Mediterranean Sea

Greek (red) and Phoenician (yellow) colonies in antiquity c. the 6th century BC

The Roman Empire at its farthest extent in AD 117

Some of the world's greatest ancient civilizations that were the base of the entire Western culture were located around the Mediterranean shores and were greatly influenced by their proximity to the sea. It provided routes for trade, colonization, and war, as well as food (from fishing and the gathering of other seafood) for numerous communities throughout the ages.[5]

Due to the shared climate, geology, and access to the sea, cultures centered on the Mediterranean tended to have some extent of intertwined culture and history.

The most notable Mediterranean civilizations in classical antiquity were the Greek city states, Persians and the Phoenicians, both of which extensively colonized the coastlines of the Mediterranean. Later, when Augustus founded the Roman Empire, the Romans referred to the Mediterranean as Mare Nostrum ("Our Sea"). For the next 400 years, the Roman Empire completely controlled the Mediterranean Sea and virtually all its coastal regions from Gibraltar to the Levant.

Darius I of Persia, who conquered Ancient Egypt, built a canal linking the Mediterranean to the Red Sea. Darius's canal was wide enough for two triremes to pass each other with oars extended, and required four days to traverse.[6]

In 2019, the archaeological team of experts from Underwater Research Center of the Akdeniz University (UA) revealed a shipwreck dating back 3,600 years in the Mediterranean Sea in Turkey. 1.5 tons of copper ingots found in the ship were used to estimate its age. The Governor of Antalya Munir Karaloğlu described this valuable discovery as the "Göbeklitepe of the underwater world”. It has been confirmed that the shipwreck, dating back to 1600 BC, is older than the "Uluburun Shipwreck" dating back to 1400 BC.[7][8][9]

The Western Roman Empire collapsed around 476 AD. Temporarily the east was again dominant as Roman power lived on in the Byzantine Empire formed in the 4th century from the eastern half of the Roman Empire. Another power arose in the 7th century, and with it the religion of Islam, which soon swept across from the east; at its greatest extent, the Arabs, under the Umayyads, controlled most of the Mediterranean region and left a lasting footprint on its eastern and southern shores.

The Arab invasions disrupted the trade relations between Western and Eastern Europe while disrupting trade routes with Eastern Asian Empires. This, however, had the indirect effect of promoting the trade across the Caspian Sea. The export of grains from Egypt was re-routed towards the Eastern world. Products from East Asian empires, like silk and spices, were carried from Egypt to ports like Venice and Constantinople by sailors and Jewish merchants. The Viking raids further disrupted the trade in western Europe and brought it to a halt. However, the Norsemen developed the trade from Norway to the White Sea, while also trading in luxury goods from Spain and the Mediterranean. The Byzantines in the mid-8th century retook control of the area around the north-eastern part of the Mediterranean. Venetian ships from the 9th century armed themselves to counter the harassment by Arabs while concentrating trade of Asian goods in Venice.[10]

The Battle of Lepanto, 1571, ended in victory for the European Holy League against the Ottoman Turks.

The Fatimids maintained trade relations with the Italian city-states like Amalfi and Genoa before the Crusades, according to the Cairo Geniza documents. A document dated 996 mentions Amalfian merchants living in Cairo. Another letter states that the Genoese had traded with Alexandria. The caliph al-Mustansir had allowed Amalfian merchants to reside in Jerusalem about 1060 in place of the Latin hospice.[11]

The Crusades led to flourishing of trade between Europe and the outremer region.[12] Genoa, Venice and Pisa created colonies in regions controlled by the Crusaders and came to control the trade with the Orient. These colonies also allowed them to trade with the Eastern world. Though the fall of the Crusader states and attempts at banning of trade relations with Muslim states by the Popes temporarily disrupted the trade with the Orient, it however continued.[13]

Europe started to revive, however, as more organized and centralized states began to form in the later Middle Ages after the Renaissance of the 12th century.

The bombardment of Algiers by the Anglo-Dutch fleet in support of an ultimatum to release European slaves, August 1816

Ottoman power based in Anatolia continued to grow, and in 1453 extinguished the Byzantine Empire with the Conquest of Constantinople. Ottomans gained control of much of the sea in the 16th century and maintained naval bases in southern France (1543–1544), Algeria and Tunisia. Barbarossa, the famous Ottoman captain is a symbol of this domination with the victory of the Battle of Preveza (1538). The Battle of Djerba (1560) marked the apex of Ottoman naval domination in the Mediterranean. As the naval prowess of the European powers increased, they confronted Ottoman expansion in the region when the Battle of Lepanto (1571) checked the power of the Ottoman Navy. This was the last naval battle to be fought primarily between galleys.

The Barbary pirates of Northwest Africa preyed on Christian shipping and coastlines in the Western Mediterranean Sea.[14] According to Robert Davis, from the 16th to 19th centuries, pirates captured 1 million to 1.25 million Europeans as slaves.[15]

The development of oceanic shipping began to affect the entire Mediterranean. Once, most of the trade between Western Europe and the East was passing through the region, but after the 1490s the development of a sea route to the Indian Ocean allowed the importation of Asian spices and other goods through the Atlantic ports of western Europe.[16][17][18]

The sea remained strategically important. British mastery of Gibraltar ensured their influence in Africa and Southwest Asia. Especially after the naval battles of Abukir (1799, Battle of the Nile) and Trafalgar (1805), the British had for a long time strengthened their dominance in the Mediterranean.[19] Wars included Naval warfare in the Mediterranean during World War I and Mediterranean theatre of World War II.

