Scientists think they now know how the Mediterranean almost dried up millions of years ago

Messinian Salinity Crisis led to build-up of salt almost three miles thick under the seabed

Researchers have published a theory as to how the Mediterranean basin once lost up to 70 per cent of its water volume. AP

Scientists believe they have solved the mystery of how the Mediterranean Sea almost dried up millions of years ago, leading to the build-up of a layer of salt up to nearly 5km thick under the basin.

A study into how the massive amount of salt was deposited during the extreme evaporation, which researchers call the Messinian Salinity Crisis, shows it happened in two phases.

In the first, the sea became cut off from the global ocean, leading to salt deposits in the eastern Mediterranean, it said. Previous studies have suggested that happened when the precursor to the Strait of Gibraltar closed almost six million years ago due to the movement of Earth’s tectonic plates, which also led to waterways connecting Spain and Morocco to the Atlantic being shut off.

During the second phase, according to research published in Nature Communications, salt built up across the entire Mediterranean, driven by a rapid drop in sea level of between 1.7km and 2.1km in its eastern arm, and about 0.85km in the eastern part.

As a result, the Mediterranean basin lost up to 70 per cent of its water volume, the study found, leaving the sea level an average of 1km lower than the Atlantic Ocean.

Scientists believe that helped trigger nearby volcanic eruptions due to unloading of Earth's crust, as well as generating global climatic effects due to the huge depression caused by the falling sea level.

Researchers say the results provide a better understanding of ancient extreme geological phenomena, the evolution of the Mediterranean region and successive global repercussions.

The Messinian Salinity Crisis ended about 5.33 million years ago, with an event known as the Zanclean flood or Zanclean deluge, which reconnected the Mediterranean to the Atlantic.

Scientists believe it may have been the largest flood in the planet’s history, about 1,000 times larger than the flow of the Amazon river, according to some estimates. One model suggests 90 per cent of the flooding of the Mediterranean took place over a period lasting up to two years.

According to the UN Environment Programme, the Mediterranean is warming at a rate 20 per cent faster than the global average.

The air temperatures in the region have already increased by an average of 1.54°C compared to pre-industrial levels, and by 2040 are forecast to have risen a total of 2.2°C. Seawater is about 0.4°C warmer.

Research has indicated significant loss of marine species in the eastern Mediterranean because of climate change.

A study in 2021 found that in some sea habitats off Israel, for example, the number of native species had been reduced by up to 95 per cent. In other habitats, including intertidal areas, described as “more tolerant to climate extremes”, about 50 per cent of the original species diversity remained.