1.
Abyssal plain
–
An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between 3,000 metres and 6,000 metres. Lying generally between the foot of a rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth’s surface. They are among the flattest, smoothest and least explored regions on Earth, Abyssal plains are key geologic elements of oceanic basins. In addition to elements, active oceanic basins also typically include an oceanic trench. Abyssal plains were not recognized as distinct physiographic features of the sea floor until the late 1940s and, until very recently and they are poorly preserved in the sedimentary record, because they tend to be consumed by the subduction process. The creation of the plain is the end result of spreading of the seafloor. Magma rises from above the asthenosphere and as this material reaches the surface at mid-ocean ridges it forms new oceanic crust. This is constantly pulled sideways by spreading of the seafloor, Abyssal plains result from the blanketing of an originally uneven surface of oceanic crust by fine-grained sediments, mainly clay and silt. Much of this sediment is deposited by turbidity currents that have been channelled from the continental margins along submarine canyons down into deeper water, the remainder of the sediment is composed chiefly of pelagic sediments. Metallic nodules are common in areas of the plains, with varying concentrations of metals, including manganese, iron, nickel, cobalt. These nodules may provide a significant resource for future mining ventures, owing in part to their vast size, abyssal plains are currently believed to be a major reservoir of biodiversity. The abyss also exerts significant influence upon ocean carbon cycling, dissolution of calcium carbonate, the structure and function of abyssal ecosystems are strongly influenced by the rate of flux of food to the seafloor and the composition of the material that settles. Factors such as change, fishing practices, and ocean fertilization are expected to have a substantial effect on patterns of primary production in the euphotic zone. This will undoubtedly impact the flux of material to the abyss in a similar manner and thus have a profound effect on the structure, function. The ocean can be conceptualized as being divided into zones, depending on depth. Photosynthesis in turn requires energy from sunlight to drive the chemical reactions that produce organic carbon, the stratum of the water column nearest the surface of the ocean is referred to as the photic zone. The photic zone can be subdivided into two different vertical regions, the uppermost portion of the photic zone, where there is adequate light to support photosynthesis by phytoplankton and plants, is referred to as the euphotic zone. The lower portion of the zone, where the light intensity is insufficient for photosynthesis, is called the dysphotic zone
Abyssal plain
–
Tubeworms and
soft corals at a
cold seep located at 3000 meters depth on the
Florida Escarpment.
Eelpouts, a
galatheid crab, and an
alvinocarid shrimp are feeding on chemosynthetic
mytilid mussels.
Abyssal plain
–
Diagrammatic cross-section of an
oceanic basin, showing the relationship of the abyssal plain to a
continental rise and an
oceanic trench
2.
South Africa
–
South Africa, officially the Republic of South Africa, is the southernmost country in Africa. South Africa is the 25th-largest country in the world by land area and it is the southernmost country on the mainland of the Old World or the Eastern Hemisphere. About 80 percent of South Africans are of Sub-Saharan African ancestry, divided among a variety of ethnic groups speaking different Bantu languages, the remaining population consists of Africas largest communities of European, Asian, and multiracial ancestry. South Africa is a multiethnic society encompassing a variety of cultures, languages. Its pluralistic makeup is reflected in the recognition of 11 official languages. The country is one of the few in Africa never to have had a coup détat, however, the vast majority of black South Africans were not enfranchised until 1994. During the 20th century, the black majority sought to recover its rights from the dominant white minority, with this struggle playing a role in the countrys recent history. The National Party imposed apartheid in 1948, institutionalising previous racial segregation, since 1994, all ethnic and linguistic groups have held political representation in the countrys democracy, which comprises a parliamentary republic and nine provinces. South Africa is often referred to as the Rainbow Nation to describe the multicultural diversity. The World Bank classifies South Africa as an economy. Its economy is the second-largest in Africa, and the 34th-largest in the world, in terms of purchasing power parity, South Africa has the seventh-highest per capita income in Africa. However, poverty and inequality remain widespread, with about a quarter of the population unemployed, nevertheless, South Africa has been identified as a middle power in international affairs, and maintains significant regional influence. The name South Africa is derived from the geographic location at the southern tip of Africa. Upon formation the country was named the Union of South Africa in English, since 1961 the long form name in English has been the Republic of South Africa. In Dutch the country was named Republiek van Zuid-Afrika, replaced in 1983 by the Afrikaans Republiek van Suid-Afrika, since 1994 the Republic has had an official name in each of its 11 official languages. Mzansi, derived from the Xhosa noun umzantsi meaning south, is a name for South Africa. South Africa contains some of the oldest archaeological and human fossil sites in the world, extensive fossil remains have been recovered from a series of caves in Gauteng Province. The area is a UNESCO World Heritage site and has termed the Cradle of Humankind
South Africa
–
Mapungubwe Hill, the site of the former capital of the
Kingdom of Mapungubwe
South Africa
–
Flag
South Africa
–
Arrival of
Jan van Riebeeck, the first European to settle in South Africa, with
Devil's Peak in the background
South Africa
–
Depiction of a
Zulu attack on a Boer camp in February 1838
3.
Agulhas Bank
–
The Agulhas Bank is a broad, shallow part of the southern African continental shelf which extends up to 250 km south of Cape Agulhas before falling steeply to the abyssal plain. It is the region where the warm Indian Ocean and the cold Atlantic Ocean meet. This convergence leads to treacherous sailing conditions, accounting for numerous wrecked ships in the area over the years, however the meeting of the oceans here also fuels the nutrient cycle for marine life, making it one of the best fishing grounds in South Africa. The Agulhas Bank stretches approximately 800 km along the African coast, from off Cape Peninsula to Port Alfred, the bank is 50 m deep near the coast and reaches 200 m before dropping steeply to 1,000 m on its southern edge. The shelf spans an area of 116,000 km2 with a mean depth slightly over 100 m, the National Spatial Biodiversity Assessment 2004 recognised 34 biozones nested within 9 bioregions. The National Biodiversity Assessment 2011 replaced these ecozones and biozones with the terms ecoregions, in 2011, the Agulhas Ecoregion was divided into four distinct ecozones, Agulhas inshore, Agulhas inner shelf, Agulhas outer shelf, and Agulhas shelf edge. 33 different benthic habitats types were identified on the Agulhas Bank, there are dozens of warm temperate reefs along the coast of the Agulhas Ecoregion spanning from 5–30 m below sea level. Many rocky sub-tidal reefs are of aeolianite or sandstone origin, but granite, quartzite, the Agulhas reefs are very heterogeneous and include several possible different sub-types. Some of the reefs are protected areas, but only a few of those protected areas include protection from fishing. The Agulhas Bank is a boundary between ocean currents from the Atlantic Ocean, Indian Ocean, and Southern Ocean, resulting in one of the most turbulent waters of the world oceans. The Agulhas Current flows south along the African east-coast and along the edge of the bank. It then retroflects back into the Indian Ocean south-west of the bank and this retroflection results in intense eddy activities such as meanders, eddies, and filaments. In upper layer water, the Agulhas rings and eddies move warm and salty water into the large South Atlantic gyre, in the lower ocean layers water is transported in the opposite direction. Cyclonic eddies is another source of edge upwelling west of Port Elisabeth, plumes of warm surface water migrate onto the bank along its eastern edge, providing subtropical surface water from the Indian Ocean. In summer, easterly winds can intermittently drive coastal upwelling along the South African south coast, as the current is diverged away from the coast, dynamic processes draws an onshore Ekman layer of cold water from below the warm shelf-edge flow. In spring and summer, at a depth of 100 m, in summer, there is mixture of subtropical water separated by thermoclines from cool waters, but there is a considerable seasonal variation. On the shelf, bottom waters exhibit characteristics of the central Indian Ocean in the east, as the Agulhas Current flows south along the African east coast, it tends to bulge inshore frequently, a deviation from the currents normal path known as Agulhas Current meanders. These bulges are occasionally followed by a much larger offshore bulge, Natal pulses move along the coast at 20 km per day
Agulhas Bank
–
Map of the Agulhas Bank centred on the Outeniqua Basin
Agulhas Bank
–
Light blue plankton in a 150 km (93 mi) wide anti-cyclonic (counter-clockwise) Agulhas ring 800 km (500 mi) south the South Africa. Such eddies, among the largest in the world, are peeled off the Agulhas Current on the eastern edge of the Agulhas Bank.
