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59-532: There are regular ferries between Sicily and Tunis across the Strait of Sicily; a tunnel has been proposed to link the two regions. Deep currents in the strait flow from east to west, and the current nearer the surface travels from west to east. This unusual water flow is of interest to oceanographers . Within the Central Mediterranean sea it is one of the topographically complex regions. With

118-656: A length of 600 km it connects the Eastern and Western Mediterranean basins. The strait is delimited by two systems; at the eastern side it is connected with the Ionian Sea , south of the Malta Bank with a sill of 560 m deep, and, on the western side, two passages connect the strait with the Western Mediterranean basin. The passage or channel more closely to Sicily is narrow and around 430 m deep while

177-678: A potential seawater density, σ θ, of around 29.10) water than the LIW. In the Ionian Sea it fills the transitional layer between the Eastern Mediterranean Deep Water and the LIW. This dense water exits the strait at a depth of 300 m at the sill and sinks down, because of its higher density than the LIW, till 1800 m when reaching the Tyrrhenian Sea flowing along the Sicilian slope. This sharp sinking down of

236-537: A southward displacement of Intertropical Convergence Zone . Changes in precipitation under high-emissions scenarios would be far larger. Additionally, the main controlling pattern of the extratropical Southern Hemisphere's climate is the Southern Annular Mode (SAM), which has been spending more and more years in its positive phase due to climate change (as well as the aftermath of ozone depletion ), which means more warming and more precipitation over

295-630: Is known as overturning . In the Pacific Ocean, the rest of the cold and salty water from the Atlantic undergoes haline forcing, and becomes warmer and fresher more quickly. The out-flowing undersea of cold and salty water makes the sea level of the Atlantic slightly lower than the Pacific and salinity or halinity of water at the Atlantic higher than the Pacific. This generates a large but slow flow of warmer and fresher upper ocean water from

354-626: Is a stub . You can help Misplaced Pages by expanding it . This European road or road transport-related article is a stub . You can help Misplaced Pages by expanding it . This tunnel-related article is a stub . You can help Misplaced Pages by expanding it . Thermohaline circulation Thermohaline circulation ( THC ) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes . The adjective thermohaline derives from thermo- referring to temperature and -haline referring to salt content , factors which together determine

413-753: Is a proposed megaproject to link Sicily and Tunisia . The distance between the coastlines is about 155 kilometres (96 miles) and would be reached by five tunnels constructed between four intermediate artificial islands which will be built with the excavated material. A preliminary study was promoted by the ENEA institute. The connections across the Strait of Sicily , as of 2011 , are by car ferry and air travel. There are ferries Palermo–Tunis (3 round trips per week), Trapani–Tunis (1 round trip per week), Civitavecchia–Tunis (2 per week), Genoa–Tunis, and Marseille–Tunis. This African road or road transport-related article

472-559: Is characterized by high salinity and temperature. This high salinity concentrations is one of the important factors for the formation of the deep water in the Southern Adriatic and the Gulf of Lions . During the past years (measured from 1993 till 1998) the potential temperature and salinity of the LIW have decreased significantly. This change in thermohaline properties of the LIW is in agreement with another event that occurred in

531-676: Is denser than the NADW, and so flows beneath it. AABW formed in the Weddell Sea will mainly fill the Atlantic and Indian Basins, whereas the AABW formed in the Ross Sea will flow towards the Pacific Ocean. At the Indian Ocean, a vertical exchange of a lower layer of cold and salty water from the Atlantic and the warmer and fresher upper ocean water from the tropical Pacific occurs, in what

590-572: Is driven by, at one site, the fresh waters entering from the Gibraltar Strait and on the other side, the negative freshwater budget from the Mediterranean Basin . Also the westward LIW in the intermediate layer and less saltier eastward Atlantic water on top are considered in this scale. The outflow of dense-water-masses characteristics of the Strait of Sicily are not stable but have been found to change interannually. Also

649-444: Is left behind as the sea ice forms around it (pure water preferentially being frozen). Increasing salinity lowers the freezing point of seawater, so cold liquid brine is formed in inclusions within a honeycomb of ice. The brine progressively melts the ice just beneath it, eventually dripping out of the ice matrix and sinking. This process is known as brine rejection . The resulting Antarctic bottom water sinks and flows north and east. It

