Mediterranean Sea

The Mediterranean Sea, located between southern Europe and North Africa, is one of the most historically important and largest seas in the world. However, environmental problems caused by tourism, industrial discharge, and climate change threaten to destroy the ecological balance of the region.

Location and History

The Mediterranean Sea separates Africa geographically from the continents of Europe and Asia. It is surrounded by southern Europe, western Asia, and North Africa and extends about 3,700 kilometers (1,429 miles) from east to west and almost 1,600 kilometers (994 miles) from north to south at its widest point. Because of the irregular shoreline, the width varies considerably but averages almost 600 kilometers (373 miles). The European coast includes Spain, France, Italy, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania, Greece, the islands of Malta and Cyprus, and the European part of Turkey. The Asian portion continues with the Asian part of Turkey, Syria, Lebanon, and Israel, while the African part includes Egypt, Libya, Tunisia, Algeria, and Morocco. Its total area is about 2.5 million square kilometers (965,265 square miles).

The Mediterranean Sea is connected to the Atlantic Ocean by the Strait of Gibraltar in the west, to the Red Sea by the Suez Canal in the southeast, and to the Black Sea by the Strait of Bosporus in the northeast. The Strait of Gibraltar is approximately 20 kilometers (12 miles) wide at the boundary, while the Bosporus varies in width from as little as 0.8 kilometer (1/2 a mile) to about 3.2 kilometers (2 miles) at the Black Sea boundary between Rumeli Burnu in European Turkey and Anadolu Burnu in Asiatic Turkey. The Suez Canal is the only human-made channel of the three and was first opened in the late 1860s to speed naval transportation between Europe and the countries of the Persian Gulf and the Indian Ocean. It is almost 150 kilometers (93 miles) long, 82 meters (269 feet) wide, and about 10 meters (33 feet) deep.

Historically, the Mediterranean Sea has been one of the most important as well as one of the largest seas on Earth. Its name is derived from the Latin words medius (middle) and terra (land), indicating its perceived identity to ancient cultures as the “sea in the middle of the world.” The Mediterranean area has also been known as “the cradle of Western civilization” because of the advanced civilizations, from ancient to present-day, that flourished in the region.

All three straits and canals have long been considered critical strategic points for commercial, political, naval, and military reasons, and great military powers have, historically, been interested in controlling them. Such powers included the Phoenicians, the Greeks, the Romans, the Persians, the Byzantines, the Arabs, the Turks, the British, the French, the Italians, the Russians, and others. The Romans referred to the Mediterranean as mare nostrum (our sea); Catherine the Great of Russia had dreams about controlling the Dardanelles in the late 1790s; British admiral Horatio Nelson understood that blocking Gibraltar was the only way to beat Napoleon’s expansion; Winston Churchill realized that controlling the Dardanelles was critical during World War II; Benito Mussolini attempted to control the Balkan Peninsula and North Africa to revive the ancient Roman Empire; and the British and French declared war against Egyptian President Gamal Abdel Nasser after he nationalized the Suez Canal.

Geography

The present coastline of the Mediterranean is irregular and indented with numerous small gulfs and capes. Geological studies indicate that during the Triassic period, some 200 million years ago, a sea known as Tethys Sea extended as far east as Turkmenistan and the Aral Sea territory and as far north as what is now the Danube Valley in central Europe. The area north of the Tethys Sea was called Laurasia, while the area south of it was known as Gondwanaland. That much larger and wider body of water is believed to have been contracted by tectonic factors such as faulting, folding, continental drift, and volcanism as the continental masses moved from their orientation in the supercontinent of Pangaea toward their present global distribution. Beginning in the Cretaceous era (65 million years ago) and ending during the Miocene period (13 million years ago), the smaller Aral, Caspian, Black, Marmara, and Mediterranean seas were created out of that much larger sea basin. Moreover, the two natural outlets of Gibraltar and the Dardanelles appear actually to have been completely landlocked by land bridges that were eventually worn off by the tides, allowing the waters of the outer ocean to inundate the Mediterranean basin. There is also an indication that the islands situated off the eastern Greek mainland were once attached to what is now mainland Greece and Turkey.