Agulhas Bank
–
The Agulhas Bank relative to the Agulhas Ridge,
Basin, and
Plateau
Agulhas Bank
–
Papery burnupena in
False Bay
4.
Agulhas Plateau
–
The Agulhas Plateau is an oceanic plateau located in the south-western Indian Ocean about 500 km south of South Africa. The plateau formed 100 to 94 Ma together with Northeast Georgia Rise, the Agulhas Plateau is one of the key structures in the reconstruction of the Gondwana break-up. It was first mapped in 1964, but its composition, paleoposition. The boundary between the Earths crust and the mantle rises from 25 to 15 km between the Agulhas Bank and the Agulhas passage, typical for a continent-ocean transition. The Agulhas Passage consists of 120-160 Ma-old oceanic crust, whereas the 100-80 Ma-old Agulhas Plateau rises 2.5 km above the ocean floor while the Moho dips to between 20–22 km below it. The morphology of the basement below the plateau is irregular. The basement below the plateau, however, is smooth. ODP drilling at the Northeast Georgia Rise indicated that the Agulhas Plateau, some researchers, nevertheless, remained convinced that the plateau was at least partly of continental origin. Over several decades analyses of geoid, MAGSAT, gravitational, uenzelmann-Neben, Gohl & Ehrhardt 1999 finally could present seismic evidence that showed that the Agulhas Plateau was a large igneous province made entirely of oceanic crust. The Agulhas Plateau is the core of a large-scale volcanism that started in the Lazarev Sea with the emplacement of the Karoo basalts 184 Ma. This process continued with the formation of the Mozambique Ridge -Agulhas Plateau LIP which was active in phases between 140-95 Ma and this formation coincides with the formation of the Kerguelen-Heard Plateau. The MOZR formed 140-122 Ma and must have reached its maximum extent about 120 Ma while the zone between Africa and Antarctica was located under its eastern flank. The South Atlantic Ocean started to open-up 130 Ma when the Falkland Plateau moved westwards along what was becoming the Agulhas-Falkland Fracture Zone. In the wake of the Falkland Plateau, during the Cretaceous quiet interval, first the Natal Valley formed, then the Transkei Basin, the process continued with the formation of the Agulhas Plateau—Northeast Georgia Rise—Maud Rise LIP at the end of the Early Cretaceous. The AP-NEGR-MR LIP formed when the region passed over the Bouvet hotspot, about 94 Ma the main eruption ended and seafloor spreading detached the NEGR and MR from the AP. Before this separation the AP-NEGR-MR LIP consisted of 1. 2×10^6 km2 of oceanic plateau, the MOZR and AP are today connected by a crustal corridor, the Transkei Rise, which rises 500–1,000 m above the surrounding ocean floor. This rise is thought to be the product of continuous but reduced volcanism during the 20 Ma period between the formation of the MOZR-AP LIP and AP-NEGR-MR LIP. Volcanic layers on the southern Agulhas Plateau where later overlaid by sediments in which traces of either sub-areal or shallow marine erosions indicate that the plateau was near sea-level, southern Africa experienced two periods of erosion and denudation during the Early and Mid-late Cretaceous
Agulhas Plateau
–
The Agulhas Plateau is limited by the
Agulhas Passage to the north; by the
Agulhas Basin to the west; and by the Transkei Basin to the north-east.
5.
Agulhas Basin
–
The Agulhas Basin is an oceanic basin located south of South Africa where the South Atlantic Ocean and south-western Indian Ocean meet. Part of the African Plate, it is bounded by the Agulhas Ridge to the north and the Southwest Indian Ridge to the south, by the Meteor Rise to the west, a large number of bathymetric anomalies hints at the basins dynamic tectonic history. In a Late Paleocene reconstruction of the opening of the South Atlantic Ocean the Meteor Rise lies conjugate to the Islas Orcadas Rise, the separation of the Meteor Rise and the Islas Orcadas Rise marks the beginning of the formation of the Agulhas Basin. The Agulhas Ridge extends from the tip of the Meteor Rise towards the Agulhas Bank south of South Africa. The ridge, however, ends abruptly in a plateau at 40°S 15°E where it intersects a northeastward-trending spreading centre that was abandoned during the Early Paleocene. The presence of a tectonic plate between these structures was first proposed by LaBrecque & Hayes 1979. They named it the Malvinas Plate and proposed that it was active from 90 Ma until the spreading ceased in the Agulhas Basin at 65 Ma, the plate is located at a proto-Bouvet Triple Junction. Furthermore, magnetic anomalies on the Malvinas Plate do not align with their conjugates on the African Plate if the spreading rates and directions of South America and Africa are used as a guide. They also noted that the Agulhas Fracture Zone do not lay perpendicular to traces of the South America-Africa spreading north of it and cannot, the Agulhas Rift is the abandoned Malvinas-Africa ridge crest. 97 Ma the plate boundary in the Agulhas Basin was reorganised when the Mid-Atlantic Ridge made an eastward jump and this brought the boundary towards the Agulhas Plateau where excessive volcanism was building a large igneous province. The inception of the Malvinas Plate accompanied this shortening of the Agulas Fracture Zone,61 Ma, the Malvinas Plate was finally incorporated into the African Plate when the Malvinas-Africa ridge was abandoned as the result of a westward ridge jump along the Agulhas-Falkland Fracture Zone. This second ridge jump reduced one of the most spectacular fracture zones in Earths history —1,200 km in length — to 180 km, the Agulhas Current flows south along the African east coast. When it reaches the tip of Africa, it retroflects back into the Indian Ocean. At this retroflection it leakes warm core eddies known as Agulhas rings into the South Atlantic, in the Agulhas basin, half of these rings are subdivided one or several times. Antarctic Bottom Water originated in the Oligocene with the opening of the Drake Passage, AABW mixes with other masses in the Antarctic Circumpolar Current to form the Circumpolar Deep Water. In the Agulhas Basin CDW flows northward and is deflect mostly westward by the Agulhas Ridge. A branch of CDW, however, enters the Cape Basin west of the ridge from where it flows west along the side of the ridge before being deflected north-east at the eastern end of the ridge. This long detour in the Cape Basin and mixing with North Atlantic Deep Water results in water than other CDW masses
Agulhas Basin
–
The Agulhas Basin and some of the bathymetric structures mentioned in the text
6.
