Mediterranean Sea

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https://en.wikipedia.org/wiki/Mediterranean_Sea

 

Mediterranean Sea
Map of the Mediterranean Sea
Location	Western Europe, Southern Europe, North Africa and Western Asia
Coordinates	35°N 18°ECoordinates: 35°N 18°E
Type	Sea
Primary inflows	Atlantic Ocean, Sea of Marmara, Nile, Ebro, Rhône, Chelif, Po
Basin countries

about 24
Surface area	2,500,000 km2 (970,000 sq mi)
Average depth	1,500 m (4,900 ft)
Max. depth	5,267 m (17,280 ft)
Water volume	3,750,000 km3 (900,000 cu mi)
Residence time	80–100 years
Max. temperature	28 °C (82 °F)
Min. temperature	12 °C (54 °F)
Islands	3300+
Settlements	Alexandria, Barcelona, Algiers, Izmir, Rome, Athens, Beirut, Tripoli, Tunis, Tangier, Tel Aviv-Yafo, Split, etc.

The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the east by the Levant. The Sea has played a central role in the history of Western civilization. Although the Mediterranean is sometimes considered a part of the Atlantic Ocean, it is usually referred to as a separate body of water. Geological evidence indicates that around 5.9 million years ago, the Mediterranean was cut off from the Atlantic and was partly or completely desiccated over a period of some 600,000 years during the Messinian salinity crisis before being refilled by the Zanclean flood about 5.3 million years ago.

The Mediterranean Sea covers an area of about 2,500,000 km² (970,000 sq mi), representing 0.7% of the global ocean surface, but its connection to the Atlantic via the Strait of Gibraltar—the narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates the Iberian Peninsula in Europe from Morocco in Africa—is only 14 km (9 mi) wide. In oceanography, it is sometimes called the Eurafrican Mediterranean Sea, the European Mediterranean Sea or the African Mediterranean Sea to distinguish it from mediterranean seas elsewhere.

The Mediterranean Sea has an average depth of 1,500 m (4,900 ft) and the deepest recorded point is 5,267 m (17,280 ft) in the Calypso Deep in the Ionian Sea. It lies between latitudes 30° and 46° N and longitudes 6° W and 36° E. Its west–east length, from the Strait of Gibraltar to the Gulf of Iskenderun, on the southeastern coast of Turkey, is about 4,000 kilometres (2,500 mi). The north–south length varies greatly between different shorelines and whether only straight routes are considered. Also including longitudal changes, the shortest shipping route between the multinational Gulf of Trieste and the Libyan coastline of Gulf of Sidra is about 1,900 kilometres (1,200 mi). The water temperatures are mild in winter and warm in summer and give name to the mediterranean climate type due to the majority of precipitation falling in the cooler months. Its southern and eastern coastlines are lined with hot deserts not far inland, but the immediate coastline on all sides of the Mediterranean tends to have strong maritime moderation.

The sea was an important route for merchants and travelers of ancient times, facilitating trade and cultural exchange between peoples of the region. The history of the Mediterranean region is crucial to understanding the origins and development of many modern societies. The Roman Empire maintained nautical hegemony over the sea for centuries.

The countries surrounding the Mediterranean in clockwise order are Spain, France, Monaco, Italy, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania, Greece, Turkey, Syria, Lebanon, Israel, Egypt, Libya, Tunisia, Algeria, and Morocco; Malta and Cyprus are island countries in the sea. In addition, the Gaza Strip and the British Overseas Territories of Gibraltar and Akrotiri and Dhekelia have coastlines on the sea.

History

Main article: History of the Mediterranean region

Ancient civilizations

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.

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.

Two of the most notable Mediterranean civilizations in classical antiquity were the Greek city states 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.

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 was 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.

Middle Ages and empires

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 Arab Empire controlled 75% 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.

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.

The Crusades led to flourishing of trade between Europe and the outremer region. 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.

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. According to Robert Davis, from the 16th to 19th centuries, pirates captured 1 million to 1.25 million Europeans as slaves.

The development of oceanic shipping began to affect the entire Mediterranean. Once, most trade between Western Europe and the East had passed 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.

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. 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.

21st century and migrations

Further information: European migrant crisis, List of migrant vessel incidents on the Mediterranean Sea, and Timeline of the European migrant crisis

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. 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. An Azerbaijani official described the sea as "a burial ground ... where people die".

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.

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

Geography

A satellite image showing the Mediterranean Sea. The Strait of Gibraltar appears in the bottom left (north-west) quarter of the image; to its left is the Iberian Peninsula in Europe, and to its right, the Maghreb in Africa.

 

The Dardanelles strait in Turkey. The north (upper) side forms part of Europe (the Gelibolu Peninsula in the Thrace region); on the south (lower) side is Anatolia in Asia.

The Mediterranean Sea connects:

• to the Atlantic Ocean by the Strait of Gibraltar (known in Homer's writings as the "Pillars of Hercules") in the west
• to the Sea of Marmara and the Black Sea, by the Straits of the Dardanelles and the Bosporus respectively, in the east

The 163 km (101 mi) long artificial Suez Canal in the southeast connects the Mediterranean Sea to the Red Sea without ship lock, because the water level is essentially the same.

The westernmost point of the Mediterranean is located at the transition from the Alborán Sea to the Strait of Gibraltar, the easternmost point is on the coast of the Gulf of Iskenderun in southeastern Turkey. The northernmost point of the Mediterranean is on the coast of the Gulf of Trieste near Monfalcone in northern Italy while the southernmost point is on the coast of the Gulf of Sidra near the Libyan town of El Agheila.

Large islands in the Mediterranean include:

• Cyprus, Crete, Euboea, Rhodes, Lesbos, Chios, Kefalonia, Corfu, Limnos, Samos, Naxos, and Andros in the Eastern Mediterranean
• Sicily, Cres, Krk, Brač, Hvar, Pag, Korčula, and Malta in the central Mediterranean
• Sardinia, Corsica, and the Balearic Islands: Ibiza, Majorca, and Menorca in the Western Mediterranean

The Alpine arc, which also has a great meteorological impact on the Mediterranean area, touches the Mediterranean in the west in the area around Nice.

The typical Mediterranean climate has hot, dry summers and mild, rainy winters. Crops of the region include olives, grapes, oranges, tangerines, carobs and cork.

Marginal seas

The Mediterranean Sea includes 15 marginal seas:

Number	Sea	Area (km2)	Marginal countries and territories
1	Libyan Sea	350,000	Libya, Greece, Malta, Italy
2	Levantine Sea	320,000	Turkey, Syria, Lebanon, Israel, Palestine, Egypt, Greece, Cyprus, Akrotiri & Dhekelia
3	Tyrrhenian Sea	275,000	Italy, France
4	Aegean Sea	214,000	Turkey, Greece
5	Icarian Sea	(Part of Aegean)	Greece
6	Myrtoan Sea	(Part of Aegean)	Greece
7	Thracian Sea	(Part of Aegean)	Greece, Turkey
8	Ionian Sea	169,000	Greece, Albania, Italy
9	Balearic Sea	150,000	France, Spain
10	Adriatic Sea	138,000	Albania, Bosnia and Herzegovina, Croatia, Italy, Montenegro, Slovenia
11	Sea of Sardinia	120,000	Italy, Spain
12	Sea of Crete	95,000	Greece, Libya, Egypt
13	Ligurian Sea	80,000	Italy, France
14	Alboran Sea	53,000	Spain, Morocco, Algeria, Gibraltar
15	Sea of Marmara	11,500	Turkey
–	Other	~500,000	Consists of gulfs, straits, channels and other parts that do not have the name of a specific sea.
Total	Mediterranean Sea	~2,500,000

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.

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.

Extent

Borders of the Mediterranean Sea.

 

The Çanakkale 1915 Bridge on the Dardanelles strait, connecting Europe and Asia, will become the longest suspension bridge in the world.

The International Hydrographic Organization defines the limits of the Mediterranean Sea as follows: 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

Coastal countries

For a more comprehensive list, see List of Mediterranean countries.

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

 

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

 

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

Exclusive economic zone

Exclusive economic zones in Mediterranean Sea:

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

Coastline length

The Coastline length is about 46,000 km.

Coastal cities

For a more comprehensive list, see List of coastal settlements of the Mediterranean Sea.

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

Country	Cities
Algeria	Algiers, Annaba, Oran
Egypt	Alexandria, Damietta, Port Said
France	Marseille, Toulon, Nice
Greece	Athens, Thessaloniki, Patras, Heraklion
Israel	Ashdod, Haifa, Netanya, 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, Ayvalık, Bodrum, Çanakkale, Çeşme, Fethiye, Foça, İskenderun, Kemer, Kuşadası, Marmaris, Mersin.

Subdivisions

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):

• 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

Other seas

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.

Other features

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 İskenderun, between İskenderun and Adana (Turkey)
• the Gulf of Antalya, between west and east shores of Antalya (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

Ten largest islands by area

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

 

Main article: List of islands in the Mediterranean

Country	Island	Area in km2	Population
Italy	Sicily	25,460	5,048,995
Italy	Sardinia	23,821	1,672,804
Cyprus	Cyprus	9,251	1,088,503
France	Corsica	8,680	299,209
Greece	Crete	8,336	623,666
Greece	Euboea	3,655	218.000
Spain	Majorca	3,640	869,067
Greece	Lesbos	1,632	90,643
Greece	Rhodes	1,400	117,007
Greece	Chios	842	51,936

Climate

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

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. Although they are rare, tropical cyclones occasionally form in the Mediterranean Sea, typically in September–November.

Sea temperature

Mean sea temperature (°C)

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Málaga	16	15	16	16	18	20	22	23	22	20	18	17	18.6
Barcelona	13	12	13	14	17	20	23	25	23	20	17	15	17.8
Marseille	13	13	13	14	16	18	21	22	21	18	16	14	16.6
Naples	15	14	14	15	18	22	25	27	25	22	19	16	19.3
Malta	16	16	15	16	18	21	24	26	25	23	21	18	19.9
Venice	11	10	11	13	18	22	25	26	23	20	16	14	17.4
Athens	16	15	15	16	18	21	24	24	24	21	19	18	19.3
Heraklion	16	15	15	16	19	22	24	25	24	22	20	18	19.7
Antalya	17	17	16	17	21	24	27	29	27	25	22	19	21.8
Limassol	18	17	17	18	20	24	26	28	27	25	22	19	21.7
Mersin	18	17	17	18	21	25	28	29	28	25	22	19	22.3
Tel Aviv	18	17	17	18	21	24	27	28	28	26	23	20	22.3
Alexandria	18	17	17	18	20	23	25	26	26	25	22	20	21.4

Oceanography

Predominant surface currents for June

Being nearly landlocked affects conditions in the Mediterranean Sea: for instance, tides are very limited as a result of the narrow connection with the Atlantic Ocean. The Mediterranean is characterised and immediately recognised by its deep blue colour.

Evaporation greatly exceeds precipitation and river runoff in the Mediterranean, a fact that is central to the water circulation within the basin. Evaporation is especially high in its eastern half, causing the water level to decrease and salinity to increase eastward. The average salinity in the basin is 38 PSU at 5 m depth. The temperature of the water in the deepest part of the Mediterranean Sea is 13.2 °C (55.8 °F).

The net water influx from the Atlantic Ocean is ca. 70,000 m³/s or 2.2×10¹² m³/a (7.8×10¹³ cu ft/a). Without this Atlantic water, the sea level of the Mediterranean Sea would fall at a rate of about 1 m per year.

General circulation

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. 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.

Other events affecting water circulation

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.

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.

Climate change

Because of the short residence time of waters, the Mediterranean Sea is considered a hot-spot for climate change effects. Deep water temperatures have increased by 0.12 °C (0.22 °F) between 1959 and 1989. 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. 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.

Biogeochemistry

In spite of its great biodiversity, concentrations of chlorophyll and nutrients in the Mediterranean Sea are very low, making it one of the most oligotrophic ocean regions in the world. The Mediterranean Sea is commonly referred to as an LNLC (Low-Nutrient, Low-Chlorophyll) area. The Mediterranean Sea fits the definition of a desert in which its nutrient contents are low, making it difficult for plants and animals to develop.

There are steep gradients in nutrient concentrations, chlorophyll concentrations and primary productivity in the Mediterranean. Nutrient concentrations in the western part of the basin are about double the concentrations in the eastern basin. The Alboran Sea, close to the Strait of Gibraltar, has a daily primary productivity of about 0.25 g C (grams of carbon) m⁻² day⁻¹ whereas the eastern basin has an average daily productivity of 0.16 g C m⁻² day⁻¹. For this reason, the eastern part of the Mediterranean Sea is termed "ultraoligotrophic". The productive areas of the Mediterranean Sea are few and small. High (i.e. more than 0.5 grams of Chlorophyll a per cubic meter) productivity occurs in coastal areas, close to the river mouths which are the primary suppliers of dissolved nutrients. The Gulf of Lion has a relatively high productivity because it is an area of high vertical mixing, bringing nutrients to the surface waters that can be used by phytoplankton to produce Chlorophyll a.

Primary productivity in the Mediterranean is also marked by an intense seasonal variability. In winter, the strong winds and precipitation over the basin generate vertical mixing, bringing nutrients from the deep waters to the surface, where phytoplankton can convert it into biomass. However, in winter, light may be the limiting factor for primary productivity. Between March and April, spring offers the ideal trade-off between light intensity and nutrient concentrations in surface for a spring bloom to occur. In summer, high atmospheric temperatures lead to the warming of the surface waters. The resulting density difference virtually isolates the surface waters from the rest of the water column and nutrient exchanges are limited. As a consequence, primary productivity is very low between June and October.

Oceanographic expeditions uncovered a characteristic feature of the Mediterranean Sea biogeochemistry: most of the chlorophyll production does not occur on the surface, but in sub-surface waters between 80 and 200 meters deep. Another key characteristic of the Mediterranean is its high nitrogen-to-phosphorus ratio (N:P). Redfield demonstrated that most of the world's oceans have an average N:P ratio around 16. However, the Mediterranean Sea has an average N:P between 24 and 29, which translates a widespread phosphorus limitation.

Because of its low productivity, plankton assemblages in the Mediterranean Sea are dominated by small organisms such as picophytoplankton and bacteria.

Geology

See also: Geology and paleoclimatology of the Mediterranean Basin

A submarine karst spring, called vrulja, near Omiš; observed through several ripplings of an otherwise calm sea surface.

The geologic history of the Mediterranean Sea is complex. Underlain by oceanic crust, the sea basin was once thought to be a tectonic remnant of the ancient Tethys Ocean; it is now known to be a structurally younger basin, called the Neotethys, which was first formed by the convergence of the African and Eurasian plates during the Late Triassic and Early Jurassic. Because it is a near-landlocked body of water in a normally dry climate, the Mediterranean is subject to intensive evaporation and the precipitation of evaporites. The Messinian salinity crisis started about six million years ago (mya) when the Mediterranean became landlocked, and then essentially dried up. There are salt deposits accumulated on the bottom of the basin of more than a million cubic kilometres—in some places more than three kilometres thick.

Scientists estimate that the sea was last filled about 5.3 million years ago (mya) in less than two years by the Zanclean flood. Water poured in from the Atlantic Ocean through a newly breached gateway now called the Strait of Gibraltar at an estimated rate of about three orders of magnitude (one thousand times) larger than the current flow of the Amazon River.

The Mediterranean Sea has an average depth of 1,500 m (4,900 ft) and the deepest recorded point is 5,267 m (17,280 ft) in the Calypso Deep in the Ionian Sea. The coastline extends for 46,000 km (29,000 mi). A shallow submarine ridge (the Strait of Sicily) between the island of Sicily and the coast of Tunisia divides the sea in two main subregions: the Western Mediterranean, with an area of about 850,000 km² (330,000 mi²); and the Eastern Mediterranean, of about 1.65 million km² (640,000 mi²). Coastal areas have submarine karst springs or vruljas, which discharge pressurised groundwater into the water from below the surface; the discharge water is usually fresh, and sometimes may be thermal.

Tectonics and paleoenvironmental analysis

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

Messinian salinity crisis before the Zanclean flood

 

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Animation: Messinian salinity crisis

Main article: Messinian salinity crisis

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. In the late Miocene the closure of the Betic Corridor triggered the so-called "Messinian salinity crisis" (MSC), when the Mediterranean almost entirely dried out. 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; 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. Recent studies, however, show that repeated desiccation and re-flooding is unlikely from a geodynamic point of view.

Desiccation and exchanges of flora and fauna

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.

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).

Shift to a "Mediterranean climate"

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.

Paleoclimate

Because of its latitude and its landlocked position, the Mediterranean is especially sensitive to astronomically induced climatic variations, which are well documented in its sedimentary record. Since the Mediterranean is subject to the deposition of eolian dust from the Sahara during dry periods, whereas riverine detrital input prevails during wet ones, the Mediterranean marine sapropel-bearing sequences provide high-resolution climatic information. These data have been employed in reconstructing astronomically calibrated time scales for the last 9 Ma of the Earth's history, helping to constrain the time of past geomagnetic reversals. Furthermore, the exceptional accuracy of these paleoclimatic records has improved our knowledge of the Earth's orbital variations in the past.

Biodiversity

Unlike the vast multidirectional ocean currents in open oceans within their respective oceanic zones; biodiversity in the Mediterranean Sea is that of a stable one due to the subtle but strong locked nature of currents which affects favorably, even the smallest macroscopic type of volcanic life form. The stable marine ecosystem of the Mediterranean Sea and sea temperature provides a nourishing environment for life in the deep sea to flourish while assuring a balanced aquatic ecosystem excluded from any external deep oceanic factors. It is estimated that there are more than 17,000 marine species in the Mediterranean Sea with generally higher marine biodiversity in coastal areas, continental shelves, and decreases with depth.

As a result of the drying of the sea during the Messinian salinity crisis, the marine biota of the Mediterranean are derived primarily from the Atlantic Ocean. The North Atlantic is considerably colder and more nutrient-rich than the Mediterranean, and the marine life of the Mediterranean has had to adapt to its differing conditions in the five million years since the basin was reflooded.

The Alboran Sea is a transition zone between the two seas, containing a mix of Mediterranean and Atlantic species. The Alboran Sea has the largest population of bottlenose dolphins in the Western Mediterranean, is home to the last population of harbour porpoises in the Mediterranean, and is the most important feeding grounds for loggerhead sea turtles in Europe. The Alboran Sea also hosts important commercial fisheries, including sardines and swordfish. The Mediterranean monk seals live in the Aegean Sea in Greece. In 2003, the World Wildlife Fund raised concerns about the widespread drift net fishing endangering populations of dolphins, turtles, and other marine animals such as the spiny squat lobster.

There was a resident population of killer whale in the Mediterranean until the 1980s, when they went extinct, probably due to longterm PCB exposure. There are still annual sightings of killer whale vagrants.

See also: Specially Protected Areas of Mediterranean Importance, List of fish of the Mediterranean Sea, and List of fish of the Black Sea

Environmental issues

For 4,000 years, human activity has transformed most parts of Mediterranean Europe, and the "humanisation of the landscape" overlapped with the appearance of the present Mediterranean climate. The image of a simplistic, environmental determinist notion of a Mediterranean paradise on Earth in antiquity, which was destroyed by later civilisations, dates back to at least the 18th century and was for centuries fashionable in archaeological and historical circles. Based on a broad variety of methods, e.g. historical documents, analysis of trade relations, floodplain sediments, pollen, tree-ring and further archaeometric analyses and population studies, Alfred Thomas Grove's and Oliver Rackham's work on "The Nature of Mediterranean Europe" challenges this common wisdom of a Mediterranean Europe as a "Lost Eden", a formerly fertile and forested region, that had been progressively degraded and desertified by human mismanagement. The belief stems more from the failure of the recent landscape to measure up to the imaginary past of the classics as idealised by artists, poets and scientists of the early modern Enlightenment.

The thermonuclear bomb that fell into the sea recovered off Palomares, Almería, 1966

The historical evolution of climate, vegetation and landscape in southern Europe from prehistoric times to the present is much more complex and underwent various changes. For example, some of the deforestation had already taken place before the Roman age. While in the Roman age large enterprises such as the latifundia took effective care of forests and agriculture, the largest depopulation effects came with the end of the empire. Some assume that the major deforestation took place in modern times—the later usage patterns were also quite different e.g. in southern and northern Italy. Also, the climate has usually been unstable and there is evidence of various ancient and modern "Little Ice Ages", and plant cover accommodated to various extremes and became resilient to various patterns of human activity.

Human activity was therefore not the cause of climate change but followed it. The wide ecological diversity typical of Mediterranean Europe is predominantly based on human behavior, as it is and has been closely related human usage patterns. The diversity range was enhanced by the widespread exchange and interaction of the longstanding and highly diverse local agriculture, intense transport and trade relations, and the interaction with settlements, pasture and other land use. The greatest human-induced changes, however, came after World War II, in line with the "1950s syndrome" as rural populations throughout the region abandoned traditional subsistence economies. Grove and Rackham suggest that the locals left the traditional agricultural patterns and instead became scenery-setting agents for tourism. This resulted in more uniform, large-scale formations. Among further current important threats to Mediterranean landscapes are overdevelopment of coastal areas, abandonment of mountains and, as mentioned, the loss of variety via the reduction of traditional agricultural occupations.

Natural hazards

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. 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 and constitute the most densely populated volcanic region in the world where an eruptive event may occur within decades.

Vesuvius itself is regarded as quite dangerous due to a tendency towards explosive (Plinian) eruptions. 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 cooperation of NGOs, states, regional and municipality authorities and private persons. 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. 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. 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 was among the most deadly natural disasters in modern Europe.

Invasive species

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,^[104] 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 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.

Arrival of new tropical Atlantic species

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.

Sea-level rise

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. 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.
• 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.
• Cyprus wetlands are also in danger of being destroyed by the rising temperatures and sea levels.

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. 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.

Pollution

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. 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.' 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.

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. Plastic debris accounted for 76%, of which 94% was plastic bags.

Shipping

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. 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.

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.

Tourism

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.

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 travelers. 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.

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 neighboring 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 centers. However, tourism has also played 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.

See also: Environmental impact of tourism

Overfishing

Main article: Overfishing

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.

Faint young Sun paradox

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Faint_young_Sun_paradox 

 

Artist's depiction of the life cycle of a Sun-like star, starting as a main-sequence star at lower left then expanding through the subgiant and giant phases, until its outer envelope is expelled to form a planetary nebula at upper right.

The faint young Sun paradox or faint young Sun problem describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the Sun's output would be only 70 percent as intense during that epoch as it is during the modern epoch. The paradox is this: with the young sun's output at only 70 percent of its current output, early Earth would be expected to be completely frozen – but early Earth seems to have had liquid water.

The issue was raised by astronomers Carl Sagan and George Mullen in 1972. Proposed resolutions of this paradox have taken into account greenhouse effects, changes to planetary albedo, astrophysical influences, or combinations of these suggestions.

An unresolved question is how a climate suitable for life was maintained on Earth over the long timescale despite the variable solar output and wide range of terrestrial conditions.

Solar evolution

Life timeline
−4500 — – — – −4000 — – — – −3500 — – — – −3000 — – — – −2500 — – — – −2000 — – — – −1500 — – — – −1000 — – — – −500 — – — – 0 —	Water   Single-celled life   Photosynthesis   Eukaryotes   Multicellular life   P l a n t s   Arthropods Molluscs Flowers Dinosaurs   Mammals Birds Primates H a d e a n A r c h e a n P r o t e r o z o i c P h a n e r o z o i c	← Earth formed ← Earliest water ← Earliest known life ← LHB meteorites ← Earliest oxygen ← Pongola glaciation* ← Atmospheric oxygen ← Huronian glaciation* ← Sexual reproduction ← Earliest multicellular life ← Earliest fungi ← Earliest plants ← Earliest animals ← Cryogenian ice age* ← Ediacaran biota ← Cambrian explosion ← Andean glaciation* ← Earliest tetrapods ← Karoo ice age* ← Earliest apes / humans ← Quaternary ice age*
(million years ago) *Ice Ages

Early in Earth's history, the Sun's output would have been only 70 percent as intense as it is during the modern epoch, owing to a higher ratio of hydrogen to helium in its core. Since then, the Sun has gradually brightened and consequently warmed Earth's surface, a process known as radiative forcing. During the Archaean age, assuming, constant albedo, and other surface features, such as greenhouse gases, Earth's equilibrium temperature would have been too low to sustain a liquid ocean. Astronomers Carl Sagan and George Mullen pointed out in 1972 that this is contrary to the geological and paleontological evidence.

The sun is powered by nuclear fusion, which, for the Sun can be represented in the following way:

${\displaystyle {\ce {4^{1}H -> ^{4}He + 2e+ + 2\nu}}}$

${\displaystyle {\ce {4^{1}H + e- -> ^{4}He + e+ + 2\nu}}}$

In the equations above, e⁺ is a positron, e⁻ is an electron and ${\displaystyle {\ce {\nu}}}$ represents a neutrino (nearly massless). The net effect is three-fold: a release of energy by Einstein's formula ΔE = mc² (since the helium nucleus is less massive than the hydrogen nuclei), an increase in the density of the solar core (since the final product is contained in one nucleus as opposed to between four different protons), and an increase in the rate of fusion (since higher temperatures help increase the collision speed between the four protons and boost the likelihood that such reactions take place). The net effect is an associated increase in solar luminosity. More recent modeling studies have shown that the Sun is currently 1.4 times brighter today than it was 4.6 billion years ago (Ga), and that it has brightened roughly linearly since then with time, though it has accelerated slightly.