With the opening of the lockless Suez Canal in 1869, the flow of trade between Europe and Asia changed fundamentally. The fastest route now led through the Mediterranean towards East Africa and Asia. This led to a preference for the Mediterranean countries and their ports like Trieste with the direct connections to Central and Eastern Europe experienced a rapid economic rise. In the 20th century, the 1st and 2nd World War as well as the Suez Crisis and the Cold War led to a shift of trade routes to the European northern ports, which changed again towards the southern ports through European integration, the activation of the Silk Road and free world trade.[20]

Satellite image of the Mediterranean Sea at night

In 2013, the Maltese president described the Mediterranean Sea as a "cemetery" due to the large number of migrants who drowned there after their boats capsized.[21] European Parliament president Martin Schulz said in 2014 that Europe's migration policy "turned the Mediterranean into a graveyard", referring to the number of drowned refugees in the region as a direct result of the policies.[22] An Azerbaijani official described the sea as "a burial ground ... where people die".[23]

Following the 2013 Lampedusa migrant shipwreck, the Italian government decided to strengthen the national system for the patrolling of the Mediterranean Sea by authorising "Operation Mare Nostrum", a military and humanitarian mission in order to rescue the migrants and arrest the traffickers of immigrants. In 2015, more than one million migrants crossed the Mediterranean Sea into Europe.[24]

Italy was particularly affected by the European migrant crisis. Since 2013, over 700,000 migrants have landed in Italy,[25] mainly sub-Saharan Africans.[26]

The Mediterranean Sea includes 15 marginal seas:[29]

• List of seas
• Category:Marginal seas of the Mediterranean
• Category:Gulfs of the Mediterranean
• Category:Straits of the Mediterranean Sea
• Category:Channels of the Mediterranean Sea

Note 1: The International Hydrographic Organization defines the area as generic Mediterranean Sea, in the Western Basin. It does not recognize the label Sea of Sardinia.[30]

Note 2: Thracian Sea and Myrtoan Sea are seas that are part of the Aegean Sea.

Note 3: The Black Sea is not considered part of it.

Borders of the Mediterranean Sea

The International Hydrographic Organization defines the limits of the Mediterranean Sea as follows:[30] Stretching from the Strait of Gibraltar in the west to the entrances to the Dardanelles and the Suez Canal in the east, the Mediterranean Sea is bounded by the coasts of Europe, Africa, and Asia and is divided into two deep basins:

• Western Basin:
  • On the west: A line joining the extremities of Cape Trafalgar (Spain) and Cape Spartel (Africa)
  • On the northeast: The west coast of Italy. In the Strait of Messina, a line joining the north extreme of Cape Paci (15°42′E) with Cape Peloro, the east extreme of the Island of Sicily. The north coast of Sicily
  • On the east: A line joining Cape Lilibeo the western point of Sicily (37°47′N 12°22′E), through the Adventure Bank to Cape Bon (Tunisia)
• Eastern Basin:
  • On the west: The northeastern and eastern limits of the Western Basin
  • On the northeast: A line joining Kum Kale (26°11′E) and Cape Helles, the western entrance to the Dardanelles
  • On the southeast: The entrance to the Suez Canal
  • On the east: The coasts of Lebanon, Syria, and Israel

Approximate extent of the Mediterranean drainage basin (dark green). Nile basin only partially shown

The drainage basin of the Mediterranean Sea is particularly heterogeneous and extends much further than the Mediterranean region.[31] Its size has been estimated between 4,000,000 km² (1,500,000 sq mi) and 5,500,000 km² (2,100,000 sq mi),[note 1] depending on whether non-active parts (deserts) are included or not.[32][33][34] The longest river ending in the Mediterranean Sea is the Nile, which takes its sources in equatorial Africa. The basin of the Nile constitutes about two-thirds of the Mediterranean drainage basin[33] and encompasses areas as high as the Ruwenzori Mountains.[35] Among other important rivers in Africa, are the Moulouya and the Chelif, both on the north side of the Atlas Mountains. In Asia, are the Ceyhan and Seyhan, both on the south side of the Taurus Mountains.[36] In Europe, the largest basins are those of the Rhône, Ebro, Po, and Maritsa.[37] The basin of the Rhône is the largest and extends up as far north as the Jura Mountains, encompassing areas even on the north side of the Alps.[38] The basins of the Ebro, Po, and Maritsa, are respectively south of the Pyrenees, Alps, and Balkan Mountains, which are the major ranges bordering Southern Europe.

Total annual precipitation is significantly higher on the European part of the Mediterranean basin, especially near the Alps (the 'water tower of Europe') and other high mountain ranges. As a consequence, the river discharges of the Rhône and Po are similar to that of the Nile, despite the latter having a much larger basin.[36] These are the only three rivers with an average discharge of over 1,000 m³/s (35,000 cu ft/s).[33] Among large natural fresh bodies of water are Lake Victoria (Nile basin), Lake Geneva (Rhône), and the Italian Lakes (Po). While the Mediterranean watershed is bordered by other river basins in Europe, it is essentially bordered by endorheic basins or deserts elsewhere.

The following countries are in the Mediterranean drainage basin while not having a coastline on the Mediterranean Sea:

• In Europe, through various rivers:[37] Andorra,[note 2] Bulgaria,[note 3] Kosovo,[note 4] North Macedonia,[note 5] San Marino,[note 6] Serbia,[note 7] and Switzerland.[note 8]

• In Africa, through the Nile:[40] Congo, Burundi, Eritrea, Ethiopia, Kenya, Rwanda, South Sudan, Sudan, Tanzania and Uganda.