Indian Ocean
–
The Indian Ocean is the third largest of the worlds oceanic divisions, covering 70,560,000 km2. It is bounded by Asia on the north, on the west by Africa, on the east by Australia, the Indian Ocean is known as Ratnākara, the mine of gems in ancient Sanskrit literature, and as Hind Mahāsāgar, in Hindi. The northernmost extent of the Indian Ocean is approximately 30° north in the Persian Gulf, the oceans continental shelves are narrow, averaging 200 kilometres in width. An exception is found off Australias western coast, where the width exceeds 1,000 kilometres. The average depth of the ocean is 3,890 m and its deepest point is Diamantina Deep in Diamantina Trench, at 8,047 m deep, Sunda Trench has a depth of 7, 258–7,725 m. North of 50° south latitude, 86% of the basin is covered by pelagic sediments. The remaining 14% is layered with terrigenous sediments, glacial outwash dominates the extreme southern latitudes. The major choke points include Bab el Mandeb, Strait of Hormuz, the Lombok Strait, the Strait of Malacca, the Indian Ocean is artificially connected to the Mediterranean Sea through the Suez Canal, which is accessible via the Red Sea. All of the Indian Ocean is in the Eastern Hemisphere and the centre of the Eastern Hemisphere is in this ocean, marginal seas, gulfs, bays and straits of the Indian Ocean include, The climate north of the equator is affected by a monsoon climate. Strong north-east winds blow from October until April, from May until October south, in the Arabian Sea the violent Monsoon brings rain to the Indian subcontinent. In the southern hemisphere, the winds are milder. When the monsoon winds change, cyclones sometimes strike the shores of the Arabian Sea, the Indian Ocean is the warmest ocean in the world. Long-term ocean temperature records show a rapid, continuous warming in the Indian Ocean, Indian Ocean warming is the largest among the tropical oceans, and about 3 times faster than the warming observed in the Pacific. Research indicates that human induced greenhouse warming, and changes in the frequency, among the few large rivers flowing into the Indian Ocean are the Zambezi, Shatt al-Arab, Indus, Godavari, Krishna, Narmada, Ganges, Brahmaputra, Jubba and Irrawaddy River. The oceans currents are controlled by the monsoon. Two large gyres, one in the northern hemisphere flowing clockwise and one south of the equator moving anticlockwise, during the winter monsoon, however, currents in the north are reversed. Deep water circulation is controlled primarily by inflows from the Atlantic Ocean, the Red Sea, north of 20° south latitude the minimum surface temperature is 22 °C, exceeding 28 °C to the east. Southward of 40° south latitude, temperatures drop quickly, surface water salinity ranges from 32 to 37 parts per 1000, the highest occurring in the Arabian Sea and in a belt between southern Africa and south-western Australia
Indian Ocean
–
The economically important
Silk Road (red) and spice
trade routes (blue) were blocked by the
Ottoman Empire in ca. 1453 with the fall of the
Byzantine Empire. This spurred exploration, and a new sea route around Africa was found, triggering the
Age of Discovery.
Indian Ocean
–
Extent of the Indian Ocean according to the
CIA World Factbook
Indian Ocean
–
British heavy cruisers
Dorsetshire and
Cornwall under Japanese air attack and heavily damaged on 5 April 1942
Indian Ocean
–
A
dhow off the coast of Kenya
7.
South Atlantic Ocean
–
The Atlantic Ocean is the second largest of the worlds oceans with a total area of about 106,460,000 square kilometres. It covers approximately 20 percent of the Earths surface and about 29 percent of its surface area. It separates the Old World from the New World, the Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Eurasia and Africa to the east, and the Americas to the west. The Equatorial Counter Current subdivides it into the North Atlantic Ocean, in contrast, the term Atlantic originally referred specifically to the Atlas Mountains in Morocco and the sea off the Strait of Gibraltar and the North African coast. The Greek word thalassa has been reused by scientists for the huge Panthalassa ocean that surrounded the supercontinent Pangaea hundreds of years ago. The term Aethiopian Ocean, derived from Ancient Ethiopia, was applied to the Southern Atlantic as late as the mid-19th century, many Irish or British people refer to the United States and Canada as across the pond, and vice versa. The Black Atlantic refers to the role of ocean in shaping black peoples history. Irish migration to the US is meant when the term The Green Atlantic is used, the term Red Atlantic has been used in reference to the Marxian concept of an Atlantic working class, as well as to the Atlantic experience of indigenous Americans. Correspondingly, the extent and number of oceans and seas varies, the Atlantic Ocean is bounded on the west by North and South America. It connects to the Arctic Ocean through the Denmark Strait, Greenland Sea, Norwegian Sea, to the east, the boundaries of the ocean proper are Europe, the Strait of Gibraltar and Africa. In the southeast, the Atlantic merges into the Indian Ocean, the 20° East meridian, running south from Cape Agulhas to Antarctica defines its border. In the 1953 definition it extends south to Antarctica, while in later maps it is bounded at the 60° parallel by the Southern Ocean, the Atlantic has irregular coasts indented by numerous bays, gulfs, and seas. Including these marginal seas the coast line of the Atlantic measures 111,866 km compared to 135,663 km for the Pacific. Including its marginal seas, the Atlantic covers an area of 106,460,000 km2 or 23. 5% of the ocean and has a volume of 310,410,900 km3 or 23. 3%. Excluding its marginal seas, the Atlantic covers 81,760,000 km2 and has a volume of 305,811,900 km3, the North Atlantic covers 41,490,000 km2 and the South Atlantic 40,270,000 km2. The average depth is 3,646 m and the maximum depth, the bathymetry of the Atlantic is dominated by a submarine mountain range called the Mid-Atlantic Ridge. It runs from 87°N or 300 km south of the North Pole to the subantarctic Bouvet Island at 42°S, the MAR divides the Atlantic longitudinally into two halves, in each of which a series of basins are delimited by secondary, transverse ridges. The MAR reaches above 2000 m along most of its length, the MAR is a barrier for bottom water, but at these two transform faults deep water currents can pass from one side to the other
South Atlantic Ocean
–
The Atlantic Ocean as seen from the western coast of
Portugal
South Atlantic Ocean
–
The Atlantic Ocean, not including
Arctic and
Antarctic regions
South Atlantic Ocean
–
The Atlantic Ocean as seen from
Atlantic City, New Jersey.
