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

A team led by Giovanni Aloisi, CNRS researcher and geochemist at the IPGP, has highlighted just how significantly the level of 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 ago1. Until now, the process by which a million cubic kilometres of salt accumulated in the Mediterranean basin over such a short period of time remained unknown.

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

Publication date: 18/11/2024

Press, Research

Related themes : Earth System Science

Thanks to analysis of the chlorine isotopes2 contained in salt extracted from the Mediterranean seabed, scientists have been able to identify the two phases of this extreme evaporation event. 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 terrestrial fauna and the Mediterranean landscape – triggering localised 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, published in Nature Communications, provide a better understanding of past extreme geological phenomena, the evolution of the Mediterranean region and successive global repercussions.

Artistic representation of the Gibraltar sill rupture at the end of the Messinian Salinity Crisis. In the final moments of this crisis, the level of the Mediterranean Sea was around 1 km lower than that of the Atlantic Ocean. © Pibernat & Garcia-Castellanos
The two accumulation phases of the Mediterranean salt layer during the Messinian Salinity Crisis. In the first phase, salt accumulated in a Mediterranean Basin filled with brine; 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. © Giovanni Aloisi

Notes

  1. This exceptional event covered the floor of the Mediterranean Sea with a layer of salt up to 3 km thick. Understanding the causes, consequences and environmental changes undergone by the Mediterranean region in response to the Messinian Salinity Crisis is a challenge that has mobilised the scientific community for decades.
  2. Analysis of the two stable chlorine isotopes (³⁷Cl and ³⁵Cl) made it possible to estimate the rate of salt accumulation and detect the drop in sea level.

Ref: G. Aloisi, J. Moneron, L. Guibourdenche, A. Camerlenghi, I. Gavrieli, G. Bardoux, P. Agrinier, R. Ebner et Z. Gvirtzman, Chlorine isotopes constrain a major drawdown of the Mediterranean Sea during the Messinian Salinity Crisis, Nature Communications (2024). DOI : 10.1038/s41467-024-53781-6

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