Geographically located between the Italian peninsula and Sicily, the Strait of Messina represents the center of the Mediterranean, linking the two adjacent seas, the Ionian and the Tyrrhenian one. Always an area of intense maritime traffic, it has represented a peculiar environment since the time of Greek mythology, as a site of particular hydrographic phenomena, mythologized and attributed to the presence of monsters. In Homer’s day, people talked about two mythical creatures, named Scilla and Cariddi. The longitudinal axis of the Strait of Messina has a total length of 33 km, linking Capo Peloro to Scilla in the north and Capo Scaletta to Punta Pellaro in the south. Its funnel shape opens its narrowest part to the north (3 km), while it enlarges gradually to the south and reaches its maximum width (16 km). With regard to the underwater profile of the Strait, it can be associated to a mountain, whose summit is the «sill» (along the line joining Ganzirri-Punta Pezzo) and whose opposing sides have very different slopes. Into the Tyrrhenian Sea, in fact, the seabed gradually slopes up to 1000 m in the area of Milazzo: one should go beyond Stromboli Island to find the bathymetry of 2000 m. In the southern part (the Ionian Sea), instead, the slope is very steep and it reaches the depth of 500 m between the cities of Messina and Reggio Calabria not far from the «sill», to largely exceed 1200 m just south (Punta Pellaro), reaching 2000 m in the center of an ideal line joining Capo Taormina- Capo d’Armi. The small-scale (3150 m at its narrowest point) is found along the line joining Ganzirri-Punta Pezzo which corresponds to the underwater «sill», with the minimum depth (80/120 m). The Strait of Messina is the point of union/separation between two seas with very different chemical and physical characteristics, such as temperature, salinity and density. The Tyrrhenian Sea is on average colder and less salty than the Ionian Sea, while the upwelling phenomenon along the Sicilian coast between Capo Taormina and Messina, bringing water to the surface, determines that the ionic waters in the Strait are considerably colder than those occurring at the same depth in other areas of the Ionian Sea. In summer, surface water temperatures in the Strait are on average lower than 4-10°C. The currents in the Strait are the result of the dynamic tidal semidiurnal character of the Tyrrhenian and Ionian basins. In fact, they have almost the same tide amplitudes (about 6 hours and a quarter), but out of phase, so to result that the maximum level in the Ionian Sea corresponds to the lowest one in the Tyrrhenian Sea and vice versa. Also, the speed of these currents varies with a rate of about 14 days, going from minimum to maximum values, oscillating from a value of 185 cm/s in a period of syzygies to a minimum of 79 cm/s in quadrature. In fact, the speed can reach values over 200 cm/s if we add other components to tidal motions, such as the action of the wind (drift current) and the difference in density of the Ionian and Tyrrhenian basins water (current gradient). Such high speeds and the huge volumes of water involved (over 750,000 cubic meters per second for a current of 200 cm/s), if compared to the means of navigation in the Homeric times, clearly indicate that the Strait was considered settlement for monsters, able to swallow or wreck boats rapidly. The meeting of two water bodies (Ionian and Tyrrhenian) also determines the onset of a series of phenomena of dynamic instability, created and visible in the well-known spectacular manifestations of turbulence; these «disorders» may arise with the horizontal or vertical development of currents. With regard to vertical development phenomena, they are real eddies formed in specific locations by the meeting of opposing currents and favored by the irregularity of the bottom. The current flowing towards the Tyrrhenian Sea (S > N) is called «montante», while the opposite «scendente». In addition, there is a steady current, with constant direction and a maximum of one node depth which goes with the «scendente» current in the layer between 0- 30 m, while deeper until the bottom the water flows in the opposite direction. At the end of each current phase a short stationary period of «stanca» follows, immediately succeeded by a phenomenon called «taglio», consisting of water bubbling along a strip across the Strait. Subsequently, the waters begin to flow with increasing speed, reaching a maximum value after about three hours, according to the new axial direction. The currents are particularly strong in the following sites: from the beach of Torre Faro up to a mile offshore towards Scilla; from Punta Pezzo up to half a mile offshore towards Scilla; between the lighthouse at Punta S. Raineri and the lighthouse of Punta Secca, where the current reaches the twofold current compared to any other point of the Strait. Because of the complexity of the hydrodynamic phenomena, and since the generated space-time scales are extremely small, it results difficult to easily describe the water bodies in the Strait of Messina. However, simplifying, three types of water masses can be identified: • Waters of Atlantic origin (TSW, Tyrrhenian Surface Water) on average colder and less salty than the Ionian, located in the first 30-50 m of the water column; • Waters of Ionian origin (IW, Ionian Water) on average warmer and saltier and therefore denser than the Atlantic ones, flowing below those of Atlantic origin; • Water named «Mixed» (MMW, Messina Mixed Water) formed by mixing the two different basin waters while crossing the Strait of Messina. Passing of individual water masses with both stationary and oscillatory currents in the Strait of Messina determines the meeting of not immediately miscible waters, due to the difference of physical and chemical characteristics of the two basins, with a loss of identity also far from the central area of maximum turbulence. As a result of periodical abrupt changes of current, from a dynamic point of view, different water masses with strong energy gradients to their boundaries co-exist in the Strait of Messina, causing a high variability of the hydrographic conditions on a small spatial and temporal scale. These conditions have a remarkable effect on the abundance and structure of plankton, benthos and nekton communities. The continuous movement and slow mixing of waters are factors of further quickening of the area. This enrichment condition leads to a stimulating effect on living component, determining the ecosystem biological richness and high biodiversity and emerging from phytoplankton which shows an enrichment in the number of species as those observed in the two basins. As regards zooplankton, we observe significant changes in distribution compared to what occurs in the two adjacent seas. With regard to fish, there are few Mediterranean species that do not belong to the Strait of Messina: some are even exclusive, giving to this area scientifically high importance. The Strait of Messina is a privileged way of communication between the two adjacent basins, and consequently between the eastern and western Mediterranean. In some periods, given its limited scope, fish species of considerable economic interest (swordfish and tuna) and protected species (turtles and cetaceans) are concentrated in both directions across the Strait. The Strait of Messina marine environment, the lagoon system of Capo Peloro and Faro-Ganzirri Lakes and the Sicilian and Calabrian coasts are undoubtedly environmental ecosystems to be protected. The study of biological characteristics of the Strait of Messina waters has, over time, attracted many researchers able to record unusual and particularly attractive natural phenomena. Over the years this environment has been considered «the paradise of zoologists» for its peculiar biological and ecological features.