Map of the Mediterranean Sea from open Natural Earth data, 2020

The following countries have a coastline on the Mediterranean Sea:

• Northern shore (from west to east): Spain, France, Monaco, Italy, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania, Greece, Turkey.
• Eastern shore (from north to south): Turkey, Syria, Lebanon, Israel, Palestine, Egypt.
• Southern shore (from west to east): Morocco, Algeria, Tunisia, Libya, Egypt.
• Island nations: Malta, Cyprus.

Several other territories also border the Mediterranean Sea (from west to east):

• the British overseas territory of Gibraltar
• the Spanish autonomous cities of Ceuta and Melilla and nearby islands
• the Sovereign Base Areas on Cyprus
• the Palestinian Gaza Strip

Alexandria, the largest city on the Mediterranean

Barcelona, the second largest metropolitan area on the Mediterranean Sea (after Alexandria) and the headquarters of the Union for the Mediterranean

The Acropolis of Athens with the Mediterranean Sea in the background

The ancient port of Jaffa (now in Tel Aviv-Yafo), from which the biblical Jonah set sail before being swallowed by a whale[41]

Catania, Sicily, Italy, with Mount Etna in the background

İzmir, the third metropolis of Turkey (after Istanbul and Ankara)

Exclusive economic zones in Mediterranean Sea:[42][43]

Number	Country	Area (Km2)
1	Italy	541,915
2	Greece	493,708
3	Libya	355,604
4	Spain	260,000
5	Egypt	169,125
6	Algeria	128,843
7	Tunisia	102,047
8	Cyprus	98,088
9	France	88,389
10	Turkey	72,195
11	Croatia	59,032
12	Malta	55,542
13	Israel	25,139
14	Lebanon	19,265
15	Morocco	18,302
16	Albania	13,691
17	Syria	10,189
18	Montenegro	7,745
19	Palestine	2,591
20	Monaco	288
21	Slovenia	220
22	Bosnia and Herzegovina	50
23	United Kingdom	6.8
Total	Mediterranean Sea	2,500,000

The Coastline length is about 46,000 km.[44][45][46]

Major cities (municipalities), with populations larger than 200,000 people, bordering the Mediterranean Sea include:

• Algeria: Algiers, Annaba, Oran
• Egypt: Alexandria, Damietta, Port Said
• France: Marseille, Toulon, Nice
• Greece: Athens, Thessaloniki, Patras, Heraklion
• Israel: Ashdod, Haifa, Netanya, Rishon LeZion, Tel Aviv
• Italy: Bari, Catania, Genoa, Messina, Naples, Palermo, Rome, Taranto, Trieste, Venice
• Lebanon: Beirut, Tripoli
• Libya: Benghazi, Misrata, Tripoli, Zawiya, Zliten
• Malta: Valletta
• Morocco: Tétouan, Tangier
• Palestine: Gaza City
• Spain: Alicante, Almería, Badalona, Barcelona, Cartagena, Málaga, Palma de Mallorca, Valencia.
• Syria: Latakia, Tartus
• Tunisia: Sfax, Sousse, Tunis
• Turkey: Alanya, Antalya, Çanakkale, İskenderun, İzmir, Mersin

Africa (left, on horizon) and Europe (right), as seen from Gibraltar

The International Hydrographic Organization (IHO) divides the Mediterranean into a number of smaller waterbodies, each with their own designation (from west to east):[30]

• the Strait of Gibraltar
• the Alboran Sea, between Spain and Morocco
• the Balearic Sea, between mainland Spain and its Balearic Islands
• the Ligurian Sea between Corsica and Liguria (Italy)
• the Tyrrhenian Sea enclosed by Sardinia, Italian peninsula and Sicily
• the Ionian Sea between Italy, Albania and Greece
• the Adriatic Sea between Italy, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro and Albania
• the Aegean Sea between Greece and Turkey

Positano, Italy, Tyrrhenian Sea

Some other seas whose names have been in common use from the ancient times, or in the present:

• the Sea of Sardinia, between Sardinia and Balearic Islands, as a part of the Balearic Sea
• the Sea of Sicily between Sicily and Tunisia
• the Libyan Sea between Libya and Crete
• In the Aegean Sea,
  • the Thracian Sea in its north
  • the Myrtoan Sea between the Cyclades and the Peloponnese
  • the Sea of Crete north of Crete
  • the Icarian Sea between Kos and Chios
• the Cilician Sea between Turkey and Cyprus
• the Levantine Sea at the eastern end of the Mediterranean

Many of these smaller seas feature in local myth and folklore and derive their names from such associations.

View of the Saint George Bay, and snow-capped Mount Sannine from a tower in the Beirut Central District

The Port of Marseille seen from L'Estaque

Sarandë, Albania, stands on an open-sea gulf of the Ionian sea in the central Mediterranean.