The Italian peninsula splits the Mediterranean into two basins of approximately equal size, the western and the eastern, which are connected by the Strait of Sicily and the Strait of Messina. The Strait of Sicily, which lies between Cap Bon in Tunisia and the Italian island of Sicily, is almost 130 kilometers (81 miles) wide, while the Strait of Messina, which lies between Punta Sottile in Sicily and the Italian mainland, is no more than 3.3 kilometers (2 miles) across.

Each of the two basins is also subdivided into four smaller bodies of water. The western basin is composed of the Alboran Sea to the south of Spain, the Balearic or Iberian Sea between mainland Spain and the Islas Baleares, the Ligurian Sea just north of the French island of Corsica, and the Tyrrhenian Sea, which is surrounded by Corsica, Sardinia, Sicily, and the western part of mainland Italy. The eastern basin includes the Adriatic Sea, which lies between the western parts of some of the former territories of Yugoslavia and the eastern part of mainland Italy all the way down to Capo Santa Maria di Leuca and above the Greek island of Corfu. The Ionian Sea extends southward from the Adriatic Sea, to the east of Sicily and on the western shore of Greece. The Aegean Sea stretches over the eastern Greek shores as far north as the Dardanelles; the Sea of Marmara connects to the Aegean Sea by the Dardanelles and to the Black Sea by the Bosporus Strait.

The Mediterranean has many islands, several of which are of volcanic origin. Most of them lie in the eastern basin of the Adriatic Sea and, in particular, the Aegean Sea. The Aegean has more than two thousand islands that form small basins and narrow passages with an irregular coastline and topography. The largest islands are Sicily, with an area of 25,818 square kilometers (9,968 square miles); Sardinia, with an area of 24,138 square kilometers (9,320 square miles); Cyprus, with an area of 9,282 square kilometers (3,584 square miles); Corsica, with an area of 8,762 square kilometers (3,383 square miles); and the Greek island of Crete, with an area of 8,424 square kilometers (3,253 square miles). Other significant islands in the western basin include Alboran Island and the Balearic islands (Menorca, Mallorca, Ibiza, and Formentera) near Spain, and Elba, the Pontine islands, Ischia, Capri, Stromboli, and the Lipari islands near Italy. In the eastern basin are Malta, off the coast of Tunisia, as well as the Greek Ionian, Cyclades, and Aegean islands. The floor of the Mediterranean is generally made up of carbonate-rich yellow mud, which covers the blue mud floor.

Among the most important rivers that flow into the Mediterranean are the Spanish Ebro, the French Rhone-Saone-Durance, and the Italian Arno, Tiber, and Volturno. Others include the Po and the Tagliamento in Italy, the Vardar in Greece and Macedonia, and the Nestos in Bulgaria and Greece. North Africa has only the Nile, which is the only large river that flows toward the north. Over the years, several deltas have slowly formed at the mouths of the rivers that flow into the sea. The most important one is the Nile Delta, which is the most fertile land in Egypt. More than five thousand years ago, Memphis, the Pharaonic capital of Egypt located close to the current capital, Cairo, was a port.

The coastline is often covered with small hills, while the high-altitude mountains lie farther inland. The presence of volcanoes such as Vesuvius and Etna in Italy has been responsible for the loss of thousands of lives over the years but has also contributed to the fertility of the neighboring land.

Water Flow

The total water area of the Mediterranean is about 2.5 million square kilometers (965,265 square miles), with an average depth of about 1,500 meters (4,921 feet). Generally, the eastern basin is deeper, with the greatest depth of about 5,450 meters (17,881 feet) in the Ionian Sea, approximately 57 meters (187 feet) off the Greek mainland. The western basin’s deepest spot lies in the Tyrrhenian Sea at about 3,600 meters (11,811 feet). The sill depth in both the straits of Sicily and Gibraltar is about 275 meters (902 feet). The Adriatic Sea is the shallowest of all seas because it is an overextension of the continental shelf. The water of the western basin is a little cooler and fresher than that of the eastern basin. The average surface temperature in the west is as low as 11 degrees Celsius (52 degrees Fahrenheit) in February and as high as 23 degrees Celsius (74 degrees Fahrenheit) in August. The corresponding temperatures in the eastern basin are 16 degrees (61 degrees Fahrenheit) and 26 degrees Celsius (79 degrees Fahrenheit). Dissolved salts increase the density of seawater. Seas that are isolated and have few rivers flowing into them are traditionally saltier. This effect is particularly enhanced by arid climates, where the evaporation of surface water is greater than its replenishment by precipitation.