Lo Stretto di Messina: un ecosistema di upwelling peculiare nel Mediterraneo

MINUTOLI, Roberta;GRANATA, Antonia;
2013-01-01

Abstract

Geographically located between the Italian peninsula and Sicily, the Strait of Messina represents the center of the Mediterranean, linking the two adjacent seas, the Ionian and the Tyrrhenian one. Always an area of intense maritime traffic, it has represented a peculiar environment since the time of Greek mythology, as a site of particular hydrographic phenomena, mythologized and attributed to the presence of monsters. In Homer’s day, people talked about two mythical creatures, named Scilla and Cariddi. The longitudinal axis of the Strait of Messina has a total length of 33 km, linking Capo Peloro to Scilla in the north and Capo Scaletta to Punta Pellaro in the south. Its funnel shape opens its narrowest part to the north (3 km), while it enlarges gradually to the south and reaches its maximum width (16 km). With regard to the underwater profile of the Strait, it can be associated to a mountain, whose summit is the «sill» (along the line joining Ganzirri-Punta Pezzo) and whose opposing sides have very different slopes. Into the Tyrrhenian Sea, in fact, the seabed gradually slopes up to 1000 m in the area of Milazzo: one should go beyond Stromboli Island to find the bathymetry of 2000 m. In the southern part (the Ionian Sea), instead, the slope is very steep and it reaches the depth of 500 m between the cities of Messina and Reggio Calabria not far from the «sill», to largely exceed 1200 m just south (Punta Pellaro), reaching 2000 m in the center of an ideal line joining Capo Taormina- Capo d’Armi. The small-scale (3150 m at its narrowest point) is found along the line joining Ganzirri-Punta Pezzo which corresponds to the underwater «sill», with the minimum depth (80/120 m). The Strait of Messina is the point of union/separation between two seas with very different chemical and physical characteristics, such as temperature, salinity and density. The Tyrrhenian Sea is on average colder and less salty than the Ionian Sea, while the upwelling phenomenon along the Sicilian coast between Capo Taormina and Messina, bringing water to the surface, determines that the ionic waters in the Strait are considerably colder than those occurring at the same depth in other areas of the Ionian Sea. In summer, surface water temperatures in the Strait are on average lower than 4-10°C. The currents in the Strait are the result of the dynamic tidal semidiurnal character of the Tyrrhenian and Ionian basins. In fact, they have almost the same tide amplitudes (about 6 hours and a quarter), but out of phase, so to result that the maximum level in the Ionian Sea corresponds to the lowest one in the Tyrrhenian Sea and vice versa. Also, the speed of these currents varies with a rate of about 14 days, going from minimum to maximum values, oscillating from a value of 185 cm/s in a period of syzygies to a minimum of 79 cm/s in quadrature. In fact, the speed can reach values over 200 cm/s if we add other components to tidal motions, such as the action of the wind (drift current) and the difference in density of the Ionian and Tyrrhenian basins water (current gradient). Such high speeds and the huge volumes of water involved (over 750,000 cubic meters per second for a current of 200 cm/s), if compared to the means of navigation in the Homeric times, clearly indicate that the Strait was considered settlement for monsters, able to swallow or wreck boats rapidly. The meeting of two water bodies (Ionian and Tyrrhenian) also determines the onset of a series of phenomena of dynamic instability, created and visible in the well-known spectacular manifestations of turbulence; these «disorders» may arise with the horizontal or vertical development of currents. With regard to vertical development phenomena, they are real eddies formed in specific locations by the meeting of opposing currents and favored by the irregularity of the bottom. The current flowing towards the Tyrrhenian Sea (S > N) is called «montante», while the opposite «scendente». In addition, there is a steady