New study on the formation of the Strait of Bonifacio

A study to be published in September 2020 details the formation of the Strait of Bonifacio after the last glacial maximum. Valuable data to better understand the history of rising sea levels in the sector

The mouths of Bonifacio have not always been this perilous arm of the sea for navigators, subject to the ferocity of the winds and the perfidy of the many rocks scattered all over the place.

About 22,000 years ago, the Strait simply did not exist. We are at the time of the last glacial maximum.

Most of northern Europe is covered in ice and the level of the Mediterranean Sea is 120 to 140 meters below current level. Corsica and Sardinia form a single island of 47,000 m², the largest in the Mediterranean basin.

When did the waters reclaim their rights to this land? “Previously, we thought that the separation between Corsica and Sardinia was relatively recent. We only had modelizations, which were not corroborated ”, explains Matteo Vacchi, doctor of earth sciences at the University of Pisa.

“Our data showed that 10,000 years ago this division already existed. “

This study, conducted by “Data coupling between the southern part of Corsica and the northern part of Sardinia”, will be published in September in the journal Marine Geology, under the very jargonous title of Driving mechanisms of Holocene coastal evolution in the Bonifacio Strait.

It was carried out as part of two collective research programs funded by the Dragon of Corsica and entitled “Geoarchaeological approach to the landscapes of Corsica in the Holocene, between sea and inland” and “Bouches de Bonifacio”.

Research which intends to detail the history of the evolution of the sea level in the Strait of Bonifacio over the Holocene period, that is to say over the last 10,000 years.

“The gradual melting of the northern hemisphere ice caps produced a very rapid rise in sea level, until about 7,000 years ago”, says the study. This elevation “Led to the gradual development of the Strait of Bonifacio”. The sea level in the strait would thus have stabilized 7,000 years ago.

To reach these conclusions, the scientists carried out sediment cores, in other words vertical samples extracted from the ground and several meters long.

They were taken from several sites: islets of the Monks, beaches of Cara Lunga and Piantarella and the island of Cavallo for Corsica.

But also Budelli (an island in the Maddalena archipelago), Capo Testa and Tanca Manna for Sardinia. The samples were then dated at carbon 14.

The Sardinia-Corsica block

The interest of carrying out research in the Strait of Bonifacio lies in particular in the fact that “The Sardinia-Corsica block is considered to be one of the most tectonically stable Mediterranean areas”, according to the study.

All the geographic changes that have occurred in the area over the past 10,000 years can therefore be explained almost exclusively by the climatic factor. “It is an exceptional laboratory for evaluating the interaction between man and the climate! “, s’enthousiasme Matteo Vacchi.

The presence of man in the area has been documented since the Mesolithic (between 9000 and 6000 BC).

“Archaeological evidence of the human presence has been recovered along both sides of the strait and dated from the Mesolithic to Roman times”, thus recalls the document. “The strait was already a natural barrier, but man was able to cross it”, summarizes Matteo Vacchi.

And if for many millennia, the presence of man has had no impact on the morphology of the site, that could soon change.

In a previous study entitled New relative sea-level insights into the isostatic history of the Western Mediterranean, published in 2018 in the journal Quaternary Science Reviews, the researchers worked on the possibility of a post-industrial modification of the level of the Mediterranean.

The research was carried out using data collected in Corsica, Sardinia, Catalonia, the Gulf of Valencia and the Balearics.

“During the last four millennia, the sea level in the western Mediterranean has risen by 0.25 millimeters per year. Over the past 150 years, the level has risen to 1.2 millimeters per year ”, details Matteo Vacchi.

With, ultimately, risks of “Submersion of coastal areas, but also erosion and salinization of coastal plains”.

“It will depend on the measures taken to fight against greenhouse gas emissions”, concludes the researcher.

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