The photo is sourced from magput.ru
The Caspian Sea is the world’s largest inland body of water. The water level in the Caspian Sea has changed several times in the past: for instance, it exceeded the current level by more than 50 metres between 13,000 and 18,000 years ago. A number of scientists attribute this phenomenon to a strong influx of water from the melting of the giant Scandinavian Ice Sheet, as well as the flow of liquid from ancient lakes and rivers that no longer flow into the Caspian Sea. This is confirmed by the traces of no longer extant riverbeds discovered on the Russian Plain, which are many times larger than the modern rivers.
The scientists from Lomonosov Moscow State University and a number of specialised institutes of the Russian Academy of Sciences decided to put these hypotheses to the test. Their work was carried out in several areas. First, a group of climatologists and oceanologists modeled the climatic conditions of the Caspian Sea, including its water and thermal regimes, based on the calculations of atmospheric and ocean circulation. The modeling showed that in order to exceed the current water level by 50 metres, the influx of water into the Caspian Sea must be 30–50% stronger than it is today.
Then, a group of paleographers and geomorphologists studied the Russian Plain for the traces of ancient rivers that had carried their waters to the Caspian Sea. By collecting and analysing hundreds of samples, they showed that the age of these riverbeds ranges from 14,000 to 17,500 years, thus coinciding with the abovementioned period of the Khvalynian transgression. The calculated volume of water flow entering the Caspian Sea through these huge channels also turned out to be close to the estimates obtained via modeling.
Finally, hydrologists used a numerical model to reproduce the processes that might have caused this large influx of water into the Caspian Sea. The scientists showed that the chief reason was the widespread distribution of permafrost, which prevented water from being absorbed by soil and evaporating: under these conditions, even a relatively small amount of precipitation could lead to the formation of a river flow whose volume would be 40% higher than today.
“The model calculations and the results of paleogeographic analysis have confirmed the hypothesis that the rise in the level of the ancient Caspian Sea by tens of metres above the current level could have occurred in a cold and relatively dry climate 18,000 to 13,000 years ago, when the contribution of melted glacial waters was either no longer present because the glacier had melted, or was insignificant. Independent estimates obtained by three groups of project implementers have given us similar values: the influx of water into the Caspian Sea was up to one and a half times greater than today, which ensured the maintenance of such a high sea level with little evaporation from its surface. Such an influx in the absence of glacial runoff can be explained by the spread of permafrost on the Russian Plain,” Alexander Gelfan, project leader and doctor of physical and mathematical sciences, is quoted as saying by the Russian Science Foundation.
