Study Reveals Mediterranean Lost 70% of Water 5.5 Million Years Ago

The phenomenon occurred between 5.97 and 5.33 million years before Christ, at the end of the Miocene, recall the authors of the study, explaining that the closure of the strait, caused by the movements of the tectonic plates, led to a reduction in the exchange of water between the Mediterranean and the Atlantic Ocean, and consequently, a concentration of salts in the sea. Called the "Messinian salinity crisis", in reference to the Italian city of Messina, this phenomenon affected the bottom of the Mediterranean, which was "covered with a layer of salts up to 2-3 km thick", reaching one million cubic kilometers, explains Giovanni Aloisi, CNRS researcher, geochemist at the Institute of Earth Physics, and director of the study, in a statement to the press.

The significant drop in sea level caused by this episode continues to be the subject of debate. "Some hypotheses said that the level of the Mediterranean had hardly dropped, others that the sea had almost emptied," Aloisi points out. The analysis of the chlorine isotopes contained in the salts extracted from the Mediterranean seabed shows that this crisis took place in two phases. During the first, of about 35,000 years, the Mediterranean was "full of water, as it is now", but the narrowing of the strait "made the exit of salt water towards the Atlantic a little more difficult", which caused an accumulation of salts in its eastern part and made the sea brackish, Aloisi develops.

During the second phase, which lasted about 10,000 years, the strait "completely closed", the Mediterranean "separated" from the Atlantic and the exchanges of water with the ocean were interrupted, adds the researcher, noting that the accumulation of salts led to the drying up of the sea, which lost 70% of its water volume. The situation remained as such until the reopening of the Strait of Gibraltar, notes Aloisi, stressing that this crisis had negative impacts on the landscape and biodiversity of the Mediterranean. "Only microorganisms can live at such high salinity levels," the researcher observes, revealing that the drying up of the sea would have even led to the formation of a land bridge linking Africa and Europe in the western part, which would have allowed "the colonization of the Balearic Islands by mammals", including goats, rodents and rabbits, according to previous studies.

The drop in sea level would also have affected the atmospheric circulation above the Mediterranean basin and caused an increase in volcanic activity in the region. "70% of the volume of the Mediterranean represents an enormous mass of water, which exerts pressure on the lithosphere," details the director of the study.