South Atlantic Ocean
–
Myrtle Beach, South Carolina view of the Atlantic Ocean.
8.
Gondwana
–
In paleogeography, Gondwana, also Gondwanaland, is the name given to an ancient supercontinent. It is believed to have sutured about 600 to 530 million years ago, Gondwana formed prior to Pangaea, and later became part of it. Around 335 to 250 million years ago Gondwana and Laurasia joined together to form the supercontinent Pangaea, Gondwana then separated from Laurasia in the breakup of Pangaea, drifting farther south after the split. Gondwana itself then also broke apart, the continent of Gondwana was named by Austrian scientist Eduard Suess, after the Gondwana region of central northern India which is derived from Sanskrit for forest of the Gonds. The name had previously used in a geological context, first by H. B. From which the Gondwana sedimentary sequences are also described, for example, the plant family Proteaceae, known only from southern South America, South Africa, Australia, and New Zealand, is considered to have a Gondwanan distribution. This pattern is considered to indicate an archaic, or relict. The assembly of Gondwana was a protracted process, several orogenies led to its final amalgamation 550 to 500 million years ago at the end of the Ediacaran, and into the Cambrian. These include the Brasiliano Orogeny, the East African Orogeny, the Malagasy Orogeny, the final stages of Gondwanan assembly overlapped with the opening of the Iapetus Ocean between Laurentia and western Gondwana. During this interval, the Cambrian explosion occurred and this is the Famatinian block and it formerly continued the line of the Appalachians southwards. One of the sites of Gondwanan amalgamation was the East African Orogeny. The East African Orogeny at about 650–630 Mya affected a part of Arabia, north-eastern Africa, East Africa. Collins and Windley propose that in this orogeny, Azania collided with the Congo–Tanzania–Bangweulu Block, the later Malagasy orogeny at about 550–515 Mya affected Madagascar, eastern East Africa and southern India. In it, Neoproterozoic India collided with the already combined Azania and Congo–Tanzania–Bangweulu Block, at the same time, in the Kunga Orogeny Neoproterozoic India collided with the Australia/Mawson continent. Other large continental masses, including the core cratons of North America, Europe, when Pangaea broke up, two large masses, Gondwana and Laurasia, were formed. During the late Paleozoic, Gondwana extended from a point at or near the South Pole to near the Equator, across much of Gondwana, the climate was mild. During the Mesozoic, the world was on average warmer than it is today. Gondwana was then host to a variety of flora and fauna for many millions of years
Gondwana
–
Reconstruction showing final stages of assembly of Gondwana, 550 Mya
Gondwana
–
Map of
Pangaea with Laurasia and Gondwana. 200 mya
Gondwana
–
The
Nothofagus plant genus illustrates Gondwanan distribution, having descended from the supercontinent and existing in present-day Australia, New Zealand, New Caledonia, and the
Southern Cone. Fossils have also recently been found in Antarctica.
9.
Weddell Sea
–
The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land, the easternmost point is Cape Norvegia at Princess Martha Coast, Queen Maud Land. To the east of Cape Norvegia is the King Haakon VII Sea, much of the southern part of the sea is covered by a permanent, massive ice shelf field, the Filchner-Ronne Ice Shelf. The sea is contained within the two overlapping Antarctic territorial claims of Argentina, and Britain, and also partially within the territorial claim of Chile. At its widest the sea is around 2,000 kilometres across, various ice shelves, including the Filchner-Ronne Ice Shelf, fringe the Weddell sea. Whilst a dramatic event, the area that disappeared was far smaller than the area of ice shelf that remains. The Weddell Sea has been deemed by scientists to have the clearest water of any sea, the Ross Sea is relatively peaceful, predictable, and safe. The sea is named after the Scottish sailor James Weddell, who entered the sea in 1823 and originally named it after King George IV, also in 1823, the American sealing captain Benjamin Morrell claimed to have seen land some 10–12° east of the seas actual eastern boundary. He called this New South Greenland, but its existence was disproved when the sea was more fully explored in the early 20th century. Weddell got as far south as 74°S, the furthest southern penetration since Weddell, the Weddell Sea is an important area of deep water mass formation through cabbeling, the main driving force of the thermohaline circulation. Deep water masses are formed through cabbeling in the North Atlantic and are caused by differences in temperature. In the Weddell sea this is brought mainly by brine exclusion. In 1823, British sailor James Weddell discovered the Weddell Sea, Otto Nordenskiöld, leader of the 1901-1904 Swedish Antarctic Expedition, spent a winter at Snow Hill with a team of four men when the relief ship became beset in ice and was finally crushed. The crew managed to reach Paulet Island where they wintered in a primitive hut, Nordenskiöld and the others finally were picked up by the Argentine Navy at Hope Bay. The Antarctic Sound is named after the ship of Otto Nordenskiöld. The sound that separates the tip of the Antarctic Peninsula from Dundee Island is also named “Iceberg Alley”, Snowhill Island, located east of the Antarctic Peninsula. It is almost completely snow-capped, hence its name, Swedish Antarctic Expedition under Otto Nordenskiöld built a cabin on the island in 1902 where Nordenskiöld and three members of the expedition had to spend two winters. In 1915, Ernest Shackleton’s ship, the Endurance got trapped and was crushed by ice in this sea, after 15 months on the pack-ice Shackleton and his men managed to reach Elephant Island and finally safely returned
Weddell Sea
–
Weddell Sea as part of the
Southern Ocean
Weddell Sea
–
Scarred and chiseled sea ice in the Weddell Sea
Weddell Sea
–
Diving Weddell seals
10.
