???? When the Mediterranean Sea dried up and then suddenly filled

114 K readings / 16 reactions Updated on 18 nov. 2024, 11:37

5.5 million years ago, the Mediterranean Sea lost 70% of its water, covering its bottom with a thick layer of salt. This major upheaval was followed by a cataclysmic filling in just a few months…

When the Mediterranean Sea dried up

Six million years ago, the Mediterranean became isolated from the Atlantic Ocean as seismic movements raised the level of the Strait of Gibraltar, allowing the European and African continent to be connected.

This phenomenon led to the drying of the Mediterranean Sea and a massive accumulation of salt on the seabed, it is the “Messinian salinity crisis“, which took place in the Miocene geological period, between 5.97 and 5.33 million years ago.
It has been known since 1971 when a coring campaign showed that layers of mineral salts, some 3 km thick, line the bottom of the basins and are covered with sediment.

However, it was not until 2007 that the thesis of the isolation of the Mediterranean Sea was accepted by the scientific community. “It is now proven that during the Messinian, continental drift disrupted the Mediterranean ecosystem by closing the straits which supplied water to the Mediterranean Sea.” specifies the Cité des Sciences.

Deprived of its supply of water from the Atlantic Ocean and given the lack of precipitation, the Mediterranean Sea evaporated massively, losing almost a kilometer of water thickness. This drying resulted in the deposition of large quantities of salt on the seabed.
During this period, the average water temperature at 2,000 meters depth was between 35 and 40 degrees!

At the end of 2024, a study led by Giovanni Aloisi, researcher at the CNRS, explained how a million cubic kilometers of salt accumulated on the Mediterranean ocean floor in a brief period, thanks to an analysis of the chlorine isotopes contained in the extracted salts. funds of the Mediterranean.

The analysis of the two stable isotopes of chlorine (³⁷Cl and ³⁵Cl) makes it possible to estimate the rate of salt accumulation and to detect any drop in sea level.

Scientists were thus able to trace the two phases of this extreme drying.

1. In a first phase, around 35,000 years ago, salts were deposited in the eastern part of the Mediterranean due to a partial restriction of its flow towards the Atlantic.
2. During a second, shorter phase (less than 10,000 years), salts accumulated throughout the Mediterranean, causing a rapid drying of the sea, with a drop in water levels of 1. 7 to 2.1 kilometers in the eastern Mediterranean and about 850 meters in its western part. Thus, the Mediterranean basin has lost up to 70% of its water volume.

This spectacular drop in sea level would have had consequences on terrestrial fauna and the Mediterranean landscape. It would also have triggered volcanic eruptions in this region due to the lightening of the earth’s crust, and would have generated climatic effects on a global scale linked to the depression thus created.

The Mediterranean Sea filled in a few months

The fate of the Mediterranean Sea seemed sealed, and yet, following a cataclysmic seismic event similar to the one that isolated it, it filled in just a few months, 5.33 million years ago. ‘years.

Daniel Garcia-Castellanos, physicist from the Jaume Almera Institute of Earth Sciences of the CSIC, developed computer models with his collaborators to simulate this catastrophe: the flow rate of the water that arrived through the Strait of Gibraltar was approximately 100 million cubic meters per hour, a thousand times the flow of the Amazon!

Animation of the Messinian salinity crisis and the filling of the Mediterranean Sea.
Credit : Garcia-Castellanos

The missing data concerned the geological composition of the seabed. An article on the construction of a railway tunnel under the strait gave researchers this information. Indeed, they discovered the existence of an underwater channel 200 kilometers long extending from the west to the east of the strait. The profile of this channel coincides with that of high-flowing rivers and its existence can be explained by erosion caused by a large torrent of water. According to the most plausible hypothesis, what gave rise to this channel was a series of seismic movements which opened the natural dam of the strait in the same way as they had caused its closure 700,000 years earlier.

The Mediterranean Sea is doomed to disappear

Currently, the depth of the Mediterranean Sea at the Strait of Gibraltar is around 900 meters and seems to protect us from a new salinity crisis, at least on a human scale.
However, with continental drift, the Strait of Gibraltar will close in 10 or 20 million years and the Mediterranean Sea will dry up, this time permanently.