Mediterranean Sea

Its semi-enclosed configuration makes the oceanic gateways critical in controlling circulation and environmental evolution in the Mediterranean Sea. Water circulation patterns are driven by a number of interactive factors, such as climate and bathymetry, which can lead to precipitation of evaporites. During late Miocene times, a so-called "Messinian Salinity Crisis" (MSC hereafter) occurred, which was triggered by the closure of the Atlantic gateway. Evaporites accumulated in the Red Sea Basin (late Miocene), in the Carpatian foredeep (middle Miocene) and in the whole Mediterranean area (Messinian). An accurate age estimate of the MSC—5.96 Ma—has recently been astronomically achieved; furthermore, this event seems to have occurred synchronously. The beginning of the MSC is supposed to have been of tectonic origin; however, an astronomical control (eccentricity) might also have been involved. In the Mediterranean basin, diatomites are regularly found underneath the evaporitic deposits, thus suggesting (albeit not clearly so far) a connection between their geneses. The present-day Atlantic gateway, i.e. the Strait of Gibraltar, finds its origin in the early Pliocene. However, two other connections between the Atlantic Ocean and the Mediterranean Sea existed in the past: the Betic Corridor (southern Spain) and the Rifian Corridor (northern Morocco). The former closed during Tortonian times, thus providing a "Tortonian Salinity Crisis" well before the MSC; the latter closed about 6 Ma, allowing exchanges in the mammal fauna between Africa and Europe. Nowadays, evaporation is more relevant than the water yield supplied by riverine water and precipitation, so that salinity in the Mediterranean is higher than in the Atlantic. These conditions result in the outflow of warm saline Mediterranean deep water across Gibraltar, which is in turn counterbalanced by an inflow of a less saline surface current of cold oceanic water.

In the last few centuries, mankind has done much to alter Mediterranean geology. Structures have been built all along the coastlines, exacerbating and rerouting erosional patterns. Many pollution-producing boats travel the sea that unbalance the natural chemical ratios of the region. Beaches have been mismanaged, and the overuse of the sea's natural and marine resources continues to be a problem. This misuse speeds along and/or confounds natural processes. The actual geography has also been altered by the building of dams and canals.

The Mediterranean was once thought to be the remnant of the Tethys Ocean. It is now known to be a structurally younger ocean basin known as Neotethys. Neotethys formed during the Late Triassic and Early Jurassic rifting of the African and Eurasian plates.

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Ecology and global warming

As a result of the drying of the sea during the Messinian Salinity Crisis^[7], 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 thousand years since the basin was reflooded.

The opening of the Suez Canal in 1869 created the first salt-water passage between the Mediterranean and Red Seas. The Red Sea is higher than the Eastern Mediterranean, so the canal serves as a tidal strait that pours Red Sea water into the Mediterranean. The Bitter Lakes, which are hypersaline 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 equalized with that of the Red Sea, the barrier to migration was removed, and plants and animals from the Red Sea have begun to colonize 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 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 originating from the Red Sea and introduced into the Mediterranean by the construction of the canal have become a major component of the Mediterranean ecosystem and have serious impacts on the Mediterranean ecology, endangering many local and endemic Mediterranean species. Up to this day, about 300 species native to the Red Sea have already been identified in the Mediterranean Sea, and there are probably others yet unidentified. 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, facilitating the crossing of the canal for yet additional species^[8].

Pollution in this region has been extremely high in the past couple years. In just one year, 1,000,000 tons of sewage has been dumped directly into the Mediterranean Sea.^{[citation needed]} Also, many marine species, such as the Mediterranean Monk Seal, have been almost wiped out because of the pollution there. The Monk Seal has been placed as one of the top ten endangered species in the world.^{[citation needed]}

Global warming could trigger hurricanes over the Mediterranean Sea.^[9]

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References

^ entry μεσόγαιος at Liddell & Scott
^ Pinet, Paul R. (1996) Invitation to Oceanography, St Paul, MN: West Publishing Co., ISBN (3rd ed.), p.202
^ Pinet, p. 206
^ Pinet, pp. 206–7
^ Pinet, p. 207
^ IHO Codes for Oceans & Seas, and Other Code Systems Limits of Oceans and Seas, Special Publication 23, 3rd Edition 1953, published by the International Hydrographic Organization
^ Hsu K.J., "When the Mediterranean Dried Up" Scientific American, Vol. 227, December 1972, p32
^ Galil, B.S. and Zenetos, A. (2002). A sea change: exotics in the eastern Mediterranean Sea, in: Leppäkoski, E. et al. (2002). Invasive aquatic species of Europe: distribution, impacts and management. pp. 325-336.
^ Ben Hirschler (16 July 2007). Warming may bring hurricanes to Mediterranean. Reuters.

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See also

Mediterranean Basin
Mediterranean climate
Mediterranean diet
Mediterranean forests, woodlands, and shrub
Mediterranean Games
Mediterranean race
Mediterranean sea (oceanography)
Mediterranean Union
Familial Mediterranean fever
History of the Mediterranean region
Holy League (Mediterranean)
Inland Sea, which is sometimes named after the Japanese Mediterranean Sea
List of islands in the Mediterranean
Suez Canal
Babelmed, the site of the Mediterranean cultures
Piri Reis, early Mediterranean maps
Parliamentary Assembly of the Mediterranean

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External links

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Mediterranean Sea

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