Oceanic crust
–
Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. The crust overlies the solidified and uppermost layer of the mantle, the crust and the solid mantle layer together constitute oceanic lithosphere. Oceanic crust is the result of erupted mantle material originating from below the plate, cooled and in most instances and this occurs mostly at mid-ocean ridges, but also at scattered hotspots, and also in rare but powerful occurrences known as flood basalt eruptions. It is primarily composed of rocks, or sima, which is rich in iron. Although a complete section of oceanic crust has not yet been drilled, Oceanic crust is significantly simpler than continental crust and generally can be divided in three layers. Layer 1 is on an average 0.4 km thick and it consists of unconsolidated or semiconsolidated sediments, usually thin or even not present near the mid-ocean ridges but thickens farther away from the ridge. Layer 3 is formed by slow cooling of magma beneath the surface and consists of coarse grained gabbros and it constitutes over two-thirds of oceanic crust volume with almost 5 km thickness. The most voluminous volcanic rocks of the floor are the mid-oceanic ridge basalts. These rocks have low concentrations of large ion lithophile elements, light rare earth elements, volatile elements, there can be found basalts enriched with incompatible elements, but they are rare and associated with mid-ocean ridge hot spots such as surroundings of Galapagos Islands, the Azores and Iceland. Oceanic crust is continuously being created at mid-ocean ridges, as plates diverge at these ridges, magma rises into the upper mantle and crust. As it moves away from the ridge, the lithosphere becomes cooler and denser, the youngest oceanic lithosphere is at the oceanic ridges, and it gets progressively older away from the ridges. As the mantle rises it cools and melts, as the pressure decreases, the amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness, an example of this is the Gakkel Ridge under the Arctic Ocean. Thicker than average crust is found above plumes as the mantle is hotter and hence it crosses the solidus and melts at a depth, creating more melt. An example of this is Iceland which has crust of thickness ~20 km, the oceanic lithosphere subducts at what are known as convergent boundaries. These boundaries can exist between oceanic lithosphere on one plate and oceanic lithosphere on another, or between oceanic lithosphere on one plate and continental lithosphere on another, in the second situation, the oceanic lithosphere always subducts because the continental lithosphere is less dense. The subduction process consumes older oceanic lithosphere, so oceanic crust is more than 200 million years old. The process of super-continent formation and destruction via repeated cycles of creation and destruction of oceanic crust is known as the Wilson cycle, the oldest large scale oceanic crust is in the west Pacific and north-west Atlantic - both are about up to 180-200 million years old
Oceanic crust
–
Colors indicate the age of oceanic lithosphere, wherein red indicates the youngest age, and blue indicates the oldest age. The lines represent tectonic plates.
11.
Large igneous province
–
The source of many or all LIPs is variously attributed to mantle plumes or to processes associated with plate tectonics. Types of LIPs can include large volcanic provinces, created through flood basalt, rampino and Stothers cite eleven distinct flood-basalt episodes - occurring in the past 250 million years - which created volcanic provinces and plateaus and coincided with mass extinctions. However, more flood basalts have been recognized, such as the large Ontong Java Plateau, mafic, basalt sea floors and other geological products of normal plate tectonics were not included in the definition. The definition of LIP has been expanded and refined, and is still a work in progress, LIP is now frequently also used to describe voluminous areas of, not just mafic, but all types of igneous rocks. Sub-categorization of LIPs into large volcanic provinces and large plutonic provinces, Large igneous provinces are created during short-lived igneous events resulting in relatively rapid and high-volume accumulations of volcanic and intrusive igneous rock. These events warrant study because, The study of LIPs has economic implications, some workers associate them with trapped hydrocarbons. They are associated with economic concentrations of copper–nickel and iron and they are also associated with formation of major mineral provinces including Platinum-Group Element Deposits, and in the Silicic LIPs, silver and gold deposits. Titanium and vanadium deposits are found in association with LIPs. Future LIP events may pose a hazard to human civilization, LIPs in the geological record have marked major changes in the hydrosphere and atmosphere, leading to major climate shifts and maybe mass extinctions of species. Plate tectonic theory explains topography using interactions between the plates, as influenced by viscous stresses created by flow within the underlying mantle. Since the mantle is extremely viscous, the flow rate varies in pulses which are reflected in the lithosphere by small amplitude. Understanding how the interaction between mantle flow and lithosphere elevation influences formation of LIPs is important to gaining insights into past mantle dynamics, LIPs have played a major role in continental breakup, continental formation, new crustal additions from the upper mantle, and supercontinent cycles. Earth has a shell made of a number of discrete. The mantles flow is driven by the descent of cold tectonic plates during subduction, the surface of the Earth reflects stretching, thickening and bending of the tectonic plates as they interact. In this model, tectonic plates diverge at mid-ocean ridges, where hot mantle rock flows upward to fill the space, plate-tectonic processes account for the vast majority of Earths volcanism. Beyond the effects of convectively driven motion, deep processes have other influences on the surface topography, the convective circulation drives up-wellings and down-wellings in Earths mantle that are reflected in local surface levels. Hot mantle materials rising up in a plume can spread out radially beneath the tectonic plate causing regions of uplift and these ascending plumes play an important role in LIP formation. When created, LIPs often have an extent of a few million km²
Large igneous province
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Only a few of the largest large igneous provinces are indicated (by the dark purple areas) on this geological map, which depicts crustal geologic provinces as seen in
seismic refraction data.
Large igneous province
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Three Devil's grade in
Moses Coulee, Washington is part of the
Columbia River Basalt Group LIP.
Large igneous province
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Illustration showing a vertical
dike and a horizontal sill.
12.
Agulhas Current
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The Agulhas Current /əˈɡʌləs/ is the western boundary current of the southwest Indian Ocean. It flows down the east coast of Africa from 27°S to 40°S and it is narrow, swift and strong. The sources of the Agulhas Current are the East Madagascar Current, the Mozambique Current, the net transport of the Agulhas Current is estimated as 100 Sv. The flow of the Agulhas Current is directed by the topography, the current follows the continental shelf from Maputo to the tip of the Agulhas Bank. Here the momentum of the current overcomes the vorticity balance holding the current to the topography, the current reaches its maximum transport near the Agulhas Bank where it ranges between 95-136 Sv. The core of the current is defined as where the surface velocities reaches 100 cm/s, the mean peak speed is 136 cm/s, but the current can reach 245 cm/s. As the Agulhas Current flows south along the African east coast, it tends to bulge inshore frequently and these bulges are occasionally followed by a much larger offshore bulge, known as Natal pulses. Natal pulses move along the coast at 20 km per day, an ACM can bulge up to 20 km and a NP up to 120 km from the currents mean position. The AC passes 34 km offshore and an ACM can reach 123 km offshore, when the AC meanders, its width broadens from 88 km to 125 km and its velocity weakens from 208 cm/s to 136 cm/s. An ACM induces a strong inshore counter-current, large-scale cyclonic meanders known as Natal pulses are formed as the Agulhas Current reaches the continental shelf on the South African east-coast. As these pulses moves along the coast on the Agulhas Bank, such a ring shedding can be triggered by a Natal pulse alone, but sometimes meanders on the Agulhas Return Current merge to contribute to the shedding of an Agulhas ring. This water becomes the Agulhas Return Current, rejoining the Indian Ocean Gyre and it is estimated that up to 85 Sv of the net transport is returned to the Indian Ocean through the retroflection. The remaining water is transported into the South Atlantic Gyre in the Agulhas Leakage, along with direct branch currents, this leakage takes place in surface water filaments, and Agulhas Eddies. It is estimated that as much as 15 Sv of Indian Ocean water is leaked directly into the South Atlantic,10 Sv of this is relatively warm, salty thermocline water, with the remaining 5 Sv being cold, low salinity Antarctic Intermediate Water. Since Indian Ocean water is warmer and saltier than South Atlantic water. This heat flux is believed to contribute to the rate of evaporation in the South Atlantic. It should be noted that an amount of the Agulhas Leakage joins the North Brazil Current. Surface water filaments are estimated to account for up to 13% of the total salt transport from the Agulhas Current into the Benguela Current, due to surface dissipation, these filaments are not believed to significantly contribute to inter-basin heat flux
Agulhas Current
13.