The Mediterranean, which fulfills all these requirements, has a sill at the entrance of Gibraltar. As a result, water from the lower-density but colder Atlantic Ocean flows in at the surface. At the same time, the Mediterranean water flows over the sill into the ocean, where it sinks to a much lower depth until it reaches levels of the same density. Although a considerable degree of mixing takes place at the upper level because of the initial flow of salty water to the Atlantic, once the water reaches the high-density region, it spreads horizontally and can be followed far into the Atlantic. In general, however, the deep outflowing current does not equal the intake of surface water. The measurement and comparison of salinities of the Atlantic and Mediterranean waters in the Strait of Gibraltar provide data that give an accurate measurement of the outflow of water. Taking into consideration also the evaporation rates, the outflow has been estimated to be in the neighborhood of 35 to 63 million cubic feet (991,090 to 1,783,961 cubic meters) per second. Temperature and wind variability have an impact on the actual outflow.

Generally, the salinity of the western Mediterranean basin is less than that of the eastern basin. The water mass flowing from the Black Sea through the Bosporus and the Dardanelles to the north of the Aegean Sea is estimated to be close to 200 cubic kilometers (48 cubic miles) per year. The Dardanelles boundary condition results in the spreading of the outflow to the Western Aegean, as well as to the north, along the Greek mainland coast. Black Sea waters appear to be able to reach the central Aegean; their influence is greatest in summer and fall during the time of maximum discharge through the Dardanelles in September and minimum salinity in July. Moreover, a westerly current enters the area between Asia Minor and the Greek island of Rhodes, which reverses in spring and summer. Along the northern coast of Crete, easterly currents appear to move all year long. The tide that is attributed to the Atlantic Ocean appears to lose strength in the Strait of Gibraltar.

The Mediterranean tides are generally semidiurnal, with wave systems that have nodal lines that extend from Barcelona, Spain, to Bejaia, Algeria, and from Turkish Korfezi to Libyan Tobruk. The tide range in most other places does not surpass the 1-meter (3.3-foot) mark. Strong hydraulic currents occur at the ends of the two straits of Sicily and Messina because of the formation of high water in exactly opposite phases. These are the same waves that made the Messina Strait such a dangerous place to navigate in ancient times—this area was known as Scylla and Charybdis in Homer’s Odyssey. In contrast, the Adriatic has a progressive tide that has the highest range of 1 meter (3.3 feet).

Historically, the study of currents was investigated because of the observed continuous inflow of water through the Strait of Gibraltar. Scientists became aware of the fact that the evaporation of water over the Mediterranean was larger than the precipitation and river water outpouring. As a result, the possibility of underground canals that would bring back the water to the Atlantic was theorized. It is estimated that Gibraltar provides more than 97 percent of the water entering the Mediterranean, while precipitation, the Black Sea, and river flow provide the rest. In contrast, of the water lost by the Mediterranean, 93 percent leaves through Gibraltar, more than 6 percent is evaporated, and less than 0.5 percent is lost to the Black Sea. There is no doubt that if the Atlantic water inflow through Gibraltar did not occur, the Mediterranean Sea would be a large, salty pond supporting little or no life, similar to the Dead Sea.

Climate and Plant Life

The Mediterranean climate is transitional between the harsh weather of central Europe and the desert-dominated conditions found in North Africa. Because of the decreased humidity, the overall climate is comfortable for its inhabitants. A small degree of sleet and snow precipitation takes place, especially in the mountains, and is supported by occasional polar or Arctic invasions of cold winds. However, the monthly temperature averages never drop below freezing, which is particularly favorable to crops. The southern parts of North Africa and the eastern basin, which are closer to the equator, experience hotter and drier summers because they lie far from the Atlantic Ocean’s influence.

Overall, the eastern basin is roughly 6 degrees of latitude nearer to the equator than the western basin. In particular, the Sahara Desert in North Africa makes the greatest parts of Egypt, Libya, and Algeria practically uninhabitable. Often there are three- to four-month spans where no precipitation occurs in the eastern basin, while the western basin territory experiences numerous storms and substantial amounts of rains.