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708-603: Is outweighed by evaporation , in part due to high windiness. When water evaporates, it leaves salt behind, and so the surface waters of the North Atlantic are particularly salty. North Atlantic is also an already cool region, and evaporative cooling reduces water temperature even further. Thus, this water sinks downward in the Norwegian Sea , fills the Arctic Ocean Basin and spills southwards through

767-423: Is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt, coined by climate scientist Wallace Smith Broecker . It is also referred to as the meridional overturning circulation, or MOC . This name is used because not every circulation pattern caused by temperature and salinity gradients is necessarily part of a single global circulation. Further, it is difficult to separate

826-582: Is the major perturbation of the circulation and water mass aspects in this area since systematic observational data is available (1950s). The effect of the EMT on the Strait of Sicily was a freshening of the surface waters. Another important circulation mechanism that exists in the Strait of Sicily is the Biomodal Oscillating System (BiOS) Which is a feedback mechanism between the Ionic and

885-700: Is the sub-basin scale with scales of 200 km till 300 km. This scale represents two dense water veins; the Atlantic Tunisian Current (ATC) which flows along the African coast and the Atlantic Ionian Stream (AIS) along the Sicilian coast. The AIS flows mainly eastward which can create upwelling on the Adventure Bank (AB) and the southern Sicilian coast. Upwelling is found to be the most intense during summer when

944-605: Is thus geometrically quite stable. The Central Mediterranean can be characterized by looking at differences in spatial and temporal scale. Three scales are common to use among oceanographers. The first is the mesoscale with a horizontal scale around ten kilometers and periods of days till a maximum of ten days. The sea can be influenced within the mesoscale by wind stress , topography and by internal dynamical processes. Boundary currents and jets can be created by these processes which can evolve into vortices and filament patterns that can interact with large scale flows. The second

1003-530: The Coralliidae ( Anthozoa , Gorgonacea ) is between a few meters to 120 meters deep. Its bright red calcific axis has been used for jewelry from ancient times. Although extinction of these corals is not the case yet because of high productivity in this ecosystem, a decline has been observed in the shallow waters. These corrals are part of an initiative of worldwide conservation. During the Conference of

1062-453: The convection of heat could drive deeper currents. In 1908, Johan Sandström performed a series of experiments at a Bornö Marine Research Station which proved that the currents driven by thermal energy transfer exist, but require that "heating occurs at a greater depth than cooling". Normally, the opposite occurs, because ocean water is heated from above by the Sun and becomes less dense, so

1121-541: The density of sea water . Wind-driven surface currents (such as the Gulf Stream ) travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water ). This dense water then flows into the ocean basins . While the bulk of it upwells in the Southern Ocean , the oldest waters (with a transit time of about 1000 years) upwell in

1180-560: The 1990s which is the uplifting of the colder and less saline deep waters in the Eastern Mediterranean referred as the Eastern Mediterranean Transient (EMT). Pantelleria is an Italian island located in the Strait of Sicily around 64 km from Tunisia. Nowadays the island is one of the destinations migrants, mostly from Tunisia, try to reach. Sometimes over 200 people in only two days cross

1239-526: The 21st century and that there was a "high confidence" changes to it would be reversible within centuries if warming was reversed. Unlike the Fifth Assessment Report, it had only "medium confidence" rather than "high confidence" in the AMOC avoiding a collapse before the end of the 21st century. This reduction in confidence was likely influenced by several review studies that draw attention to

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1298-467: The 21st century. A key reason for the uncertainty is the poor and inconsistent representation of ocean stratification in even the CMIP6 models – the most advanced generation available as of early 2020s. Furthermore, the largest long-term role in the state of the circulation is played by Antarctic meltwater, and Antarctic ice loss had been the least-certain aspect of future sea level rise projections for

1357-462: The AIS is also relatively stronger than in other seasons. Due to the upwelling these coasts are of great interests of fishery. The ATC shows a specific path in winter while the route is less clearly-marked during summer. The last common used scale is the large Mediterranean Basin scale which includes the thermohaline circulation . The thermohaline circulation in the Strait of Sicily is anti- estuarine and