In addition to the seas, a number of gulfs and straits are recognised:

• the Saint George Bay in Beirut, Lebanon
• the Ras Ibn Hani cape in Latakia, Syria
• the Ras al-Bassit cape in northern Syria.
• the Minet el-Beida ("White Harbour") bay near ancient Ugarit, Syria
• the Strait of Gibraltar, connects the Atlantic Ocean to the Mediterranean Sea and separates Spain from Morocco
• the Bay of Algeciras, at the southern end of the Iberian Peninsula
• the Gulf of Corinth, an enclosed sea between the Ionian Sea and the Corinth Canal
• the Pagasetic Gulf, the gulf of Volos, south of the Thermaic Gulf, formed by the Mount Pelion peninsula
• the Saronic Gulf, the gulf of Athens, between the Corinth Canal and the Mirtoan Sea
• the Thermaic Gulf, the gulf of Thessaloniki, located in the northern Greek region of Macedonia
• the Kvarner Gulf, Croatia
• the Gulf of Almeria, southeast of Spain
• the Gulf of Lion, south of France
• the Gulf of Valencia, east of Spain
• the Strait of Messina, between Sicily and Calabrian peninsula
• the Gulf of Genoa, northwestern Italy
• the Gulf of Venice, northeastern Italy
• the Gulf of Trieste, northeastern Italy
• the Gulf of Taranto, southern Italy
• the Gulf of Saint Euphemia, southern Italy, with the international airport nearby
• the Gulf of Salerno, southwestern Italy
• the Gulf of Gaeta, southwestern Italy
• the Gulf of Squillace, southern Italy
• the Strait of Otranto, between Italy and Albania
• the Gulf of Haifa, northern Israel
• the Gulf of Sidra, between Tripolitania (western Libya) and Cyrenaica (eastern Libya)
• the Strait of Sicily, between Sicily and Tunisia
• the Corsica Channel, between Corsica and Italy
• the Strait of Bonifacio, between Sardinia and Corsica
• the Gulf of Antalya, between west and east shores of Antalya (Turkey)
• the Gulf of İskenderun, between İskenderun and Adana (Turkey)
• the Gulf of İzmir, in İzmir (Turkey)
• the Gulf of Fethiye, in Fethiye (Turkey)
• the Gulf of Kuşadası, in İzmir (Turkey)
• the Bay of Kotor, in south-western Montenegro and south-eastern Croatia
• the Malta Channel, between Sicily and Malta
• the Gozo Channel, between Malta Island and Gozo

The two biggest islands of the Mediterranean: Sicily and Sardinia (Italy)

The Mediterranean Sea encompasses about 10,000 islands and islets, of which about 250 are permanently inhabited.[47] In the table below are listed the ten largest by size.

Much of the Mediterranean coast enjoys a hot-summer Mediterranean climate. However, most of its southeastern coast has a hot desert climate, and much of Spain's eastern (Mediterranean) coast has a cold semi-arid climate, while most of Italy's northern (Adriatic) coast has a humid subtropical climate. Although they are rare, tropical cyclones occasionally form in the Mediterranean Sea, typically in September–November.

Map of climate zones in the areas surrounding the Mediterranean Sea, according to the Köppen climate classification

Water circulation in the Mediterranean can be attributed to the surface waters entering from the Atlantic through the Strait of Gibraltar (and also low salinity water entering the Mediterranean from the Black Sea through the Bosphorus). The cool and relatively low-salinity Atlantic water circulates eastwards along the North African coasts. A part of the surface water does not pass the Strait of Sicily, but deviates towards Corsica before exiting the Mediterranean. The surface waters entering the eastern Mediterranean basin circulate along the Libyan and Israeli coasts. Upon reaching the Levantine Sea, the surface waters having warmed and increased its salinity from its initial Atlantic state, is now denser and sinks to form the Levantine Intermediate Waters (LIW). Most of the water found anywhere between 50 and 600 m deep in the Mediterranean originates from the LIW.[66] LIW are formed along the coasts of Turkey and circulate westwards along the Greek and South Italian coasts. LIW are the only waters passing the Sicily Strait westwards. After the Strait of Sicily, the LIW waters circulate along the Italian, French and Spanish coasts before exiting the Mediterranean through the depths of the Strait of Gibraltar. Deep water in the Mediterranean originates from three main areas: the Adriatic Sea, from which most of the deep water in the eastern Mediterranean originates, the Aegean Sea, and the Gulf of Lion. Deep water formation in the Mediterranean is triggered by strong winter convection fueled by intense cold winds like the Bora. When new deep water is formed, the older waters mix with the overlaying intermediate waters and eventually exit the Mediterranean. The residence time of water in the Mediterranean is approximately 100 years, making the Mediterranean especially sensitive to climate change.[67]

Being a semi-enclosed basin, the Mediterranean experiences transitory events that can affect the water circulation on short time scales. In the mid 1990s, the Aegean Sea became the main area for deep water formation in the eastern Mediterranean after particularly cold winter conditions. This transitory switch in the origin of deep waters in the eastern Mediterranean was termed Eastern Mediterranean Transient (EMT) and had major consequences on water circulation of the Mediterranean.[68][69][70]

Another example of a transient event affecting the Mediterranean circulation is the periodic inversion of the North Ionian Gyre, which is an anticyclonic ocean gyre observed in the northern part of the Ionian Sea, off the Greek coast. The transition from anticyclonic to cyclonic rotation of this gyre changes the origin of the waters fueling it; when the circulation is anticyclonic (most common), the waters of the gyre originate from the Adriatic Sea. When the circulation is cyclonic, the waters originate from the Levantine Sea. These waters have different physical and chemical characteristics, and the periodic inversion of the North Ionian Gyre (called Bimodal Oscillating System or BiOS) changes the Mediterranean circulation and biogeochemistry around the Adriatic and Levantine regions.[71]

