The Caspian Sea is the world's largest inland body of water. It is a landlocked sea in Asia. Lying between Europe and Asia, it is bounded by Russia from mid-north to mid-west; Azerbaijan to the southwest, Kazakhstan from mid-north to mid-east, Turkmenistan along with southern parts of its eastern coast, and Iran to the south and adjacent corners. There are central Asian steppes to the north and east. The Caspian Sea was once part of the Tethys Ocean but became landlocked about 5.5 million years ago due to plate tectonics. The sea was named for the Kaspi, ancient people who once lived on its western shores. The ancient inhabitants of its coast perceived the Caspian Sea as an ocean, probably because of its large size and saltiness.
The sea is connected to the Sea of Azov by the Manych Canal. In Antiquity, it was called the Hyrcanian Ocean. Other old names for the Caspian Sea include the Mazandaran Sea, Khazar Sea and the Khvalissian Sea.
The Caspian Sea is home to a wide range of species and maybe best known for its caviar, seal, and oil industries. Pollution from the oil industry and dams on rivers draining into it have harmed its ecology.
The Caspian Sea is nearly the size of Japan, covering an area of about 143,000 square miles (371,000 square kilometers). The sea stretches nearly 1200 kilometers (750 miles) from north to south, with an average width of 320 kilometers (200 miles). The sea is shallowest in the north and the deepest in the south. In the north, the average depth is just 13 to 20 feet (4 to 6 meters); on the other hand, in one place in the south, the seafloor lies 3360 feet (1024 meters) below the water's surface. Its gross coverage is 386,400 km2 (149,200 square miles).
The Caspian Sea lies about 28 meters (92 feet) below sea level in the Caspian Depression, to the east of the Caucasus Mountains and to the west of the vast steppe of Central Asia. The seabed in the southern part of the Caspian Sea reaches as low as 1023m below sea level, which is the second-lowest natural depression on earth after Lake Baikal (-1180m).
Three major rivers flow into the Caspian Sea - the Volga, the Ural, and the Terek, all of which enter from the north; their combined annual flow makes up 88% of all river water entering the sea. The Sulak, Samur, Kura, and a number of smaller rivers flow in on the western littoral, contributing about 7% of the flow, and the remainder comes in from Iranian rivers. The eastern littoral is notable for the absence of any permanent streams.
The sea contains as many as 50 islands, most of them quite small. Chechen is the largest island in the northwest, followed by Tyuleny, Morskoy, Kulaly, Zhiloy, and Ogurchin. Ogurja Ada is the longest island in this sea. It is 37 kilometers long and at a maximum, 3 kilometers in width.
The Caspian Sea has a salinity of approximately 1.2% (12 g∕l) which is about a third of the salinity of most seawater. The water of the Caspian Sea contains three times less salt than oceanic water, named Tethis, which connected to the Atlantic and Pacific Oceans 50-60 million years ago. As the gradual shift of continental plates isolated it, the influx of freshwater from rivers, melting ice, and precipitation diluted the salinity of the Caspian Sea.
The sea's basin is usually divided into the North, Middle, and South Caspian, with the divisions based mostly on varying characteristics of the seafloor and water.
The Middle Caspian and most of the South Caspian lie in the warm continental belt, while the North Caspian has a moderately continental climate. The southwest has subtropical influences, while the eastern shores have mainly a desert climate. Summer air temperatures average between 75° and 79° F (24° and 26° C). Winter temperatures range from 14° F (–10° C) in the north to 50° F (10° C) in the south.
Average annual precipitation, falling mainly in winter and spring, varies from 8 to 67 inches (200 to 1,700 mm) over the sea, with the least falling in the east and the most in the southwestern region.
Evaporation from the sea surface reaches as high as 40 inches (101 centimeters) per year. As a result, the sea is very salty in the Kara-Bogaz-Gol Gulf, where much evaporation occurs.
Ice formation affects the northern Caspian, which usually freezes completely by January, and in exceptionally cold years ice that floats along the western shore comes in the south as well.
The Caspian Sea has characteristics common to both seas and lakes. It is often listed as the world's largest lake, although it is not a freshwater lake. It contains about 3.5 times more water, by volume than all five of North America's Great Lakes combined. Lake Superior, Michigan, Huron, Erie, and Ontario form the Great Lakes of North America. The Volga, Ural, and the Terek rivers discharge into the Caspian Sea, but it has no natural outflow other than by evaporation. Thus, the Caspian ecosystem is a closed basin, known as the endorheic basin. Because it has no outflow, the amount of rainfall in the regions of the rivers can greatly impact the water level of the Caspian Sea. Human-constructed dams built during the last two centuries have also changed water levels.
The isolation of the Caspian basin, its climate, and salinity gradients has created a unique ecological system.
About 850 animals and more than 500 plant species live in the Caspian Sea. Considering the size of the Caspian Sea, this is a relatively lower number of species. Most of the animal and plant species found in the Caspian Sea are endemic (i.e. found only there). Blue-green algae (cyanobacteria) and diatoms constitute the greatest biomass concentrations, and there are several species of red and brown algae.
Reptiles native to the sea include spur-thighed tortoise and Horsfield’s tortoise.
The Caspian Sea is home to a variety of fish and aquatic creatures, however, it is mostly known for caviar. More than 90% of the world’s caviar is obtained from the Caspian Sea. Caviar is roe or eggs from the sturgeon family of fish. It's considered a delicacy, often eaten raw as an appetizer, with some caviar fetching a high price. Sturgeon fish is one of the rare aquatic species around the world. Six sturgeon species, the Russian, bastard, Persian, sterlet, starry, and beluga, are native to the Caspian Sea. The sturgeon yield roe (eggs) that are processed into caviar. The value of sturgeon is not for its meat, but because of its eggs, which are known as caviar or “black pearl”. Overfishing has threatened the population of sturgeon. Caviar harvesting further endangers the fish stocks, since it targets reproductive females.
The Caspian Sea is home to a population of seals known as the Caspian seal (Pusa caspica). It is the only marine mammal in the Caspian Sea and is found nowhere else in the world. It is one of the very few species that live in inland waters. Due to the hydrological environment of the sea, it is different from those inhabiting freshwater. At the start of the 20th century, there were around 1 million Caspian seals, but today the population has fallen by more than 90% and continues to decline.
The sea coast provides important sites for many nesting and migratory birds such as flamingoes, geese, ducks, gulls, terns, swans.
Apart from the sturgeon fish (for caviar) and seals (for furs), petroleum and natural gas have become the region's most important resources. The most-promising reserves lie under the northeastern Caspian and its adjacent shores. Minerals such as sodium sulfate, extracted from the Kara-Bogaz-Gol, also have considerable economic importance.
Beluga Sturgeon
The Caspian Sea plays an important role in the region's transportation. Petroleum, wood, grain, cotton, rice, and sulfate are the basic goods carried. Following are the most important ports:
Today the Caspian Sea environment faces significant environmental pressure. Overfishing, discharging wastewater, extraction of gas and oil, and transport activity put great pressure on this unique ecosystem and many Caspian animals and plant life are threatened by over-exploitation, habitat destruction, and pollution.
The level of the Caspian has fallen and risen, often rapidly, many times over the centuries. From 1979-1995, the sea levels increased by about 12 cm (5 inches) per year. Over the past two decades, the sea has been slowly evaporating due to rising temperatures associated with climate change.
The Volga river the largest in Europe, drains 20% of the European land area. It is a major source of the Caspian's inflow. Its lower reaches are heavily developed with numerous unregulated releases of chemical and biological pollutants. The Volga river is one of the principal sources of trans-boundary contaminants into the Caspian.
