The Mediterranean

The Physical Environment

Geology/geomorphology

The western Mediterranean developed as a result of the convergence of tectonic plates. The Liguro-Provençal Basin opened up as a result of the rotation of the Corso-Sardinian Block. The morphology of the Sanctuary thus includes island areas.

The seabed of the Sanctuary was formed gradually as a result of large-scale folds and thrust faults in the Alpine orogeny, subsidence phenomena that occurred because of extensions in the Neogene period, the morphogenesis of sea-level oscillations in the Quaternary period, atmospheric, marine and fluvial erosion and recent and on-going sedimentation.

These different geomorphological phenomena explain the existence of mountainous areas, plains that extend into rocky coastlines of varying steepness and low coastal sections, often accompanied by lagoons and wetlands. Apart from the plains on the eastern side of Corsica and the Tuscan coast, the coastlines that run along the perimeter of the Sanctuary are rocky and often very steep. Most of the water regimes are torrential, consisting of steep and often interdependent catchment areas. The mouths of the rivers are generally small, with stony sediments.

Underwater topography

The Sanctuary area is characterized by markedly heterogeneous topography and hydrodynamic diversity.

The Liguro-Provençal Basin and the area adjacent to it alongside Corsica and across the Sea of Sardinia lie on a continental platform with a very small border that lies between 2.5 and 10 nautical miles from the coast.

Deep underwater canyons run along paleofluvial channels and tectonic fractures at a depth of over 2000 m in places.

The continental shelf broadens from west to east and is very steep in the Provence region and along Corsica’s western coast, becoming wider in the eastern section and extending as far as 25 km from the Tuscany coasts.

The deepest seabeds are located to the east of the meridian, 5°30' E, and can reach 2,700 m. The northern Tyrrhenian Sea is less deep (reaching a maximum depth of around 1,700 m). It is separated from the Ligurian Sea by the Strait of Bonifacio and the Gulf of Follonica - island of Elba. Its large continental shelf, from which isolated underwater elevations arise, links the two parts.

Climate

The climate of the Sanctuary area is Mediterranean, with hot, dry summers – a result of the Azores High – mild, relatively rainy winters. Local winds vary in direction and intensity, reaching a peak in winter: the Liguro-Provençal Basin is affected by the mistral and tramontane from the N-NW, the northern Tyrrhenian Sea by N-NE winds and the sirocco from the S-SE, and the east coast of Corsica is impacted, to a lesser degree, by the libeccio from the S-SO.

 

Hydrology and Currentology

The water balance of the Mediterranean is negative: high levels of evaporation are not offset by precipitation and water supplied by catchment areas. This negative balance is therefore partly offset by the inflow of Atlantic waters that is higher than the outflow of Mediterranean waters.

The Mediterranean’s northwestern water masses circulate along the continental slope in a cyclonic circuit induced by the density gradients of three different water zones:

  • a surface zone up to 300-400 m deep, composed of Atlantic waters and additional freshwater from rain and rivers,
  • an intermediate zone between 200 and 500 m deep, which is denser, richer in nutrients and relatively warm,
  • more homogenous deep water, with a near-constant annual temperature of 12.7°C. Wind-induced water exchanges are more intense in winter when subsurface waters rise to the surface in upwellings.

The intermediate waters also form part of this current. They flow into the Tyrrhenian Sea and divide in order to cross the Canal of Corsica, passing west beyond Sardinia and Corsica. By the Cap Corse, there is a second current from the eastern Mediterranean. The two currents meet to the north of Corsica, forming the Liguro-Provençal current that flows up to the north towards the Gulf of Genoa before turning to the west along the coast towards Spain. As a result of cyclonic flow, the current gives the Liguro-Provençal Basin its dome-shaped point of divergence and frontal zone structures, which are both significant in terms of their biological productivity.

The intermediate waters also form part of this current. They flow into the Tyrrhenian Sea and divide in order to cross the Canal of Corsica, passing west beyond Sardinia and Corsica. By the Cap Corse, there is a second current from the eastern Mediterranean. The two currents meet to the north of Corsica, forming the Liguro-Provençal current that flows up to the north towards the Gulf of Genoa before turning to the west along the coast towards Spain. As a result of cyclonic flow, the current gives the Liguro-Provençal Basin its dome-shaped point of divergence and frontal zone structures, which are both significant in terms of their biological productivity.

Oceanographic processes and structures

For management purposes, different categories of zones were identified:

  • static bathymetry (canyons),
  • stable hydrographic phenomena,
  • ephemeral and mobile hydrographic phenomena (upwellings, frontal systems).

Biological productivity is high, particularly in areas where there is upwelling and in frontal zones, where plankton-eating marine mammals congregate.

The Sanctuary is also home to a large number of the different marine and coastal habitats of the Mediterranean. Numerous studies have sought to distinguish cetaceans’ habitats by classifying the temperature of surface waters in which different species live, and the different water masses present, depths and topographic structure, hydrological phenomena including upwellings and fronts or the combination of multiple spatial-temporal factors. According to such findings, preferred habitats seem to be the continental shelf and pelagic zone; the presence of marine mammals is often determined by the distribution of the prey they feed on.