1416-740: The Adriatic and therefore has great impact on the organisms within this sea and in the strait. Through the strait of Sicily passes the Levantine Intermediate Water (LIW). The LIW is a westward flowing water mass in the intermediate layers (from 200 m till 400 m) formed in the Levantine basin , the most eastern part of the Mediterranean sea and ending in the strait of Gibraltar and the Atlantic Ocean . The LIW

1475-602: The Adriatic sea. The thermohaline properties of the Adriatic Sea show quasi-decadal oscillations that are related to the circulation of the Ionian Sea. The upper-layer of the northern Ionian Sea shows circulations that vary between a cyclonic movement, corresponding advection of waters from the Eastern Mediterranean with very saline waters and low nutrients ( oligotrophic water), and anticyclonic movement which results in saline and copiotroph (nutrient-rich) waters from

1534-605: The Adventure Plateau, Graham and Nameless Banks. In 1831 a submarine volcano erupted on the Graham Bank at a depth of around 200 m, forming the Graham Island , 65 m above sea level. The island was claimed by Britain, France, and Sicily, with the potential for hostilities, but it had been washed away by December 1831. (In November 2000 Sicilians planted a flag on the underwater volcano to claim

1593-720: The Earth's radiation budget . Large influxes of low-density meltwater from Lake Agassiz and deglaciation in North America are thought to have led to a shifting of deep water formation and subsidence in the extreme North Atlantic and caused the climate period in Europe known as the Younger Dryas . In 2021, the IPCC Sixth Assessment Report again said the AMOC is "very likely" to decline within

1652-609: The Greenland-Scotland-Ridge – crevasses in the submarine sills that connect Greenland , Iceland and Great Britain. It cannot flow towards the Pacific Ocean due to the narrow shallows of the Bering Strait , but it does slowly flow into the deep abyssal plains of the south Atlantic. In the Southern Ocean , strong katabatic winds blowing from the Antarctic continent onto the ice shelves will blow

1711-530: The IPCC, the most-likely effects of future AMOC decline are reduced precipitation in mid-latitudes, changing patterns of strong precipitation in the tropics and Europe, and strengthening storms that follow the North Atlantic track. In 2020, research found a weakened AMOC would slow the decline in Arctic sea ice . and result in atmospheric trends similar to those that likely occurred during the Younger Dryas , such as

1770-505: The LIW has lower velocities and the dense water flow returns to the geostrophic position located naturally along the Sicilian coast. Here the dense water sinks into the deeper ocean sea, around 1500 m–1850 m. This inversion of the interface slope is possible because the buoyancy and Coriolis forces are balancing each other in a so-called 'geostrophic balance' which is possible because of the flow velocities of both LIW and EMDW. The tEMDW shows little variations in height, width and path and

1829-497: The Modified Atlantic Water (MAW). Underneath this eastward flow, the Levantine Intermediate Water (LIW) flows in westward direction. Just above the bottom of the Strait a relative small flow has been observed. This vein follows the same route as LIW but consists of different characteristics. The water flow is named 'transitional Eastern Mediterranean Deep Water' (tEMDW) and contains fresher, colder and denser (with

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1888-466: The North Atlantic, by the UK-US RAPID programme. It combines direct estimates of ocean transport using current meters and subsea cable measurements with estimates of the geostrophic current from temperature and salinity measurements to provide continuous, full-depth, basin-wide estimates of the meridional overturning circulation. However, it has only been operating since 2004, which is too short when

1947-572: The North Pacific, using as evidence the high values of silicon found in these waters. Other investigators have not found such clear evidence. Computer models of ocean circulation increasingly place most of the deep upwelling in the Southern Ocean, associated with the strong winds in the open latitudes between South America and Antarctica. Direct estimates of the strength of the thermohaline circulation have also been made at 26.5°N in

2006-466: The North Pacific. Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system . The water in these circuits transport both energy (in the form of heat) and mass (dissolved solids and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth. The thermohaline circulation

2065-533: The Parties of CITES number 14 (CoP14) two workshops were decided to be organized about the corals in the Pacific and Mediterranean. Among the species that are fished at high rates, are the Cephalopod family. These molluscans , especially the species O. Vulgaris, are of interest both for industrial and artisanal fisheries. Due to high biodiversity, productivity rates and importance of the different species for

