The Messinian salinity crisis: New insights into sea level changes in the Mediterranean

A new study published in Nature Communications, led by Giovanni Aloisi of the Centre National de la Recherche Scientifique - CNRS and the Institut de Physique du Globe de Paris, and carried out by an international team of researchers including Angelo Camerlenghi of the OGS, has shown that the thick layer of salt that lies beneath the Mediterranean seafloor dates back to the Messinian salinity crisis and originated at two different times. The team reached this conclusion by analysing for the first time the stable chlorine isotope composition of rock salt (sodium chloride) and modelling its volumetric precipitation over time.

The Messinian salinity crisis is a geological phenomenon that occurred between 5.97 and 5.33 million years ago. It was characterised by a drastic reduction in the inflow of water from the Atlantic Ocean, which resulted in the Mediterranean transitioning from a sea to a hypersaline basin and then to a lake with either fresh or brackish water. One of the most enduring scientific debates in the field of geoscience concerns the manner in which over one million cubic kilometres of evaporitic rocks (comprising carbonates, gypsum and rock salt) were accumulated during this phase. Some experts posit that the excess of evaporation over the inflow of seawater from the Atlantic Ocean, which caused the deposition of salt, could have led to a reduction in sea level of more than a kilometre. Others, however, suggest that the entire mass of water in the Mediterranean turned into brine, without any significant reduction in sea level.

These findings provide a more comprehensive understanding of the biological, geological and climatic evolution of the Mediterranean. In the western part of the Mediterranean Sea, a reduction in sea level led to the formation of a land bridge between the African and European continents. This bridge was situated in the vicinity of the modern-day southern Iberian Peninsula and Balearic Islands. Such a connection enabled the migration of life forms between the two continents, which subsequently influenced the composition of the vertebrate fauna in the Balearic Islands. Moreover, the reduction in seawater volume and thus in pressure on the litosphere is thought to have caused widespread magmatic upwelling throughout the entire Mediterranean region.