Because of the short residence time of waters, the Mediterranean Sea is considered a hot-spot for climate change effects.[72] Deep water temperatures have increased by 0.12 °C (0.22 °F) between 1959 and 1989.[73] According to climate projections, the Mediterranean Sea could become warmer. The decrease in precipitation over the region could lead to more evaporation ultimately increasing the Mediterranean Sea salinity.[72][74] Because of the changes in temperature and salinity, the Mediterranean Sea may become more stratified by the end of the 21st century, with notable consequences on water circulation and biogeochemistry. The stratification and warming have already led to the eastern Mediterranean to become a net source of CO₂ to the atmosphere [75] [76] notably during summer. This strong summer degassing, combined with the prolonged and pronounced stratification results in the formation of aragonite crystals abiotically in the water column.[77] The cumulative warming at the surface of the Mediterranean has a significant impact on the ecological system. Extreme warming has lead to biodiversity loss [78] and presents an existential threat to some habitats [79] while making conditions more hospitable to invasive tropical species.[80]

The Mediterranean basin and sea system were established by the ancient African-Arabian continent colliding with the Eurasian continent. As Africa-Arabia drifted northward, it closed over the ancient Tethys Ocean which had earlier separated the two supercontinents Laurasia and Gondwana. At about that time in the middle Jurassic period (roughly 170 million years ago ) a much smaller sea basin, dubbed the Neotethys, was formed shortly before the Tethys Ocean closed at its western (Arabian) end. The broad line of collisions pushed up a very long system of mountains from the Pyrenees in Spain to the Zagros Mountains in Iran in an episode of mountain-building tectonics known as the Alpine orogeny. The Neotethys grew larger during the episodes of collisions (and associated foldings and subductions) that occurred during the Oligocene and Miocene epochs (34 to 5.33 mya); see animation: Africa-Arabia colliding with Eurasia. Accordingly, the Mediterranean basin consists of several stretched tectonic plates in subduction which are the foundation of the eastern part of the Mediterranean Sea. Various zones of subduction contain the highest oceanic ridges, east of the Ionian Sea and south of the Aegean. The Central Indian Ridge runs east of the Mediterranean Sea south-east across the in-between of Africa and the Arabian Peninsula into the Indian Ocean.

Messinian salinity crisis before the Zanclean flood

During Mesozoic and Cenozoic times, as the northwest corner of Africa converged on Iberia, it lifted the Betic-Rif mountain belts across southern Iberia and northwest Africa. There the development of the intramontane Betic and Rif basins created two roughly parallel marine gateways between the Atlantic Ocean and the Mediterranean Sea. Dubbed the Betic and Rifian corridors, they gradually closed during the middle and late Miocene: perhaps several times.[97] In the late Miocene the closure of the Betic Corridor triggered the so-called "Messinian salinity crisis" (MSC), characterized by the deposition of a thick evaporitic sequence - with salt deposits up to 2 km thick in the Levantine sea - and by a massive drop in water level in much of the Basin. This event was for long the subject of acute scientific controversy, now much appeased,[98] regarding its sequence, geographic range, processes leading to evaporite facies and salt deposits. The start of the MSC was recently estimated astronomically at 5.96 mya, and it persisted for some 630,000 years until about 5.3 mya;[99] see Animation: Messinian salinity crisis, at right.

After the initial drawdown and re-flooding, there followed more episodes—the total number is debated—of sea drawdowns and re-floodings for the duration of the MSC. It ended when the Atlantic Ocean last re-flooded the basin—creating the Strait of Gibraltar and causing the Zanclean flood—at the end of the Miocene (5.33 mya). Some research has suggested that a desiccation-flooding-desiccation cycle may have repeated several times, which could explain several events of large amounts of salt deposition.[100][101] Recent studies, however, show that repeated desiccation and re-flooding is unlikely from a geodynamic point of view.[102][103]

The present-day Atlantic gateway, the Strait of Gibraltar, originated in the early Pliocene via the Zanclean Flood. As mentioned, there were two earlier gateways: the Betic Corridor across southern Spain and the Rifian Corridor across northern Morocco. The Betic closed about 6 mya, causing the Messinian salinity crisis (MSC); the Rifian or possibly both gateways closed during the earlier Tortonian times, causing a "Tortonian salinity crisis" (from 11.6 to 7.2 mya), long before the MSC and lasting much longer. Both "crises" resulted in broad connections between the mainlands of Africa and Europe, which allowed migrations of flora and fauna—especially large mammals including primates—between the two continents. The Vallesian crisis indicates a typical extinction and replacement of mammal species in Europe during Tortonian times following climatic upheaval and overland migrations of new species:[104] see Animation: Messinian salinity crisis (and mammal migrations), at right.

The almost complete enclosure of the Mediterranean basin has enabled the oceanic gateways to dominate seawater circulation and the environmental evolution of the sea and basin. Circulation patterns are also affected by several other factors—including climate, bathymetry, and water chemistry and temperature—which are interactive and can induce precipitation of evaporites. Deposits of evaporites accumulated earlier in the nearby Carpathian foredeep during the Middle Miocene, and the adjacent Red Sea Basin (during the Late Miocene), and in the whole Mediterranean basin (during the MSC and the Messinian age). Many diatomites are found underneath the evaporite deposits, suggesting a connection between their formations.

