A recent study led by a CNRS scientist analyzed the significant drop in the Mediterranean Sea level during the monumental geological event known as the Messinian Salinity Crisis. This event, which occurred between 5.97 and 5.33 million years ago, transformed the Mediterranean into a massive salt reservoir. Until recently, the way in which approximately one million cubic kilometers of salt accumulated on the Mediterranean seabed in a short period of time remained unknown.

Thanks to the analysis of chlorine isotopes in the salt deposits from the Mediterranean seabed, researchers identified two stages of this extreme desiccation process. In the first phase, lasting about 35,000 years, salt deposits began to accumulate in the eastern Mediterranean due to a partial restriction in the connection between this sea and the Atlantic Ocean.

Subsequently, in a second, much shorter stage (less than 10,000 years), widespread salt deposits formed throughout the entire Mediterranean, leading to a rapid desiccation of the waters. This caused the water level to drop by 1.7 to 2.1 kilometers in the eastern Mediterranean and approximately 850 meters in the western sector, resulting in a loss of up to 70% of the total water volume in the Mediterranean.

Messinian saline crisis
The two phases of accumulation of the Mediterranean salt layer during the Messinian salinity crisis. In the first phase, salt accumulated in a brine-filled Mediterranean basin; in the second phase, salt accumulated in a Mediterranean completely isolated from the Atlantic Ocean as a result of the significant drop in sea level in the western and eastern Mediterranean sub-basins. Credit: Giovanni Aloisi

The repercussions of this remarkable drop in sea level were not limited to a change in the Mediterranean’s geography. The drastic desiccation affected both the terrestrial ecosystem and the landscape of the entire Mediterranean basin. Additionally, the reduction in weight on the Earth’s crust caused by the disappearance of this massive body of water may have triggered volcanic activity in the region.

This crustal relief not only generated local alterations but also influenced the global climate, as the depression caused by the water loss impacted global climate patterns.

The results provide a fresh perspective on past geological dynamics and the impact of extreme desiccation events on ecosystems and the global climate.

Scientists conclude that, in the final moments of this salinity crisis, the Mediterranean’s level was approximately one kilometer below the Atlantic level, creating such an extreme difference that it eventually led to the collapse of the Strait of Gibraltar.

This event allowed Atlantic waters to return, ending the crisis, restoring normal flow, and transforming the Mediterranean back into an open sea.

SOURCES

CNRS

Aloisi, G., Moneron, J., Guibourdenche, L. et al. Chlorine isotopes constrain a major drawdown of the Mediterranean Sea during the Messinian Salinity Crisis. Nat Commun 15, 9671 (2024). doi.org/10.1038/s41467-024-53781-6

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