How 70% of the Mediterranean Sea was lost 5.5 million years ago

The Mediterranean Sea dropped during the Messinian Salinity Crisis—a major geological event that transformed the Mediterranean into a gigantic salt basin between 5.97 and 5.33 million years ago.

Until now, the process by which a million cubic kilometers of salt accumulated in the Mediterranean basin over such a short period of time remained unknown. Thanks to analysis of the chlorine isotopes contained in salt extracted from the Mediterranean seabed, scientists have been able to identify the two phases of this extreme evaporation event.

The results are published in Nature Communications.

During the first phase, lasting approximately 35 thousand years, salt deposition occurred only in the eastern Mediterranean, triggered by the restriction of Mediterranean outflow to the Atlantic, in an otherwise brine-filled Mediterranean basin.

During the second phase, salt accumulation occurred across the entire Mediterranean, driven by a rapid (< 10 thousand years) evaporative drawdown event during which sea-level dropped 1.7–2.1 km and ~0.85 km in the eastern and western Mediterranean, respectively. As a result, the Mediterranean Basin lost up to 70% of its water volume.

This spectacular fall in sea level is thought to have had consequences for both the terrestrial fauna and the Mediterranean landscape—triggering localized volcanic eruptions due to unloading of Earth’s crust, as well as generating global climatic effects due to the huge depression caused by the sea-level drawdown.

These results provide a better understanding of past extreme geological phenomena, the evolution of the Mediterranean region and successive global repercussions.