Cienciaes.com: The currents of the Mediterranean in the last 14,000 years. We spoke with Sergi Trias Navarro.

2023-05-22 15:34:46

Through a strait barely 15 kilometers wide, the Strait of Gibraltar, the waters of the Atlantic Ocean enter those of the Mediterranean Sea. At that point, which separates Europe from Africa, the Atlantic waters begin a path that runs the more than 3,800 kilometers that separate it from the Asian coasts of Turkey, Lebanon or Israel, in what is known as the Levantine Sea. In the middle is the Strait of Sicily, a place that forms a shallow barrier between two very deep basins, the western one, located in the Gulf of Leon, and the eastern one formed by the Aegean and Levantine seas. On their way back, after passing the Strait of Sicily, the waters return to the Atlantic and the cycle is completed. This exchange of water between the ocean and the sea has been going on since ancient times, although, as our guest, Sergi Trías Navarro, tells us today, it undergoes variations, variations that are reflected in the sediments accumulated at the bottom of the Mediterranean waters. . The researchers collect samples of sediments from the seabed and analyze them, layer by layer, like the pages of a history book, the history that connects the Mediterranean Sea with the Earth’s climate.

At the end of the last ice age, a very humid and rainy period began, which notably increased the supply of fresh water to the Mediterranean from the rivers of North Africa. That period, known as the African Humid Period, spans from 15,000 to 6,000 years before present time. But it was not a uniform period, it suffered great variations at times. The most important occurred between 12,900 and 11,700 years, during a period known as the Younger Dryas or Joven Dryas. At that time there was a drastic reversal and the climate became colder and more arid, an imitation of the rigors of the ice age. The change in climatic conditions influenced the exchange of waters in the Mediterranean and has been the subject of research, the results of which have recently been published in an article in the journal Communications of Earth and Environment, first signed by Sergio Trías Navarro, Marine Geosciences researcher in the Department of Earth and Ocean Dynamics of the Faculty of Earth Sciences at the University of Barcelona.

An essential characteristic of the Mediterranean Sea is that more water evaporates than it receives from the rivers that flow into it. As a consequence of this deficit, the Mediterranean thermohaline circulation system, that is, the current that runs through it driven by changes in temperature and density, receives more water from the Atlantic than it pours into it.

The fresh and cold Atlantic surface waters that enter through the Strait of Gibraltar are progressively transformed into saltier surface waters, which sink to intermediate depths in the Levantine Sea, located in the easternmost extreme along the Asian coasts. Subsequently the waters sink further and form the Eastern Mediterranean Deep Water, all these layers of water flow together through the Strait of Sicily to the west, contributing to the deep water convection in the Gulf of Lion and flow back into the Gulf of Lions. Atlantic Ocean through the Strait of Gibraltar.

The Strait of Sicily is shallower than the eastern and western basins of the Mediterranean and becomes a kind of barrier that the different currents must overcome. It is, for this reason, a place where the water exchange between the eastern and western sides of the Mediterranean is very sensitive to changes in climatic conditions.

Sergio Trías and his group of researchers have extracted samples from the sediments of the Strait of Sicily and other regions of the Mediterranean and have studied the traces left by the changes in the different currents that have passed through it over the last 14,000 years. The results indicate a higher outflow from the eastern Mediterranean during the Younger Dryas, twice as high as the current outflow.

I invite you to listen to Sergio Trías Navarro, a Marine Geosciences researcher in the Department of Earth and Ocean Dynamics of the Faculty of Earth Sciences at the University of Barcelona.

References:

Trias-Navarro, S., Pena, L.D., de la Fuente, M. et al. Eastern Mediterranean water outflow during the Younger Dryas was twice that of the present day. Commun Earth Environ 4, 147 (2023).