The Paratethys Sea, which existed about 34 million years ago, is also known as the largest lake the world has ever seen. This great transcontinental strip of water stretched along the southern edge of Eurasia from present-day Austria to Turkmenistan and covered an enormous area of 2.8 million square kilometers.
Paratethys, originally a sea, was formed by the uplift of orogenic belts in the Alps and Carpathians. This uplift resulted in the formation of a basin with a southern connection to the Mediterranean. However, about 12 million years ago, a collision between the African and European tectonic plates caused this connection to close, leading to the reclassification of Paratethys as a lake.
Paratethys contained 1.77 million cubic kilometers of water, about 10 times the sum of all today’s lakes. Although the Paratethys had a larger surface area than the Mediterranean, it had about half the volume of the Mediterranean’s 3.75 million cubic kilometers of water due to its surprisingly shallow nature.
While the Mediterranean was once fed with fresh water through the many rivers and streams of inland Europe, the separation of the Paratethys cut off this source and instead freshwater streams diverted to the lake. With this change, the region has experienced a transition from the wide variety of marine species it previously had to a less diverse freshwater species, and there has been a significant change in the flora and fauna of the region.
Paratethys also changed the climate of the region
Paratethys’ size also meant it had a significant impact on the Eurasian climate. The water vapor created by the lake contributed to reducing the thermal difference between the seasons, promoting a much more stable seasonal climate.
However, the Paratethys lake did not last long, and during a period of “over-drying” with little rainfall in Eurasia, the isolated waters of the lake, which could not be filled with precipitation, evaporated.
Between 9.8 and 7.7 million years ago, water levels dropped by about 250 meters during a period called the Great Hersonian Dry, when most of the water evaporated. This caused the lake to lose 70 percent of its surface area and 30 percent of its volume, reducing it to the size of today’s Black Sea.
Drying has also affected the region’s established ecosystem. Dolphins, seals, and even the world’s smallest whale species (Cetotherium riabinini) that once lived in Paratethys can no longer survive in the lake’s receding waters.
The shrinkage has also affected the Eurasian climate, and the once steady thermal gradient has been replaced by much colder winters and warmer summers.
Legacy of Paratethys: Black Sea, Caspian Sea and Aral Sea
As the paratethys continued to shrink, it formed three distinct regions that still exist today. Between Eastern Europe and Western Asia, the Black Sea covers an area of 436,000 square kilometers. Covering an area of 371,000 square kilometers in the Middle East, the Caspian Sea is currently the world’s largest inland body of water. And finally, there is the Aral Sea, which currently covers 68,000 square kilometers but continues to shrink as a result of its own drying period caused by human activity…
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