Today, evaporation of surface seawater (output) is more than the supply (input) of fresh water by precipitation and coastal drainage systems, causing the salinity of the Mediterranean to be much higher than that of the Atlantic—so much so that the saltier Mediterranean waters sink below the waters incoming from the Atlantic, causing a two-layer flow across the Strait of Gibraltar: that is, an outflow submarine current of warm saline Mediterranean water, counterbalanced by an inflow surface current of less saline cold oceanic water from the Atlantic. In the 1920s, Herman Sörgel proposed the building of a hydroelectric dam (the Atlantropa project) across the Straits, using the inflow current to provide a large amount of hydroelectric energy. The underlying energy grid was also intended to support a political union between Europe and, at least, the Maghreb part of Africa (compare Eurafrika for the later impact and Desertec for a later project with some parallels in the planned grid).[105]

The end of the Miocene also marked a change in the climate of the Mediterranean basin. Fossil evidence from that period reveals that the larger basin had a humid subtropical climate with rainfall in the summer supporting laurel forests. The shift to a "Mediterranean climate" occurred largely within the last three million years (the late Pliocene epoch) as summer rainfall decreased. The subtropical laurel forests retreated; and even as they persisted on the islands of Macaronesia off the Atlantic coast of Iberia and North Africa, the present Mediterranean vegetation evolved, dominated by coniferous trees and sclerophyllous trees and shrubs with small, hard, waxy leaves that prevent moisture loss in the dry summers. Much of these forests and shrublands have been altered beyond recognition by thousands of years of human habitation. There are now very few relatively intact natural areas in what was once a heavily wooded region.

Stromboli volcano in Italy

The region has a variety of geological hazards which have closely interacted with human activity and land use patterns. Among others, in the eastern Mediterranean, the Thera eruption, dated to the 17th or 16th century BC, caused a large tsunami that some experts hypothesise devastated the Minoan civilisation on the nearby island of Crete, further leading some to believe that this may have been the catastrophe that inspired the Atlantis legend.[113] Mount Vesuvius is the only active volcano on the European mainland, while others, Mount Etna and Stromboli, are on neighbouring islands. The region around Vesuvius including the Phlegraean Fields Caldera west of Naples are quite active[114] and constitute the most densely populated volcanic region in the world where an eruptive event may occur within decades.[115]

Vesuvius itself is regarded as quite dangerous due to a tendency towards explosive (Plinian) eruptions.[116] It is best known for its eruption in AD 79 that led to the burying and destruction of the Roman cities of Pompeii and Herculaneum.

The large experience of member states and regional authorities has led to exchange on the international level with the cooperation of NGOs, states, regional and municipality authorities and private persons.[117] The Greek–Turkish earthquake diplomacy is a quite positive example of natural hazards leading to improved relations between traditional rivals in the region after earthquakes in İzmir and Athens in 1999. The European Union Solidarity Fund (EUSF) was set up to respond to major natural disasters and express European solidarity to disaster-stricken regions within all of Europe.[118] The largest amount of funding requests in the EU relates to forest fires, followed by floods and earthquakes. Forest fires, whether man-made or natural, are a frequent and dangerous hazard in the Mediterranean region.[117] Tsunamis are also an often underestimated hazard in the region. For example, the 1908 Messina earthquake and tsunami took more than 123,000 lives in Sicily and Calabria and were among the most deadly natural disasters in modern Europe.

The reticulate whipray is one of the species that colonised the Eastern Mediterranean through the Suez Canal as part of the ongoing Lessepsian migration.

The opening of the Suez Canal in 1869 created the first salt-water passage between the Mediterranean and the Red Sea. The Red Sea is higher than the Eastern Mediterranean, so the canal functions as a tidal strait that pours Red Sea water into the Mediterranean. The Bitter Lakes, which are hyper-saline natural lakes that form part of the canal, blocked the migration of Red Sea species into the Mediterranean for many decades, but as the salinity of the lakes gradually equalised with that of the Red Sea, the barrier to migration was removed, and plants and animals from the Red Sea have begun to colonise the Eastern Mediterranean. The Red Sea is generally saltier and more nutrient-poor than the Atlantic, so the Red Sea species have advantages over Atlantic species in the salty and nutrient-poor Eastern Mediterranean. Accordingly, Red Sea species invade the Mediterranean biota, and not vice versa; this phenomenon is known as the Lessepsian migration (after Ferdinand de Lesseps, the French engineer) or Erythrean ("red") invasion. The construction of the Aswan High Dam across the Nile River in the 1960s reduced the inflow of freshwater and nutrient-rich silt from the Nile into the Eastern Mediterranean, making conditions there even more like the Red Sea and worsening the impact of the invasive species.

Invasive species have become a major component of the Mediterranean ecosystem and have serious impacts on the Mediterranean ecology, endangering many local and endemic Mediterranean species. A first look at some groups of exotic species shows that more than 70% of the non-indigenous decapods and about 63% of the exotic fishes occurring in the Mediterranean are of Indo-Pacific origin,[119] introduced into the Mediterranean through the Suez Canal. This makes the Canal the first pathway of arrival of alien species into the Mediterranean. The impacts of some Lessepsian species have proven to be considerable, mainly in the Levantine basin of the Mediterranean, where they are replacing native species and becoming a familiar sight.

