The movement of tectonic plates and the drop in sea levels once separated the Mediterranean Sea from the Atlantic Ocean, causing water to evaporate and creating a vast saline basin.
Historically, the Mediterranean Sea transformed into a massive saline basin approximately half a million years ago. Evidence of this geological disruption still exists today and similar disasters could potentially occur again in the future, according to IFL Science. This event is known as the Messinian Salinity Crisis. Researchers hypothesize that changes in sea levels prevented the Atlantic Ocean from flowing into the Mediterranean Sea, plunging the region into a near-total desiccation around 5.33 to 5.97 million years ago.
Simulation of the Mediterranean Sea during the Messinian Salinity Crisis. (Photo: Paubahi).
Many scientists believe that the Messinian Salinity Crisis occurred due to the discovery of a thick layer of salt, about 1 kilometer deep, along the seabed of the Mediterranean Sea, first confirmed in the early 1970s. However, not all scholars agree on the nature or scale of the event.
One of the primary causes of the Messinian Salinity Crisis is likely the movement of tectonic plates. The African Plate and the Eurasian Plate slowly collided over thousands of years. Eventually, their slow-moving collision led to the closure of the Strait of Gibraltar, a narrow waterway connecting the Atlantic Ocean and the Mediterranean Sea.
Another factor was the drop in sea levels, which made it more difficult for ocean water to flow through the Strait of Gibraltar. A study in 2015 indicated a global sea level decline around this time was related to the expansion of the Antarctic ice sheet, which retained more water around the southern pole and away from the North Atlantic.
The Mediterranean Sea is particularly susceptible to such changes. Located in a relatively warm and dry region of the planet, seawater evaporates at a very fast rate. Without supplementary water from the Atlantic Ocean, this enclosed sea dried up within just a few thousand years, leaving a salt-covered basin connecting parts of North Africa with southern Europe.
Theoretically, it would have been possible to walk from modern-day Morocco to Spain or from Libya to Italy. In reality, some animals did migrate in such a manner. Several Spanish islands, such as Mallorca, Menorca, Ibiza, and Formentera, were invaded by land-dwelling animals during this desiccation period. Meanwhile, the crisis also devastated the Mediterranean’s marine biodiversity, killing off 89% of the endemic species.
After a long period of separation, tectonic activity again opened the Strait of Gibraltar, allowing a massive influx of Atlantic Ocean water to rush into the Mediterranean Sea. Known as the Zanclean Flood, this was one of the most intense flooding events ever recorded on Earth.
Even today, the Mediterranean Sea remains saltier than the rest of the Atlantic Ocean partly due to the geographic and climatic conditions that contributed to the Messinian Salinity Crisis. Although it is no longer isolated from the Atlantic, the Mediterranean still experiences limited water exchange through the Strait of Gibraltar and suffers from significant evaporation, leading to increased salinity.
It is possible that a similar event may occur again in the future. The Earth’s tectonic plates are constantly shifting, and the Mediterranean region is particularly complex, featuring many unusual fault zones and overlapping tectonic fragments. As the African Plate continues to drift towards the Eurasian Plate, the two may eventually merge to form the supercontinent Afro-Eurasia and eliminate the Mediterranean Sea from the map.