current, with constant direction and a maximum of one node depth which goes with the «scendente» current in the layer between 0- 30 m, while deeper until the bottom the water flows in the opposite direction. At the end of each current phase a short stationary period of «stanca» follows, immediately succeeded by a phenomenon called «taglio», consisting of water bubbling along a strip across the Strait. Subsequently, the waters begin to flow with increasing speed, reaching a maximum value after about three hours, according to the new axial direction. The currents are particularly strong in the following sites: from the beach of Torre Faro up to a mile offshore towards Scilla; from Punta Pezzo up to half a mile offshore towards Scilla; between the lighthouse at Punta S. Raineri and the lighthouse of Punta Secca, where the current reaches the twofold current compared to any other point of the Strait. Because of the complexity of the hydrodynamic phenomena, and since the generated space-time scales are extremely small, it results difficult to easily describe the water bodies in the Strait of Messina. However, simplifying, three types of water masses can be identified: • Waters of Atlantic origin (TSW, Tyrrhenian Surface Water) on average colder and less salty than the Ionian, located in the first 30-50 m of the water column; • Waters of Ionian origin (IW, Ionian Water) on average warmer and saltier and therefore denser than the Atlantic ones, flowing below those of Atlantic origin; • Water named «Mixed» (MMW, Messina Mixed Water) formed by mixing the two different basin waters while crossing the Strait of Messina. Passing of individual water masses with both stationary and oscillatory currents in the Strait of Messina determines the meeting of not immediately miscible waters, due to the difference of physical and chemical characteristics of the two basins, with a loss of identity also far from the central area of maximum turbulence. As a result of periodical abrupt changes of current, from a dynamic point of view, different water masses with strong energy gradients to their boundaries co-exist in the Strait of Messina, causing a high variability of the hydrographic conditions on a small spatial and temporal scale. These conditions have a remarkable effect on the abundance and structure of plankton, benthos and nekton communities. The continuous movement and slow mixing of waters are factors of further quickening of the area. This enrichment condition leads to a stimulating effect on living component, determining the ecosystem biological richness and high biodiversity and emerging from phytoplankton which shows an enrichment in the number of species as those observed in the two basins. As regards zooplankton, we observe significant changes in distribution compared to what occurs in the two adjacent seas. With regard to fish, there are few Mediterranean species that do not belong to the Strait of Messina: some are even exclusive, giving to this area scientifically high importance. The Strait of Messina is a privileged way of communication between the two adjacent basins, and consequently between the eastern and western Mediterranean. In some periods, given its limited scope, fish species of considerable economic interest (swordfish and tuna) and protected species (turtles and cetaceans) are concentrated in both directions across the Strait. The Strait of Messina marine environment, the lagoon system of Capo Peloro and Faro-Ganzirri Lakes and the Sicilian and Calabrian coasts are undoubtedly environmental ecosystems to be protected. The study of biological characteristics of the Strait of Messina waters has, over time, attracted many researchers able to record unusual and particularly attractive natural phenomena. Over the years this environment has been considered «the paradise of zoologists» for its peculiar biological and ecological features.
2013
9788849525755
File in questo prodotto:
Non ci sono file associati a questo prodotto.
Pubblicazioni consigliate

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11570/2549030
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact