Editing Mediterranean Sea (section)

===Tectonics and paleoenvironmental analysis===
{{unreferenced section|date=October 2018}}
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&nbsp;million years ago {{dubious|date=November 2018}}) 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: [[Supercontinent|Africa-Arabia colliding with Eurasia]]. Accordingly, the Mediterranean [[Oceanic basin|basin]] consists of several stretched [[Tectonics|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 Sea|Aegean]]. The [[Central Indian Ridge]] runs east of the Mediterranean Sea south-east across the in-between{{clarify|date=August 2019}} of [[Africa]] and the [[Arabian Peninsula]] into the [[Indian Ocean]].

====Messinian salinity crisis====

[[File:Etapa3muda.jpg|thumb|upright=1.2|Messinian salinity crisis before the [[Zanclean flood]]]]
[[File:Crisis salina del Messiniense.ogv|thumb|upright=1.2|Animation: Messinian salinity crisis]]During [[Mesozoic]] and [[Cenozoic]] times, as the northwest corner of Africa converged on Iberia, it lifted the Betic-Rif [[mountain belt]]s 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 corridor|Betic]] and [[Rifian corridors]], they gradually closed during the middle and late Miocene: perhaps several times.<ref>{{cite journal |last1=de la Vara |first1=Alba |last2=Topper |first2=Robin P.M. |last3=Meijer |first3=Paul Th. |last4=Kouwenhoven |first4=Tanja J. |year=2015 |title=Water exchange through the Betic and Rifian corridors prior to the Messinian Salinity Crisis: A model study |journal=Paleoceanography |volume=30 |issue=5 |pages=548–557 |doi=10.1002/2014PA002719 |bibcode=2015PalOc..30..548D |hdl=1874/326590 |s2cid=134905445 |hdl-access=free}}</ref> In the late Miocene the closure of the [[Betic Corridor]] triggered the so-called "[[Messinian salinity crisis]]" (MSC), characterised by the deposition of a thick evaporitic sequence – with salt deposits up to 2&nbsp;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,<ref>Briand, F. (ed.) (2008). The Messinian Salinity Crisis Mega-Deposits to Microbiology – A consensus report. CIESM Publishers, Paris, Monaco. 168 p.[https://www.researchgate.net/publication/240612581]</ref> 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;<ref>{{cite journal |title=Astrochronology for the Messinian Sorbas basin (SE Spain) and orbital (precessional) forcing for evaporite cyclicity |year=2001 |doi=10.1016/S0037-0738(00)00171-8 |first1=W. |last1=Krijgsman |first2=A.R. |last2=Fortuin |first3=F.J. |last3=Hilgen |first4=F.J. |last4=Sierro |journal=[[Sedimentary Geology (journal)|Sedimentary Geology]] |volume=140 |issue=1 |pages=43–60 |bibcode=2001SedG..140...43K |hdl=1874/1632 |url=https://dspace.library.uu.nl/bitstream/1874/1632/1/Krijgsman01.pdf}}{{Dead link|date=March 2022 |bot=InternetArchiveBot |fix-attempted=yes}}</ref> see Animation: Messinian salinity crisis, at right.

After the initial drawdown{{clarify|date=August 2019}} 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.<ref>{{cite journal|author1=Gargani J., Rigollet C.|title=Mediterranean Sea level variations during the Messinian Salinity Crisis.|journal=Geophysical Research Letters|date=2007|volume=34|issue=L10405|page=L10405|doi=10.1029/2007GL029885|bibcode=2007GeoRL..3410405G|s2cid=128771539|doi-access=free}}</ref><ref>{{cite journal|author1=Gargani J.|author2=Moretti I.|author3=Letouzey J.|title=Evaporite accumulation during the Messinian Salinity Crisis: The Suez Rift Case.|journal=Geophysical Research Letters|date=2008|volume=35|issue=2|page=L02401|doi=10.1029/2007gl032494|bibcode=2008GeoRL..35.2401G|s2cid=129573384|url=https://hal.archives-ouvertes.fr/hal-00357241/file/2007GL032494.pdf|access-date=19 May 2021|archive-date=7 May 2021|archive-url=https://web.archive.org/web/20210507122326/https://hal.archives-ouvertes.fr/hal-00357241/file/2007GL032494.pdf|url-status=live}}</ref> Recent studies, however, show that repeated desiccation and re-flooding is unlikely from a [[geodynamic]] point of view.<ref>{{cite journal |last1=Govers |first1=Rob |title=Choking the Mediterranean to dehydration: The Messinian salinity crisis |journal=Geology |date=February 2009 |volume=37 |issue=2 |pages=167–170 |doi=10.1130/G25141A.1 |bibcode=2009Geo....37..167G |s2cid=34247931 }}</ref><ref name=GCV>{{cite journal |last1=Garcia-Castellanos |first1=D. |last2=Villaseñor |first2=A. |title=Messinian salinity crisis regulated by competing tectonics and erosion at the Gibraltar arc |journal=Nature |date=15 December 2011 |volume=480 |issue=7377 |pages=359–363 |doi=10.1038/nature10651 |pmid=22170684 |bibcode=2011Natur.480..359G |s2cid=205227033}}</ref>

====Desiccation and exchanges of flora and fauna====
{{See also|Pleistocene megafauna|Dwarf elephant}}
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|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:<ref>{{Cite book
 | last1 = Agusti | first1 = J
 | last2 = Moya-Sola | first2 = S
 | title = Mammal extinctions in the Vallesian (Upper Miocene)
 | volume = 30 | year = 1990 | pages = 425–432
 | issn = 1613-2580 | doi = 10.1007/BFb0011163
 | series = Lecture Notes in Earth Sciences
 | isbn = 978-3-540-52605-6
 }} (Abstract)</ref> 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 [[evaporite]]s. Deposits of evaporites accumulated earlier in the nearby [[Geology of the Western Carpathians#Foredeep|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 [[diatomite]]s are found underneath the evaporite deposits, suggesting a connection between their{{clarify|date=August 2019}} 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 [[Strait of Gibraltar#Inflow and 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 [[Eurafrique|Eurafrika]] for the later impact and [[Desertec]] for a later project with some parallels in the planned grid).<ref>Politische Geographien Europas: Annäherungen an ein umstrittenes Konstrukt, Anke Strüver, LIT Verlag Münster, 2005, p. 43</ref>

====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 forest]]s. 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.