Western boundary current
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Boundary currents are ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories, western boundary currents and eastern boundary currents. Eastern boundary currents are relatively shallow, broad and slow-flowing and they are found on the eastern side of oceanic basins. Coastal upwelling often brings nutrient-rich water into eastern boundary current regions, western boundary currents are warm, deep, narrow, and fast flowing currents that form on the west side of ocean basins due to western intensification. They carry warm water from the tropics poleward, examples include the Gulf Stream, the Agulhas Current, and the Kuroshio. Western intensification is the intensification of the arm of an oceanic current. The trade winds blow westward in the tropics, and the westerlies blow eastward at mid-latitudes and this wind pattern applies a stress to the subtropical ocean surface with negative curl in the northern hemisphere and a positive curl in the southern hemisphere. The resulting Sverdrup transport is equatorward in both cases, western intensification also occurs in the polar gyres, where the sign of the wind stress curl and the direction of the resulting currents are reversed. It is because of western intensification that the currents on the boundary of a basin are stronger than those on the eastern boundary. Western intensification was first explained by the American oceanographer Henry Stommel, the wind is blowing towards the west at y =0 and towards the east at y = b. Such currents are observed to be faster, deeper, narrower and warmer than their eastern counterparts. The streamlines exhibit a behavior in all directions, with the height contours demonstrating a nearly parallel relation to the streamlines. The physics of western intensification can be understood through a mechanism that helps maintain the balance along an ocean gyre. He assumed a geostrophic flow, while neglecting any frictional or viscosity effects. Sverdrup introduced a potential vorticity argument to connect the net, interior flow of the oceans to the wind stress. This is accomplished via a decrease in planetary vorticity, a phenomenon attainable through an equator-wardly directed, the opposite is applicable when Ekman divergence is induced, leading to Ekman absorption and a subsequent, water column stretching and poleward return flow, a characteristic of sub-polar gyres. This return flow, as shown by Stommel, occurs in a meridional current, to balance the vorticity source induced by the wind stress forcing, Stommel introduced a linear frictional term in the Sverdrup equation, functioning as the vorticity sink. Walter Munk further implemented Stommels theory of western intensification by using a more realistic frictional term, Ekman Transport Ocean Gyres Sverdrup Balance Thurman, Harold V. Trujillo, Alan P. On the wind-driven ocean circulation, J. Meteorol, Ocean Currents, A Derivative of the Encyclopedia of Ocean Sciences
Western boundary current
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The main ocean currents involved with the North Pacific Gyre
14.
Agulhas Return Current
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The Agulhas Return Current is an ocean current in the South Indian Ocean. The ARC contributes to the exchange between oceans by forming a link between the South Atlantic Current and the South Indian Ocean Current. It can reach velocities of up to 4 knots and is popular among participants in trans-oceanic sailing races. The Agulhas Current follows the continental shelf of the African east-coast, pass through the Agulhas Passage until it leaves the Agulhas Bank and reaches the Agulhas Basin south of South Africa. From there it retroflects almost completely back into the south Indian Ocean as the ARC, the water mass loses a lot of heat at the Agulhas Retroflection, up to 200 W/m3, while evaporation and precipitation change the composition of the upper layers. The ARC, therefore, has another composition than the Agulhas Current proper and it also loses velocity from 110–75 cm/s and volume transport from 70 to 54 million m³/s. Furthermore, all traces of Indian Tropical Surface Water are gone, having left the retroflection, the ARC meanders east between 36°S and 41°S. These meanders were described as Rossby waves in 1970 and are known to shed cold eddies equatorward, the ARC makes a large, quasi-permanent northward meander around the Agulhas Plateau after which it loses more velocity and volume by leakage into the South Indian subtropical gyre. Over the Crozet Basin the last remnants of the ARC are gone, as it enters the Crozet Basin at 53°E, the transport of the ARC is 35 Sv, most of which is recirculated northward before reaching the Kerguelen-Amsterdam Passage. The current east of the Crozet Basin, at 66°E-70°E, is called the South Indian Ocean Current and lacks the distinctive features of the ARC
Agulhas Return Current
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The Agulhas Return Current (ARC) meanders east from the southern tip of Africa
15.
Gyre
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A gyre in oceanography is any large system of circulating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis effect, planetary vorticity along with horizontal and vertical friction, determine the circulation patterns from the wind curl. The term gyre can be used to refer to any type of vortex in the air or the sea, even one that is man-made, atlantic Equatorial Current System Pacific Equatorial Current System Indian Monsoon Gyres The center of a subtropical gyre is a high pressure zone. Circulation around the high pressure is clockwise in the hemisphere and counterclockwise in the southern hemisphere. The high pressure in the center is due to the winds on the northern side of the gyre. These cause frictional surface currents towards the latitude at the center of the gyre and this build-up of water in the center creates flow towards the equator in the upper 1,000 to 2,000 m of the ocean, through rather complex dynamics. This flow is returned towards the pole in a western boundary current. Subpolar gyres form at high latitudes, circulation of surface wind and ocean water is counterclockwise in the Northern Hemisphere, around a low-pressure area, such as the persistent Aleutian Low and the Icelandic Low. Surface currents generally move outward from the center of the system and this drives the Ekman transport, which creates an upwelling of nutrient-rich water from the lower depths. Subpolar circulation in the southern hemisphere is dominated by the Antarctic Circumpolar Current, there are minor gyres in the Weddell Sea and the Ross Sea, the Weddell Gyre and Ross Gyre, which circulate in a clockwise direction. Recently stronger winds, especially the trade winds in the Pacific ocean have provided a mechanism for vertical heat distribution. The effect are changes in the currents, increasing the subtropical overturning. Depending on natural variability, during La Niña years around 30% more heat from the upper layer is transported into the deeper ocean. Several studies in recent years, found an increase in OHC of the deep and upper ocean regions. Because the Coriolis effect is strongest near the poles, water flowing eastward at high latitudes turns sooner and is short circuiting the gyre, at the equator the Coriolis effect is nonexistent and the water flows westward until it encounters a blocking continent. Westward boundary currents are faster and deeper than eastern boundary currents. Ocean gyres are known to collect pollutants
Gyre
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The five major ocean gyres
16.