2124-413: The Western Mediterranean towards the Adriatic. The density of the dense waters that flow from the Adriatic Sea into the northern Ionian Sea highly depends on the type of circulation (cyclonic, or anticyclonic) in the Ionian Sea and at the other hand influences the vorticity in the Ionian Sea itself resulting in a feedback mechanism. BiOS is one of the dominant mechanisms influencing biochemical processes in

2183-446: The channel at the side of Tunisia is broader and shallower with a maximum depth of 365 m. Due to this particular bathymetry with two different channels, the strait is called a "two-sill strait". In the central region the strait is around 50 km to 100 km wide and 700 m to 900 m deep, but some parts consist of trenches of even 1800 m deep. At the surface and in the upper 200 m the strait consists of an eastward flow provided by

2242-405: The circulation stability bias within general circulation models , and simplified ocean-modelling studies suggesting the AMOC may be more vulnerable to abrupt change than larger-scale models suggest. As of 2024 , there is no consensus on whether a consistent slowing of the AMOC circulation has occurred but there is little doubt it will occur in the event of continued climate change. According to

2301-408: The circulation, which was established in 1960 by Henry Stommel and Arnold B. Arons. They have chemical, temperature and isotopic ratio signatures (such as Pa / Th ratios) which can be traced, their flow rate calculated, and their age determined. NADW is formed because North Atlantic is a rare place in the ocean where precipitation , which adds fresh water to the ocean and so reduces its salinity,

2360-497: The climate system . The hemisphere which experiences the collapse of its circulation would experience less precipitation and become drier, while the other hemisphere would become wetter. Marine ecosystems are also likely to receive fewer nutrients and experience greater ocean deoxygenation . In the Northern Hemisphere, AMOC's collapse would also substantially lower the temperatures in many European countries, while

2419-548: The dense water flow is a topic of interest among oceanographers . A second topic of interest regarding this little tEMDW flow is that it crosses the midline of the strait, more precisely the Malta sill. When the dense water flow reaches the western sill, it flows along the Tunisian coast instead of the Sicilian shelf. The water mass flows at a shallow depth of 300 m, while beneath the LIW, the tEMDW flows westward. Further downstream,

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2478-411: The east coast of North America would experience accelerated sea level rise . The collapse of either circulation is generally believed to be more than a century away and may only occur under high warming, but there is a lot of uncertainty about these projections. It has long been known that wind can drive ocean currents, but only at the surface. In the 19th century, some oceanographers suggested that

2537-549: The ecosystem, the Mediterranean Sea and the Strait of Sicily are becoming of more interest for researchers during the recent years. Also regarding the current climate change , information can be gained by researching the changes in biodiversity in the Strait of Sicily. Due to the natural position of the Strait of Sicily, above the conjunction of the Eurasian and African tectonic plate, volcanic activity occurs in

2596-485: The freezing point. That freezing point is also lower than for fresh water due to salinity, and can be below −2 °C, depending on salinity and pressure. These density differences caused by temperature and salinity ultimately separate ocean water into distinct water masses , such as the North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW). These two waters are the main drivers of

2655-598: The high ecological importance of the strait. Warm temperature and tropical species from the Lavantin basin cross the strait. The vast variety in species cannot only be found near the surface and coasts but also the deep water contains communities of vulnerable species as the Scleractinia , Antipatharians , gorgonians and red corals . The habitat of one of the corals in the strait, the Corallium rubrum , family of

2714-544: The human population lives in the Northern Hemisphere , the AMOC has been far better studied, but both are very important for the global climate. Both of them also appear to be slowing down due to climate change , as the melting of the ice sheets dilutes salty flows such as the Antarctic bottom water . Either one could outright collapse to a much weaker state, which would be an example of tipping points in

2773-475: The island if it resurfaced.) In the year 1863 this volcano also erupted. As of 2023 the most recent eruption in the region was in 1891, around 5 km north of Pantelleria. At the southeast of Graham Bank, at the Pinne Bank an emission was observed in 1941. In 2023 three further underwater volcanoes, possibly active, were discovered off Sicily. Strait of Sicily Tunnel The Strait of Sicily Tunnel

