Tuesday, August 3

This is how the Paratetis dried up, a lake bigger than the Mediterranean that bathed the heart of Europe | Science

From northern Croatia to well into Turkmenistan. Lake Paratetis, slightly larger than the Mediterranean Sea, covered an area of ​​more than 2.8 million square kilometers in the heart of Europe. This lake was formed 9.75 million years ago, although it began to gradually dry out until it disappeared 7.65 million years ago. It had the capacity for 1.7 million cubic kilometers of water (just over a third of the Mediterranean and more than ten times the current volume of all fresh and salt water lakes) and it is the largest lake ever recorded to date. A study published in the journal Nature tries to explain how the Paratetis dried up and how this change affected the Europe of the time.

Researchers, thanks to palaeographic reconstructions, maps of the sediment layers of specific areas and data from the coastline, have differentiated four key phases in which the loss of water accelerated. In the first stage, which took place between 9.75 million years and 9.6 million years ago, the water level dropped by about 50 meters. At this time, numerous species disappeared, indicating a major biological crisis for aquatic life, according to the report. There is hardly any data on the second setback, since it occurred very close to the time of the first stage. The third major contraction lowered the water level another 100 meters between 9 million years ago and 8.7 million years ago. The last reduction was the most important and caused the water level to drop more than 250 meters. At this point, Lake Paratetis had divided into several minor lakes toxic to animal life. This phase of desertification ended 7.65 million years ago.

This change in the ecosystem of central Europe was not an isolated event. In addition to the significant change in continental vegetation that occurred, experts estimate that it was during this stage that the deserts of the Sahara and the Arabian Peninsula were formed. Dan Palcu, a researcher at the University of Utrecht, the University of Sao Paulo and author of the study, believes that “having a complete picture of what the interior of Europe was like helps us to understand these climate changes much better”.

As with the water, the lake progressively lost its native fauna. Marine mammal expert Pavel Gol’din, from the Schmalhausen Institute of Zoology in Kiev (Ukraine), says in a note that the Paratetis counted among its inhabitants with dolphins and small whales. Of all the species that swam in these waters, the best known is the Cetotherium riabinini, a whale about 3 meters long. “A large part of the animals went extinct before or during the decline stage, but those that survived found themselves in a world rich in nutrients,” says Palcu. “New species and more opportunities were created for other species to form,” the author concludes.

Comparison between a 'Cetotherium riabinini' of about 3 meters versus a human of 1.8 meters in height.
Comparison between a ‘Cetotherium riabinini’ of about 3 meters versus a human of 1.8 meters in height.Pavel Gol’din

But the absence of water also opened up new opportunities for land animals. “The Central Asian fauna was blocked by the lake, but as the lake retreated, corridors were formed for the animals. It was not an exodus, it was something gradual that lasted several generations ”, explains the researcher. The archaeological remains provide more information about the fauna of the moment, according to Isaac Casanovas, researcher at the Catalan Institute of Paleontology. “Around the lake, at times when there was less water, a series of animals evolved that are those that we now associate with the African savannah, such as antelopes or giraffes. They originate in this area and then invade Africa ”, he says. Something similar happened then in the Arabian peninsula, which dried up and pushed its inhabitants to move to Africa.

This lagoon has been studied for more than 100 years although the conclusions reached by scientists did not fit each other. Palcu explains it as a book from which desertification tore off several sheets: “When the lake dried up, erosion removed many of these pages, so we had to find a location that erosion would not have reached,” he comments by mail. “Once we found the complete story, we were able to make sense of the incomplete stories and start to put it all together,” says the expert.

Currently, the only traces of the Paratetis left in our world are the Caspian Sea basin (which is still a lake) and the Black Sea, which is connected to the Mediterranean. The other remaining vestige, the Aral Sea, is about to suffer the same fate as its predecessor, in what Palcu considers “one of the greatest human-caused ecological disasters.” “We should not take it for granted that large inland water bodies are always going to be there,” he says, warning that the Caspian Sea is at risk of retreating further and unleashing a natural catastrophe in the region.

“I think the first thing that can help improve is climate models. But this study can be extremely useful for anthropologists and mammalian specialists ”, says Palcu about the possible applications of the work. Isaac Casanovas focuses on this second application: “Knowing the behavior history of different species, even if they are extinct, allows you to make an analogy and see how they adapted then. You can use the past to predict what will happen and have time to devise a strategy to prevent it. Creating protected areas or making sure to connect the populations of the humid areas that may remain to prevent them from becoming genetically impoverished are two good strategies ”, he summarizes.

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