Antarctic Circumpolar Current
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The Antarctic Circumpolar Current is an ocean current that flows clockwise from west to east around Antarctica. An alternative name for the ACC is the West Wind Drift, the ACC is the dominant circulation feature of the Southern Ocean and has a mean transport of 100-150 Sverdrups, making it the largest ocean current. More recent research puts this number at over 173 Sv. The current is due to the lack of any landmass connecting with Antarctica. Associated with the Circumpolar Current is the Antarctic Convergence, where the cold Antarctic waters meet the waters of the subantarctic. These nurture high levels of phytoplankton with associated copepods and krill, and resultant foodchains supporting fish, whales, seals, penguins, albatrosses and a wealth of other species. The clipper route, which is the fastest sailing route around the world, the current creates the Ross and Weddell gyres. The ACC connects the Atlantic, Pacific and Indian Oceans, the current is strongly constrained by landform and bathymetric features. Passing through the Indian Ocean, the current first retroflects the Agulhas Current to form the Agulhas Return Current before it is split by the Kerguelen Plateau, deflection is also seen as it passes over the mid-ocean ridge in the Southeast Pacific. The current is accompanied by three fronts, the Subantarctic front, the Polar front, and the Southern ACC front, furthermore, the waters of the Southern Ocean are separated from the warmer and saltier subtropical waters by the subtropical front. The northern boundary of the ACC is defined by the edge of the SAF. Still further south lies the PF, which is marked by a transition to cold, relatively fresh. Here a temperature minimum is allowed by salinity dominating density stratification, further south still is the SACC, which is determined as the southernmost extent of Circumpolar Deep Water. This water mass flows along the shelfbreak of the western Antarctic Peninsula and thus marks the most southerly water flowing through Drake Passage, the bulk of the transport is carried in the middle two fronts. The total transport of the ACC at Drake Passage is estimated to be around 135 Sv, or about 135 times the transport of all the worlds rivers combined. There is a small addition of flow in the Indian Ocean, with the transport south of Tasmania reaching around 147 Sv. The circumpolar current is driven by the westerly winds in the latitudes of the Southern Ocean. In latitudes where there are continents, winds blowing on light surface water can pile up light water against these continents
Antarctic Circumpolar Current
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The Antarctic Circumpolar Current is the strongest current system in the world oceans and the only ocean current linking all major oceans: the Atlantic, Indian and Pacific Oceans. Seawater density fronts after Orsi, Whitworth & Nowlin 1995.
Antarctic Circumpolar Current
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The
Falkland Current transports nutrient-rich cold waters from the ACC north towards the
Brazil–Malvinas Confluence. Phytoplankton chlorophyll concentration are shown in blue (lower concentrations) and yellow (higher concentrations).
17.
Oligocene
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The Oligocene is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present. As with other geologic periods, the rock beds that define the epoch are well identified but the exact dates of the start. The name Oligocene comes from the Ancient Greek ὀλίγος and καινός, the Oligocene is preceded by the Eocene Epoch and is followed by the Miocene Epoch. The Oligocene is the third and final epoch of the Paleogene Period, the Oligocene is often considered an important time of transition, a link between the archaic world of the tropical Eocene and the more modern ecosystems of the Miocene. Major changes during the Oligocene included an expansion of grasslands. By contrast, the Oligocene–Miocene boundary is not set at an easily identified worldwide event, Oligocene faunal stages from youngest to oldest are, The Paleogene Period general temperature decline is interrupted by an Oligocene 7-million-year stepwise climate change. A deeper 8.2 °C,400, 000-year temperature depression leads the 2 °C, the stepwise climate change began 32.5 Ma and lasted through to 25.5 Ma, as depicted in the PaleoTemps chart. The Oligocene climate change was a increase in ice volume. The 7-million-year depression abruptly terminated within 1–2 million years of the La Garita Caldera eruption at 28–26 Ma, a deep 400, 000-year glaciated Oligocene Miocene boundary event is recorded at McMurdo Sound and King George Island. During this epoch, the continued to drift toward their present positions. Antarctica became more isolated and finally developed an ice cap, a brief marine incursion marks the early Oligocene in Europe. Marine fossils from the Oligocene are rare in North America, there appears to have been a land bridge in the early Oligocene between North America and Europe, since the faunas of the two regions are very similar. Sometime during the Oligocene, South America was finally detached from Antarctica and it also allowed the Antarctic Circumpolar Current to flow, rapidly cooling the Antarctic continent. Angiosperms continued their expansion throughout the world as tropical and sub-tropical forests were replaced by deciduous forests. Open plains and deserts became more common and grasses expanded from their habitat in the Eocene moving out into open tracts. However, even at the end of the period, grass was not quite enough for modern savannas. In North America, subtropical species dominated with cashews and lychee trees present, and temperate trees such as roses, beeches, the legumes spread, while sedges, bulrushes, and ferns continued their ascent. Even more open landscapes allowed animals to grow to larger sizes than they had earlier in the Paleocene epoch 30 million years earlier, marine faunas became fairly modern, as did terrestrial vertebrate fauna on the northern continents
Oligocene
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Restoration of Oligocene fauna of North America
18.
Antarctic Bottom Water
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The Antarctic bottom water is a type of water mass in the Southern Ocean surrounding Antarctica with temperatures ranging from −0.8 to 2 °C, salinities from 34.6 to 34.7 psu. Being the densest water mass of the World Ocean, AABW is found to occupy the range below 4000 m of all ocean basins that have a connection to the Southern Ocean at that level. The major significance of Antarctic bottom water is that it is the coldest bottom water, Antarctic bottom water also has a high oxygen content relative to the rest of the oceans deep waters. This is due to the oxidation of deteriorating organic content in the rest of the deep oceans, Antarctic bottom water has thus been considered the ventilation of the deep ocean. Antarctic bottom water is created in part due to the overturning of ocean water. Antarctic bottom water is formed in the Weddell and Ross Seas, off the Adélie Coast and by Cape Darnley from surface water cooling in polynyas, a unique feature of Antarctic bottom water is the cold surface wind blowing off the Antarctic continent. The surface wind creates the polynyas which opens up the surface to more wind. This Antarctic wind is stronger during the months and thus the Antarctic bottom water formation is more pronounced during the Antarctic winter season. Surface water is enriched in salt from sea ice formation, due to its increased density, it flows down the Antarctic continental margin and continues north along the bottom. It is the densest water in the ocean, and underlies other bottom. The Weddell Sea Bottom Water is the densest component of the Antarctic bottom water, upon reaching the equator, about one-third of the northward flowing Antarctic bottom water enters the Guiana Basin, mainly through the southern half of the Equatorial Channel at 35°W. The other part recirculates and some of it flows through the Romanche Fracture Zone into the eastern Atlantic, at 44°W, north of the Ceará Rise, Antarctic bottom water flows west in the interior of the basin. A large fraction of the Antarctic bottom water enters the eastern Atlantic through the Vema Fracture Zone, in the Indian Ocean the Crozet-Kerguelen Gap allows Antarctic bottom water to move toward the equator. This northward movement amounts to 2.5 Sv and it takes the Antarctic Bottom Water 23 years to reach the Crozet-Kerguelen Gap. Glossary of Physical Oceanography Steele, John H. Steve A, “Formation of Antarctic Bottom Water in the Weddell Sea, ” Journal of Geophysical Research, Vol.76, No
Antarctic Bottom Water
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AABW is formed in the Southern Ocean from surface water cooling in polynyas
19.