Despite the reduced solar luminosity 4 billion (4 × 10⁹) years ago and with greenhouse gas, the geological record shows a continually relatively warm surface in the full early temperature record of Earth, with the exception of a cold phase, the Huronian glaciation, about 2.4 to 2.1 billion years ago. Water-related sediments have been found dating to as early as 3.8 billion years ago. This relationship between surface temperature and the balance of forcing mechanisms has implications for how scientists understand the evolution of early life forms, which have been dated from as early as 3.5 billion years.

Greenhouse gas solutions

Ammonia as a greenhouse gas

Sagan and Mullen even suggested during their descriptions of the paradox that it might be solved by high concentrations of ammonia gas, NH₃. However, it has since been shown that while ammonia is an effective greenhouse gas, it is easily photochemically destroyed in the atmosphere and converted to nitrogen (N₂) and hydrogen (H₂) gases. It was suggested (again by Sagan) that a photochemical haze could have prevented this destruction of ammonia and allowed it to continue acting as a greenhouse gas during this time, however this idea was later tested using a photochemical model and discounted. Furthermore, such a haze is thought to have cooled Earth's surface beneath it and counteracted the greenhouse effect.

Carbon dioxide as a greenhouse gas

This conceptual graph shows the relationship between solar radiation and the greenhouse effect – in this case dominated by modulations in carbon dioxide.

It is now thought that carbon dioxide was present in higher concentrations during this period of lower solar radiation. It was first proposed and tested as part of Earth's atmospheric evolution in the late 70s. An atmosphere that contained about 1000 times the Present Atmospheric Level (or PAL) was found to be consistent with the evolutionary path of Earth's carbon cycle and solar evolution.

The primary mechanism for attaining such high CO₂ concentrations is the carbon cycle. On large timescales, the inorganic branch of the carbon cycle, which is known as the carbonate–silicate cycle is responsible for determining the partitioning of CO₂ between the atmosphere and the surface of Earth. In particular, during a time of low surface temperatures, rainfall and weathering rates would be reduced, allowing for the build-up of carbon dioxide in the atmosphere on timescales of 0.5 million years (Myr).

Specifically, using 1-D models, which represent Earth as a single point (instead of something that varies across 3 dimensions) scientists have determined that at 4.5 Ga, with a 30% dimmer Sun, a minimum partial pressure of 0.1 bar of CO₂ is required to maintain an above-freezing surface temperature. At a maximum, 10 bar of CO₂ has been suggested as a plausible upper limit.

The exact amount of carbon dioxide levels is still under debate, however. In 2001, Sleep and Zahnle suggested that increased weathering on the seafloor on a young, tectonically active Earth could have reduced carbon dioxide levels. Then in 2010, Rosing et al. analyzed marine sediments called banded iron formations (BIFs), and found large amounts of various iron-rich minerals, including magnetite (Fe₃O₄), an oxidized mineral alongside siderite (FeCO₃), a reduced mineral and saw that they formed during the first half of Earth's history (and not afterward). The minerals' relative coexistence suggested an analogous balance between CO₂ and H₂. In the analysis, Rosing et al. connected the atmospheric H₂ concentrations with regulation by biotic methanogenesis. Anaerobic, single-celled organisms that produced methane (CH₄) may therefore have contributed to the warming in addition to carbon dioxide.

Other proposed explanations

Phanerozoic Climate Change

A minority view, propounded by the Israeli-American physicist Nir Shaviv, uses climatological influences of solar wind, combined with a hypothesis of Danish physicist Henrik Svensmark for a cooling effect of cosmic rays, to explain the paradox. According to Shaviv, the early Sun had emitted a stronger solar wind that produced a protective effect against cosmic rays. In that early age, a moderate greenhouse effect comparable to today's would have been sufficient to explain an ice-free Earth. Evidence for a more active early Sun has been found in meteorites.

The temperature minimum around 2.4 billion years goes along with a cosmic ray flux modulation by a variable star formation rate in the Milky Way. The reduced solar impact later results in a stronger impact of cosmic ray flux (CRF), which is hypothesized to lead to a relationship with climatological variations.

