the soil and rocks, which leads to an increase in overall salinity.
And although the Caspian is cut off from the World Ocean, its salinity is also explained by the fact that it is a remnant of the ancient Tethys Ocean. There are many salt marshes and salt domes around it.
At the same time, the salinity of the Caspian water is uneven. The highest salinity levels of up to 11-13 ppm are achieved in the southeast and from 0.05 ppm near the mouth of the Volga.
For example, the Garabogazkol lagoon has a completely different type of salinity than that observed in the Caspian Sea. In the early 1980s, the concentration of Glauber's salt (mirabilite) here reached 310 ppm. Such indicators are comparable to one of the saltiest bodies of water on the planet - the Dead Sea (an endorheic salt lake).
In the Garabogazkol bay, which is also called «the sea of white gold», there are large deposits of mineral salts, in particular, sodium sulfate. The bottom sediments contain magnesium salts, sulfates and other useful materials that can be used in the chemical industry, for example, for the production of fertilizers for agriculture.
The flow of water from the Caspian Sea to the bay of Garabogazkol leads to a decrease in the concentration of salt (salinity) in the Caspian Sea itself. Thus, the waters of the Caspian Sea have a significantly lower salinity compared to ocean water, which has a certain level of salinity (on average about 35 ppm).
Therefore, this indicates that the Caspian Sea is not only one of the largest inland water bodies, but also a water body with unique hydrological and chemical characteristics.
