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Date Published: 08/03/2024

The time when Andalucia was floating between Africa and the Iberian Peninsula

Once upon a time, there were several straits between the Mediterranean and the Atlantic, and not just the Strait of Gibraltar

Believe it or not, there was once a time when the south of Spain, including basically all of Andalucía, Murcia and up into Alicante province and Valencia, was an archipelago between the Mediterranean Sea and the Atlantic Ocean.

These days, the place where the Mediterranean and the Atlantic meet is only through the Strait of Gibraltar, but about 8 million years ago there were actually two straits and an archipelago of islands.

On the one hand, there was a southern corridor and another narrow one in what is now the Guadalquivir basin. This was explained by Francisco Javier Rodríguez Tovar, a professor of palaeontology at the University of Granada (UGR).

He has been contributing to a project of the International Ocean Discovery Program, which seeks to understand the tectonic evolution and closure progressive of the Strait of Gibraltar and the impact that this has had on the Mediterranean Sea, on marine circulation with the Atlantic and on the global climate.

To this end, a group of scientists aboard the American ship Joides Resolution participated in Expedition 401 of the Investigating Miocene Mediterranean-Atlantic Gateway Exchange (IMMAGE) project from December 11, 2023, to February 9, 2024, to investigate the evolution of the Strait of Gibraltar and the Subbetic and Riffian Straits starting 8 million years ago.

The scientific mission has brought together 27 scientists from around the world on the oceanographic vessel, and during their two months navigating around these waters, the program carried out a series of deep sea surveys on both sides of the Strait of Gibraltar, one off the coast of Portugal, another off Cádiz and the third in the Alboran Sea, near Marbella.

Furthermore, in the coming years two, more surveys will be carried out in what were the ancient straits and which today are buried by several hundred metres of sediments, one of them in the Guadalquivir basin, west of Seville, and another in northern Morocco.

Both these connections were gradually closed due to the tectonic uplift of the Betic mountain range in Andalucía and the Rif mountain range in Morocco between 5.5 and 6 million years ago.

The Mediterranean Salinity crisis

The water provided annually by the main rivers that flow into the Mediterranean was not enough to compensate for the water lost through evaporation, so the water level then began to drop until it reached about 1,500 metres below the current level. At the same time, salinity increased, reaching salinities higher than those that exist today in the Dead Sea.

This affected the dynamics of life in the area, which experienced an unprecedented crisis. The final result was the deposit of a large layer of salt more than 2 kilometres thick that is today buried by hundreds of metres of sediments and a 3,000-metre layer of water in the deepest part of the Balearic basin, as well as in the Algerian basin and in the eastern Mediterranean, an event that is known as the ‘Mediterranean Salinity Crisis’.

“The objective is to know what happened before, during and after the closure,” says Professor Rodríguez Tobar. This process introduced changes in currents and even in the climate millions of years ago.

The Mediterranean Salinity crisis ended 5.3 million years ago, when the water level in the Atlantic area rose above Gibraltar and suddenly flooded the entire Mediterranean, an event known as the Pliocene Flood.

This July, the scientists participating in the expedition will meet in the German city of Bremen to sample the repository of their surveys. Each of the specialists will carry out their investigation and later there will be a sharing that will launch conclusions about that event.

“It is a long-term study but from the quality of the sediment in the first results it is seen that unprecedented information and many results are going to be obtained,” assures Rodríguez Tovar, who was selected among scientists from all over the world for this project for his contributions to ichnology.

Co-led by doctors Rachel Flecher (University of Bristol, United Kingdom) and Emmanuelle Ducassou (University of Bordeaux, France), the expedition includes experts from more than 15 countries.

Image 1: Romain Pellen, IFREMER – GM-LGS, Francia

Image 2: IODP

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