Between about 5.97 and 5.33 million years ago the Mediterranean was cut off from the Atlantic in stages and began to evaporate. Salt and gypsum piled up on its floor, rivers cut canyons into its exposed margins, and most of the species found only in that sea died out. This Messinian salinity crisis takes its name from Messina in Sicily. About a million cubic kilometres of salt still lies under the seabed, so nobody doubts that it happened. How far the water fell has been argued over for more than 50 years.
How far the sea fell
Published estimates run from no fall at all to more than 2 000 m. The idea of a nearly empty basin, more than 2 km down, followed the drilling of the 1970s and dominated the literature for decades.
In 2024 a team led by Aloisi measured chlorine isotopes in rock salt from a well in the eastern Mediterranean. They concluded that the level dropped 1.7 to 2.1 km in the east and about 0.85 km in the west. Even so, the deepest eastern basins kept more than 1 km of brine.
A 2022 study led by Gvirtzman argued for much less. It restored the buried Nile canyon to its original shape and put the river’s base level only about 600 m below today’s sea level, which would leave the salt forming under 1 to 3 km of water.
A 2025 model led by García-Castellanos has the level swinging: lakes about 1 795 m below today’s sea level in the west and 1 664 m in the east at the first low point, then an overall rise of more than 1 300 m as erosion let water spill in from the Paratethys lakes to the north. That could explain how the same brackish deposits, known as Lago Mare, turn up both in deep boreholes and along today’s coasts.
Shutting the Atlantic door
The Strait of Gibraltar probably did not yet exist. The Atlantic reached the Mediterranean through two seaways, the Betic corridor, where Spain’s Sierra Nevada now stands, and the Rifian corridor, where the Rif Mountains now stand. Tectonic movement slowly closed them. The Mediterranean loses more water to evaporation than its rivers supply, so without the Atlantic it shrinks.
Gypsum formed first, from 5.97 to 5.60 million years ago. The great fall in level followed between 5.60 and 5.55 million years ago, and Aloisi’s team finds two phases of salt: about 35 000 years in the east only, then under 10 000 years across the whole sea. From 5.55 to 5.33 million years ago the basin held the brackish lakes of the Lago Mare.
Reading the salt
A seismic survey in 1961 found a strong layer 100 to 200 m below the seabed, named the M reflector. In 1970 the drilling ship Glomar Challenger, with Ryan and Hsü as chief scientists, cored it and brought up gypsum, anhydrite, rock salt and, in places, potash. One core held deep-sea ooze that had dried to dust, blown across the hot floor and settled in a brine lake.
The floor was probably very hot. Anhydrite forms only in water above 35 °C, and a 2009 climate model of a fully dry basin gives summers up to 15 °C warmer.
A canyon under Cairo
The Nile’s canyon lies buried beneath its delta and is often compared with the Grand Canyon, which is about 1 857 m deep. Gvirtzman’s team found that 60 km north of Cairo its relief shrinks from 1 500 m as buried to about 1 000 m once the weight of later sediment is taken off, well short of that comparison. In 2026, however, Bosworth and Mitchell used three-dimensional seismic data from south of Cairo to map a canyon 9 km wide with its floor 1 700 to 1 800 m below today’s sea level, cut into hard limestone, and concluded that the eastern sea fell by at least 1 800 m. The same canyon has been read both ways.
What it cost
A 2024 survey of the fossil record led by Agiadi found that only 86 of the 779 species living only in the Mediterranean survived, and that species numbers took at least 1.7 million years to recover. Aloisi’s team argues that a drop of 0.85 km would have linked Africa and Europe through the Betic region and the Balearic Islands, where the goat-like Myotragus later lived in isolation. The crisis ended about 5.33 million years ago with the Zanclean flood.