North Atlantic Deep Water
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North Atlantic Deep Water is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation of the oceans involves the flow of warm surface waters from the southern hemisphere into the North Atlantic. Water flowing northward becomes modified through evaporation and mixing with water masses. When this water reaches the North Atlantic it cools and sinks through convection, due to its decreased temperature, NADW is the outflow of this thick deep layer, which can be detected by its high salinity, high oxygen content, nutrient minima, and chlorofluorocarbons. CFCs are anthropogenic substances that enter the surface of the ocean from gas exchange with the atmosphere and this distinct composition allows its path to be traced as it mixes with Circumpolar Deep Water, which in turn fills the deep Indian Ocean and part of the South Pacific. NADW has a temperature of 2-4 °C with a salinity of 34. 9-35.0 psu found at a depth between 1500 and 4000m, the NADW is a complex of several water masses formed by deep convection and also by overflow of dense water across the Greenland-Iceland-Scotland Ridge. The upper layers are formed by deep open ocean convection during winter, Labrador Sea Water, formed in the Labrador Sea can reach depths of 2000 m as dense water sinks downward. Classical Labrador Sea Water production is dependent on preconditioning of water in the Labrador Sea from the year. During a positive NAO phase, conditions exist for strong winter storms to develop and these storms freshen the surface water, and their winds increase cyclonic flow, which allows denser waters to sink. As a result, the temperature, salinity, and density vary yearly, in some years these conditions do not exist and CLSW is not formed. CLSW has characteristic temperature of 3 °C, salinity of 34.88 psu. Another component of LSW is the Upper Labrador Sea Water, ULSW forms at a density lower than CLSW and has a CFC maximum between 1200 and 1500 m in the subtropical North Atlantic. Eddies of cold less saline ULSW have similar densities of warmer water and flow along the DWBC. The ULSW eddies erode rapidly as they mix laterally with this warmer saltier water, the lower waters mass of NADW form from overflow of the Greenland-Iceland-Scotland Ridge. They are Iceland-Scotland Overflow Water and Denmark Strait Overflow Water, the formation of both of these waters involves the conversion of warm salty northward flowing surface waters to cold dense deep waters behind the Greenland-Iceland-Scotland Ridge. Water flow from the North Atlantic current enters the Arctic Ocean through the Norwegian Current which splits into the Fram Strait, Water from the Fram Strait recirculates, reaching a density of DSOW, sinks, and flows towards the Denmark Strait. Water flowing into the Barent Sea feeds ISOW, ISOW enters the eastern North Atlantic over the Iceland-Scotland Ridge through the Faeroe Bank Channel at a depth of 850 m, with some water flowing over the shallower Iceland-Faeroe Rise. ISOW has a low CFC concentrations and it has been estimated from these concentrations that ISOW resides behind the ridge for 45 years and this water is less dense than and lays above it as it flows cyclonically in the Irminger Basin
North Atlantic Deep Water
–
The NADW flows southward through the Atlantic, approaching the
Antarctic Bottom Water past the
Mid-Atlantic Ridge.
North Atlantic Deep Water
–
This figure depicts circulation patterns in the North Atlantic Ocean. Cold, dense water is shown in blue, flowing south from upper latitudes, while warm, less dense water, shown in red flows north from low latitudes.
20.
Geographic coordinate system
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A geographic coordinate system is a coordinate system used in geography that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are chosen such that one of the numbers represents a vertical position. A common choice of coordinates is latitude, longitude and elevation, to specify a location on a two-dimensional map requires a map projection. The invention of a coordinate system is generally credited to Eratosthenes of Cyrene. Ptolemy credited him with the adoption of longitude and latitude. Ptolemys 2nd-century Geography used the prime meridian but measured latitude from the equator instead. Mathematical cartography resumed in Europe following Maximus Planudes recovery of Ptolemys text a little before 1300, in 1884, the United States hosted the International Meridian Conference, attended by representatives from twenty-five nations. Twenty-two of them agreed to adopt the longitude of the Royal Observatory in Greenwich, the Dominican Republic voted against the motion, while France and Brazil abstained. France adopted Greenwich Mean Time in place of local determinations by the Paris Observatory in 1911, the latitude of a point on Earths surface is the angle between the equatorial plane and the straight line that passes through that point and through the center of the Earth. Lines joining points of the same latitude trace circles on the surface of Earth called parallels, as they are parallel to the equator, the north pole is 90° N, the south pole is 90° S. The 0° parallel of latitude is designated the equator, the plane of all geographic coordinate systems. The equator divides the globe into Northern and Southern Hemispheres, the longitude of a point on Earths surface is the angle east or west of a reference meridian to another meridian that passes through that point. All meridians are halves of great ellipses, which converge at the north and south poles, the prime meridian determines the proper Eastern and Western Hemispheres, although maps often divide these hemispheres further west in order to keep the Old World on a single side. The antipodal meridian of Greenwich is both 180°W and 180°E, the combination of these two components specifies the position of any location on the surface of Earth, without consideration of altitude or depth. The grid formed by lines of latitude and longitude is known as a graticule, the origin/zero point of this system is located in the Gulf of Guinea about 625 km south of Tema, Ghana. To completely specify a location of a feature on, in, or above Earth. Earth is not a sphere, but a shape approximating a biaxial ellipsoid. It is nearly spherical, but has an equatorial bulge making the radius at the equator about 0. 3% larger than the radius measured through the poles, the shorter axis approximately coincides with the axis of rotation
Geographic coordinate system
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Longitude lines are perpendicular and latitude lines are parallel to the equator.
(PDF). Tectonophysics. 609: 675–689. doi:10.1016/j.tecto.2013.08.033. Retrieved 12 November 2016.