According to the International Union for Conservation of Nature definition, as well as Convention on Biological Diversity (CBD) and Ramsar Convention terminologies, they are alien species, as they are non-native (non-indigenous) to the Mediterranean Sea, and they are outside their normal area of distribution which is the Indo-Pacific region. When these species succeed in establishing populations in the Mediterranean Sea, compete with and begin to replace native species they are "Alien Invasive Species", as they are an agent of change and a threat to the native biodiversity. In the context of CBD, "introduction" refers to the movement by human agency, indirect or direct, of an alien species outside of its natural range (past or present). The Suez Canal, being an artificial (man-made) canal, is a human agency. Lessepsian migrants are therefore "introduced" species (indirect, and unintentional). Whatever wording is chosen, they represent a threat to the native Mediterranean biodiversity, because they are non-indigenous to this sea. In recent years, the Egyptian government's announcement of its intentions to deepen and widen the canal[120] have raised concerns from marine biologists, fearing that such an act will only worsen the invasion of Red Sea species into the Mediterranean, and lead to even more species passing through the canal.[121]

In recent decades, the arrival of exotic species from the tropical Atlantic has become noticeable. Whether this reflects an expansion of the natural area of these species that now enter the Mediterranean through the Gibraltar strait, because of a warming trend of the water caused by global warming; or an extension of the maritime traffic; or is simply the result of a more intense scientific investigation, is still an open question. While not as intense as the "Lessepsian" movement, the process may be of scientific interest and may, therefore, warrant increased levels of monitoring.

By 2100 the overall level of the Mediterranean could rise between 3 to 61 cm (1.2 to 24.0 in) as a result of the effects of climate change.[122] This could have adverse effects on populations across the Mediterranean:

• Rising sea levels will submerge parts of Malta. Rising sea levels will also mean rising salt water levels in Malta's groundwater supply and reduce the availability of drinking water.[123]
• A 30 cm (12 in) rise in sea level would flood 200 square kilometres (77 sq mi) of the Nile Delta, displacing over 500,000 Egyptians.[124]
• Cyprus wetlands are also in danger of being destroyed by the rising temperatures and sea levels.[125]

Coastal ecosystems also appear to be threatened by sea level rise, especially enclosed seas such as the Baltic, the Mediterranean and the Black Sea. These seas have only small and primarily east–west movement corridors, which may restrict northward displacement of organisms in these areas.[126] Sea level rise for the next century (2100) could be between 30 cm (12 in) and 100 cm (39 in) and temperature shifts of a mere 0.05–0.1 °C in the deep sea are sufficient to induce significant changes in species richness and functional diversity.[127]

Pollution in this region has been extremely high in recent years. The United Nations Environment Programme has estimated that 650,000,000 t (720,000,000 short tons) of sewage, 129,000 t (142,000 short tons) of mineral oil, 60,000 t (66,000 short tons) of mercury, 3,800 t (4,200 short tons) of lead and 36,000 t (40,000 short tons) of phosphates are dumped into the Mediterranean each year.[128] The Barcelona Convention aims to 'reduce pollution in the Mediterranean Sea and protect and improve the marine environment in the area, thereby contributing to its sustainable development.'[129] Many marine species have been almost wiped out because of the sea's pollution. One of them is the Mediterranean monk seal which is considered to be among the world's most endangered marine mammals.[130] The Mediterranean is also plagued by marine debris. A 1994 study of the seabed using trawl nets around the coasts of Spain, France and Italy reported a particularly high mean concentration of debris; an average of 1,935 items per km².[131]

Plastic debris accounted for 76% of debris in a 1994 study, of which 94% was plastic bags.[131]

This section is an excerpt from Marine plastic pollution.[edit]

The pathway by which plastics enters the world's oceans

Marine plastic pollution (or plastic pollution in the ocean) is a type of marine pollution by plastics, ranging in size from large original material such as bottles and bags, down to microplastics formed from the fragmentation of plastic material. Marine debris is mainly discarded human rubbish which floats on, or is suspended in the ocean. Eighty percent of marine debris is plastic.[132][133] Microplastics and nanoplastics result from the breakdown or photodegradation of plastic waste in surface waters, rivers or oceans. Recently, scientists have uncovered nanoplastics in heavy snow, more specifically about 3000 tons that cover Switzerland yearly.[134] It is estimated that there is a stock of 86 million tons of plastic marine debris in the worldwide ocean as of the end of 2013, assuming that 1.4% of global plastics produced from 1950 to 2013 has entered the ocean and has accumulated there.[135] It is estimated that 19–23 million tonnes of plastic leaks into aquatic ecosystems annually.[136] The 2017 United Nations Ocean Conference estimated that the oceans might contain more weight in plastics than fish by the year 2050.[137]

A woman and a boy collecting plastic waste at a beach during a cleanup exercise

Oceans are polluted by plastic particles ranging in size from large original material such as bottles and bags, down to microplastics formed from the fragmentation of plastic material. This material is only very slowly degraded or removed from the ocean so plastic particles are now widespread throughout the surface ocean and are known to be having deleterious effects on marine life.[138] Discarded plastic bags, six pack rings, cigarette butts and other forms of plastic waste which finish up in the ocean present dangers to wildlife and fisheries.[139] Aquatic life can be threatened through entanglement, suffocation, and ingestion.[140][141][142] Fishing nets, usually made of plastic, can be left or lost in the ocean by fishermen. Known as ghost nets, these entangle fish, dolphins, sea turtles, sharks, dugongs, crocodiles, seabirds, crabs, and other creatures, restricting movement, causing starvation, laceration, infection, and, in those that need to return to the surface to breathe, suffocation.[143] There are various types of ocean plastics causing problems to marine life. Bottle caps have been found in the stomachs of turtles and seabirds, which have died because of the obstruction of their respiratory and digestive tracts.[144] Ghost nets are also a problematic type of ocean plastic as they can continuously trap marine life in a process known as "ghost fishing".[145]