2832-502: The newly formed sea ice away, opening polynyas in locations such as Weddell and Ross Seas , off the Adélie Coast and by Cape Darnley . The ocean, no longer protected by sea ice, suffers a brutal and strong cooling (see polynya ). Meanwhile, sea ice starts reforming, so the surface waters also get saltier, hence very dense. In fact, the formation of sea ice contributes to an increase in surface seawater salinity; saltier brine

2891-477: The ocean due to stronger westerlies , freshening the Southern Ocean further. Climate models currently disagree on whether the Southern Ocean circulation would continue to respond to changes in SAM the way it does now, or if it will eventually adjust to them. As of early 2020s, their best, limited-confidence estimate is that the lower cell would continue to weaken, while the upper cell may strengthen by around 20% over

2950-460: The ocean floor, providing a continuous thermohaline circulation. As the deep waters sink into the ocean basins, they displace the older deep-water masses, which gradually become less dense due to continued ocean mixing. Thus, some water is rising, in what is known as upwelling . Its speeds are very slow even compared to the movement of the bottom water masses. It is therefore difficult to measure where upwelling occurs using current speeds, given all

3009-408: The other wind-driven processes going on in the surface ocean. Deep waters have their own chemical signature, formed from the breakdown of particulate matter falling into them over the course of their long journey at depth. A number of scientists have tried to use these tracers to infer where the upwelling occurs. Wallace Broecker , using box models, has asserted that the bulk of deep upwelling occurs in

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3068-421: The parts of the circulation driven by temperature and salinity alone from those driven by other factors, such as the wind and tidal forces . This global circulation has two major limbs - Atlantic meridional overturning circulation ( AMOC ), centered in the north Atlantic Ocean, and Southern Ocean overturning circulation or Southern Ocean meridional circulation ( SMOC ), around Antarctica . Because 90% of

3127-462: The role of salinity in ocean layer formation. Salinity is important because like temperature, it affects water density . Water becomes less dense as its temperature increases and the distance between its molecules expands, but more dense as the salinity increases, since there is a larger mass of salts dissolved within that water. Further, while fresh water is at its most dense at 4 °C, seawater only gets denser as it cools, up until it reaches

3186-465: The strait in little boats. The winds that are found above the Strait of Sicily are the two Mediterranean winds: Sirocco , bringing dry and warm air from the South East and Mistral , bringing cold air from the northwest. The Strait of Sicily is rich in biodiversity due to its different water currents. Also its geographical  position between the Eastern and Western Mediterranean contributes to

3245-491: The strait. Volcanic activity is mainly focused on the islands Pantelleria and Linosa . A climax in volcanic activity was found in the Pleistocene . Minor submarine eruptions still occur, mostly on the seafloor along the northwest and southeast regional faults. During historical times some seamounts erupted, and other seamounts have been covered by Pliocene-Quaternary sediments. The submarine volcanoes are located in

3304-411: The surface layer floats on the surface above the cooler, denser layers, resulting in ocean stratification . However, wind and tides cause mixing between these water layers, with diapycnal mixing caused by tidal currents being one example. This mixing is what enables the convection between ocean layers, and thus, deep water currents. In the 1920s, Sandström's framework was expanded by accounting for

3363-624: The thermohaline circulation showed changes in structure and stratification . These changes were caused by deep water formed in the Aegean Sea which replaced the water formed in the Adriatic during the 1990s. This dense water caused enhanced salinity and temperatures in the Aegean Sea for a few years creating the deep/mediate Mediterranean overturning perturbation which has been given the name of Eastern Mediterranean Transient (EMT). The EMT

3422-414: The timescale of the circulation is measured in centuries. The thermohaline circulation plays an important role in supplying heat to the polar regions, and thus in regulating the amount of sea ice in these regions, although poleward heat transport outside the tropics is considerably larger in the atmosphere than in the ocean. Changes in the thermohaline circulation are thought to have significant impacts on

3481-540: The tropical Pacific to the Indian Ocean through the Indonesian Archipelago to replace the cold and salty Antarctic Bottom Water . This is also known as 'haline forcing' (net high latitude freshwater gain and low latitude evaporation). This warmer, fresher water from the Pacific flows up through the South Atlantic to Greenland , where it cools off and undergoes evaporative cooling and sinks to

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