Mass loss from Sun

It has been proposed several times that mass loss from the faint young Sun in the form of stronger solar winds could have compensated for the low temperatures from greenhouse gas forcing. In this framework, the early Sun underwent an extended period of higher solar wind output. This caused a mass loss from the Sun on the order of 5−10 percent over its lifetime, resulting in a more consistent level of solar luminosity (as the early Sun had more mass, resulting in more energy output than was predicted). In order to explain the warm conditions in the Archean era, this mass loss must have occurred over an interval of about one billion years. Records of ion implantation from meteorites and lunar samples show that the elevated rate of solar wind flux only lasted for a period of 0.1 billion years. Observations of the young Sun-like star π¹ Ursae Majoris matches this rate of decline in the stellar wind output, suggesting that a higher mass loss rate can not by itself resolve the paradox.

Changes in clouds

If greenhouse gas concentrations did not compensate completely for the fainter sun, the moderate temperature range may be explained by a lower surface albedo. At the time, a smaller area of exposed continental land would have resulted in fewer cloud condensation nuclei both in the form of wind-blown dust and biogenic sources. A lower albedo allows a higher fraction of solar radiation to penetrate to the surface. Goldblatt and Zahnle (2011) investigated whether a change in cloud fraction could have been sufficiently warming and found that the net effect was equally likely to have been negative as positive. At most the effect could have raised surface temperatures to just above freezing on average.

Another proposed mechanism of cloud cover reduction relates a decrease in cosmic rays during this time to reduced cloud fraction. However, this mechanism does not work for several reasons, including the fact that ions do not limit cloud formation as much as CCN, and cosmic rays have been found to have little impact on global mean temperature.

Clouds continue to be the dominant source of uncertainty in 3-D global climate models, and a consensus has yet to be reached on exactly how changes in cloud spatial patterns and cloud type may have affected Earth's climate during this time.

Gaia hypothesis

The Gaia hypothesis holds that biological processes work to maintain a stable surface climate on Earth to maintain habitability through various negative feedback mechanisms. While organic processes, such as the organic carbon cycle, work to regulate dramatic climate changes, and that the surface of Earth has presumably remained habitable, this hypothesis has been criticized as intractable. Furthermore, life has existed on the surface of Earth through dramatic changes in climate, including Snowball Earth episodes. There are also strong and weak versions of the Gaia hypothesis, which has caused some tension in this research area.

On other planets

Mars

Mars has its own version of the faint young Sun paradox. Martian terrains show clear signs of past liquid water on the surface, including outflow channels, gullies, modified craters, and valley networks. These geomorphic features suggest Mars had an ocean on its surface and river networks that resemble current Earth's during the late Noachian (4.1–3.7 Ga). It is unclear how Mars's orbital pattern, which places it even further from the Sun, and the faintness of the young Sun could have produced what is thought to have been a very warm and wet climate on Mars. Scientists debate over which geomorphological features can be attributed to shorelines or other water flow markers and which can be ascribed to other mechanisms. Nevertheless, the geologic evidence, including observations of widespread fluvial erosion in the southern highlands, are generally consistent with an early warm and semi-arid climate.

Given the orbital and solar conditions of early Mars, a greenhouse effect would have been necessary to boost surface temperatures at least 65 K in order for these surface features to have been carved by flowing water. A much denser, CO₂-dominated atmosphere has been proposed as a way to produce such a temperature increase. This would depend upon the carbon cycle and the rate of volcanism throughout the pre-Noachian and Noachian, which is not well known. Volatile outgassing is thought to have occurred during these periods.

One way to ascertain whether Mars possessed a thick CO₂-rich atmosphere is to look at carbonate deposits. A primary sink for carbon in Earth's atmosphere is the carbonate–silicate cycle. It is however hard for CO₂ to have built up in the Martian atmosphere in this way because the greenhouse effect would have been outstripped by CO₂ condensation.

A volcanically-outgassed CO₂-H₂ greenhouse is one of the most potent warming solutions recently suggested for early Mars. Intermittent bursts of methane may have been another possibility. Such greenhouse gas combinations appear necessary because carbon dioxide alone, even at pressures exceeding a few bar, cannot explain the temperatures required for the presence of surface liquid water on early Mars.

Venus

Venus's atmosphere is composed of 96% carbon dioxide, and during this time, billions of years ago, when the Sun was 25 to 30% dimmer Venus's surface temperature could have been much cooler, and its climate could have resembled current Earth's, complete with a hydrological cycle – before it experienced a runaway greenhouse effect.