The 10 largest emitters of oceanic plastic pollution worldwide are, from the most to the least, China, Indonesia, Philippines, Vietnam, Sri Lanka, Thailand, Egypt, Malaysia, Nigeria, and Bangladesh,[146] largely through the rivers Yangtze, Indus, Yellow, Hai, Nile, Ganges, Pearl, Amur, Niger, and the Mekong, and accounting for "90 percent of all the plastic that reaches the world's oceans."[147][148] Asia was the leading source of mismanaged plastic waste, with China alone accounting for 2.4 million metric tons.[149]

Plastics accumulate because they do not biodegrade in the way many other substances do. They will photodegrade on exposure to the sun, but they do so properly only under dry conditions, and water inhibits this process.[150] In marine environments, photodegraded plastic disintegrates into ever-smaller pieces while remaining polymers, even down to the molecular level. When floating plastic particles photodegrade down to zooplankton sizes, jellyfish attempt to consume them, and in this way the plastic enters the ocean food chain.[151][152]

Solutions to marine plastic pollution, along with plastic pollution within the whole environment will be intertwined with changes in manufacturing and packaging practices, and a reduction in the usage, in particular, of single or short-lived plastic products. Many ideas exist for cleaning up plastic in the oceans including trapping plastic particles at river mouths before entering the ocean, and cleaning up the ocean gyres.[153]

A cargo ship cruises towards the Strait of Messina

Some of the world's busiest shipping routes are in the Mediterranean Sea. In particular, the Maritime Silk Road from Asia and Africa leads through the Suez Canal directly into the Mediterranean Sea to its deep-water ports in Piraeus, Trieste, Genoa, Marseilles and Barcelona. It is estimated that approximately 220,000 merchant vessels of more than 100 tonnes cross the Mediterranean Sea each year—about one-third of the world's total merchant shipping. These ships often carry hazardous cargo, which if lost would result in severe damage to the marine environment.

The discharge of chemical tank washings and oily wastes also represent a significant source of marine pollution. The Mediterranean Sea constitutes 0.7% of the global water surface and yet receives 17% of global marine oil pollution. It is estimated that every year between 100,000 t (98,000 long tons) and 150,000 t (150,000 long tons) of crude oil are deliberately released into the sea from shipping activities.

Port of Trieste

Approximately 370,000,000 t (360,000,000 long tons) of oil are transported annually in the Mediterranean Sea (more than 20% of the world total), with around 250–300 oil tankers crossing the sea every day. An important destination is the Port of Trieste, the starting point of the Transalpine Pipeline, which covers 40% of Germany's oil demand (100% of the federal states of Bavaria and Baden-Württemberg), 90% of Austria and 50% of the Czech Republic.[160] Accidental oil spills happen frequently with an average of 10 spills per year. A major oil spill could occur at any time in any part of the Mediterranean.[127]

Valencia

Barcelona

Genoa

Ambarlı

Piraeus

Fos

Marsaxlokk

La Spezia

Algeciras

Gioia Tauro

Tanger-Med

Leghorn

Evyap

Mersin

Haifa

Ashdod

Beirut

Gemlik

Nemrut Bay

Largest ports of the Mediterranean area per total vessel traffic as of 2016.[161]

Kemer Beach in Antalya on the Turkish Riviera (Turquoise Coast). In 2019, Turkey ranked sixth in the world in terms of the number of international tourist arrivals, with 51.2 million foreign tourists visiting the country.[162]

The coast of the Mediterranean has been used for tourism since ancient times, as the Roman villa buildings on the Amalfi Coast or in Barcola show. From the end of the 19th century, in particular, the beaches became places of longing for many Europeans and travellers. From then on, and especially after World War II, mass tourism to the Mediterranean began with all its advantages and disadvantages. While initially, the journey was by train and later by bus or car, today the plane is increasingly used.[163]

Tourism is today one of the most important sources of income for many Mediterranean countries, despite the man-made geopolitical conflicts in the region. The countries have tried to extinguish rising man-made chaotic zones that might affect the region's economies and societies in neighbouring coastal countries, and shipping routes. Naval and rescue components in the Mediterranean Sea are considered to be among the best due to the rapid cooperation between various naval fleets. Unlike the vast open oceans, the sea's closed position facilitates effective naval and rescue missions, considered the safest and regardless of any man-made or natural disaster.

Tourism is a source of income for small coastal communities, including islands, independent of urban centres. However, tourism has also played a major role in the degradation of the coastal and marine environment. Rapid development has been encouraged by Mediterranean governments to support the large numbers of tourists visiting the region, but this has caused serious disturbance to marine habitats by erosion and pollution in many places along the Mediterranean coasts.

Tourism often concentrates in areas of high natural wealth, causing a serious threat to the habitats of endangered species such as sea turtles and monk seals. Reductions in natural wealth may reduce the incentive for tourists to visit.[127]

Fish stock levels in the Mediterranean Sea are alarmingly low. The European Environment Agency says that more than 65% of all fish stocks in the region are outside safe biological limits and the United Nations Food and Agriculture Organisation, that some of the most important fisheries—such as albacore and bluefin tuna, hake, marlin, swordfish, red mullet and sea bream—are threatened.

There are clear indications that catch size and quality have declined, often dramatically, and in many areas, larger and longer-lived species have disappeared entirely from commercial catches.

Large open-water fish like tuna have been a shared fisheries resource for thousands of years but the stocks are now dangerously low. In 1999, Greenpeace published a report revealing that the amount of bluefin tuna in the Mediterranean had decreased by over 80% in the previous 20 years and government scientists warn that without immediate action the stock will collapse.

A study showed that climate change-related exceptional marine heatwaves in the Mediterranean Sea during 2015–2019 resulted in widespread mass sealife die-offs in five consecutive years.[164][165]