In general, the term “Mediterranean climate” refers to a long, hot, dry summer and a short, cool, wet winter. Several locations on Earth experience the same conditions, such as Los Angeles in California, Santiago in Chile, Capetown in South Africa, and several cities in southwestern Australia. The mild, dry summers and the beautiful scenery of many areas in the Mediterranean prompt a great number of tourists to visit the beaches of the French and Italian Rivieras, southern Italy, the Adriatic coast, the coasts of Lebanon, and the islands of Greece. The unique climate supports characteristic crops and vegetation. The dry weather favors the growing of the long-rooted olive trees and oaks, as well as the dominance of the dense scrub 2 to 4 meters in height known as maquis in France and macchia in Italy. All lose very little water by evaporation and have a thick bark and small, thin leaves. Interestingly, the climate helps to grow fruit that is characteristic of several other places on Earth, such as grapes and oranges, as long as there is enough water during the dry season.

Significance

The Mediterranean Sea’s impact on civilization has also added to problems that the human race is encountering. The ecosystem has been substantially eroded by the destruction of forests, which has been taking place for more than thirty centuries. The Phoenicians, Athenians, Romans, Byzantines, and Turks were significant naval powers and used timber for ship construction. The citizens of Athens, Rome, Jerusalem, Alexandria, and Constantinople routinely consumed large numbers of trees in the building of their cities.

Tourism and industry are responsible for one of the greatest concerns, pollution. The use of iron, steel, concrete, petrochemicals, and other industrial products has affected the air quality of cities such as Rome, Athens, Marseilles, and Barcelona. The presence of millions of tourists has led to the need for more sanitary facilities and for recycling projects. Often the natives encounter the great problem of raw sewage and other refuse that overwhelms the beaches.

Furthermore, oil spills have also added to environmental pollution. The 1975 United Nations-sponsored Mediterranean Action Plan (MAP) convinced most Mediterranean nations to sign a pact to eliminate toxic spillage and chemical waste from the Mediterranean. In 1982, the MAP Coordinating Unit was established in Athens, followed in 1995 by the adoption of MAP Phase I, Barcelona Resolution, Priority Fields of Activities for Environment and Development in the Mediterranean Basin (1996–2005) and the Protocol Concerning Specially Protected Areas and Biological Diversity in the Mediterranean. Beginning in 2014, the Horizon 2020 initiative aimed to depollute the Mediterranean Sea by 2020, targeting industrial emissions and municipal and urban waste waters, which made up 80 percent of pollutants entering the sea. In a continuing effort, the Horizon 2020 program was expanded into the Horizon Europe initiative, which set new targets for 2027. In 2017, several European environmental organizations created an initiative to designate the Mediterranean Sea as an Emission Control Area (ECA), which would limit the air pollution produced by ships. An impact assessment investigation performed by France, released in 2018, revealed that implementation of the ECA could reduce up to 20 percent of particulate matter and reduce nitrogen dioxide levels by up to 76 percent. This program was also expanded in 2022 to further designate the Mediterranean as a Sulphur Emissions Control Area (SECA) dedicated to the reduction of sulfur emissions used in fuel oil by 2025.

In early 2019, the Mediterranean Sea drew public attention as the path taken by thousands of immigrants fleeing from Northern Africa to Europe. After a boat crossing the Mediterranean filled with over one hundred migrants capsized in January 2019, news outlets labeled it one of the world's deadliest sea crossings. In 2022, over two thousand migrants were reported to have drowned or gone missing while crossing the Mediterranean Sea, though the number is certainly much higher.

Climate change is also impacting the water temperatures of the Mediterranean Sea. The entire Mediterranean region is warming 20 percent faster than the global average. Rising temperatures are changing marine life, and some tropical species from the Atlantic Ocean have colonized parts of the Mediterranean. Many native species have been in a degraded state due to rising temperatures. Agencies and non-profits such as the United Nations Environment Program and the Coordinating Unit for the Mediterranean Action Plan have been monitoring changes throughout the twenty-first century and implementing various plans in order to save wildlife and protect water while continuing to serve the public.

Principal Terms

continental shelf: the submerged offshore portion of a continent, ending where water depths increase rapidly from a few hundred to thousands of meters

eddy: a smaller, rotating current or turbulence that forms from the movement of a primary water or wind current

Mediterranean climate: a pattern of weather conditions characterized by a long, hot, dry summer and a short, cool, wet winter

salinity: a measure of dissolved salt content in oceanic water controlled by the difference between evaporation and precipitation and by the water discharged by rivers

semidiurnal: having two high tides and two low tides each lunar day

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