1.
South Atlantic Gyre
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The South Atlantic Gyre is the subtropical gyre in the south Atlantic Ocean. In the southern portion of the gyre, northwesterly winds drive eastward-flowing currents that are difficult to distinguish from the boundary of the Antarctic Circumpolar Current. Like other oceanic gyres, it collects vast amounts of floating debris, South of this gyre is the Antarctic Circumpolar Current. This current flows from West to East around Antarctica, another name for this current is the West Wind Drift. This current allows Antarctica to maintain its huge ice sheet by keeping warm ocean waters away, at approximately 125 Sv, this current is the largest ocean current. The Brazil Current is the western boundary current of the gyre and it flows south along the Brazilian coast to the Rio de la Plata. The current is considerably weaker than its North Atlantic counterpart, the Gulf Stream, Ocean current Volta do mar Ocean currents Ocean currents
2.
Ocean current
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Depth contours, shoreline configurations, and interactions with other currents influence a currents direction and strength. Therefore ocean currents are primarily horizontal water movements, Ocean currents flow for great distances, and together, create the global conveyor belt which plays a dominant role in determining the climate of many of the Earth’s regions. More specifically, ocean currents influence the temperature of the regions through which they travel, for example, warm currents traveling along more temperate coasts increase the temperature of the area by warming the sea breezes that blow over them. Perhaps the most striking example is the Gulf Stream, which makes northwest Europe much more temperate than any region at the same latitude. Another example is Lima, Peru where the climate is cooler than the tropical latitudes in which the area is located, in these wind driven currents, the Ekman spiral effect results in the currents flowing at an angle to the driving winds. In addition, the areas of ocean currents move somewhat with the seasons. Deep ocean basins generally have a surface current, in that the eastern equatorward-flowing branch is broad. These western boundary currents are a consequence of the rotation of the Earth, Deep ocean currents are driven by density and temperature gradients. Thermohaline circulation is known as the oceans conveyor belt. These currents, called submarine rivers, flow under the surface of the ocean and are hidden from immediate detection, where significant vertical movement of ocean currents is observed, this is known as upwelling and downwelling. Deep ocean currents are currently being researched using a fleet of robots called Argo. The South Equatorial Currents of the Atlantic and Pacific straddle the equator, though the Coriolis effect is weak near the equator, water moving in the currents on either side of the equator is deflected slightly poleward and replaced by deeper water. Thus, equatorial upwelling occurs in these westward flowing equatorial surface currents, upwelling is an important process because this water from within and below the pycnocline is often rich in nutrients and greatly benefits the growth of marine organisms. By contrast, generally poor conditions for growth prevail in most of the tropical ocean because strong layering isolates deep. Ocean currents are measured in sverdrup, where 1 sv is equivalent to a flow rate of 1,000,000 m3 per second. Surface currents are found on the surface of an ocean, and are driven by large scale wind currents and they are directly affected by the wind—the Coriolis effect plays a role in their behaviors. Horizontal and vertical currents also exist below the pycnocline in the deeper waters. The movement of water due to differences in density as a function of water temperature, ripple marks in sediments, scour lines, and the erosion of rocky outcrops on deep-ocean floors are evidence that relatively strong, localized bottom currents exist
3.
Atlantic Ocean
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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
4.
Ocean 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
5.
Cape Point
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Table Mountain and the city of Cape Town are close to the northern extremity of the same peninsula. The cape is located at 34°21′26″S 18°29′51″E, about 2.3 kilometres east, the peak above Cape Point is higher than that above the Cape of Good Hope. The rugged sandstone ridge that rises from Cape Point at sea level develops into two peaks, there is a major peak that dominates the skyline locally but there is also a smaller peak about 100 m further south. The higher peak has the old lighthouse on the top, from the end of the railway a second path leads to the lower peak. Secondly, foggy conditions often prevail at the levels, making the older lighthouse invisible to shipping. On 18 April 1911, the Portuguese liner Lusitania was wrecked just south of Cape Point at 34°23′22″S 18°29′23″E on Bellows Rock for precisely this reason, prompting the relocation of the lighthouse. The new lighthouse, located at 34°21′26″S 18°29′49″E, cannot be seen from the West until ships are at a distance to the South. The light of the new Cape Point lighthouse is the most powerful on the South African coast, with a range of 63 miles, Cape Point is situated within the Table Mountain National Park, within a section of the park referred to as Cape of Good Hope. This section covers the whole of the tip of the Cape Peninsula. The Cape of Good Hope section of the park is generally wild, the vegetation at Cape Point consists primarily of Peninsula Sandstone Fynbos. Cape Point is often claimed to be the place where the cold Benguela Current of the Atlantic Ocean. In fact, the meeting point fluctuates along the southern and southwestern Cape coast, the two intermingling currents help to create the micro-climate of Cape Town and its environs. Contrary to popular mythology, the point of the currents produces no obvious visual effect. There are, however, strong and dangerous swells, tides and localized currents around the point and these troubled seas have witnessed countless maritime disasters in the centuries since ships first sailed here. Fishing is good along the coast but the unpredictable swells make angling from the very dangerous. Over the years scores of fishermen have been swept to their deaths from the platforms by freak waves. False Bay, which opens to the east and north of Cape Point, is the location of the naval port of Simons Town. The bay is also famous - or infamous - for its great white sharks, Cape Point is the site of one of the Global Atmosphere Watchs atmospheric research stations
6.
Angola
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Angola /æŋˈɡoʊlə/, officially the Republic of Angola, is a country in Southern Africa. It is the seventh-largest country in Africa and is bordered by Namibia to the south, the Democratic Republic of the Congo to the north, Zambia to the east, and the Atlantic Ocean to west. The exclave province of Cabinda has borders with the Republic of the Congo, the capital and largest city of Angola is Luanda. In the 19th century, European settlers slowly and hesitantly began to themselves in the interior. As a Portuguese colony, Angola did not encompass its present borders until the early 20th century, following resistance by groups such as the Cuamato, the Kwanyama and the Mbunda. Independence was achieved in 1975 under a communist one-party state backed by the Soviet Union, however, the country soon descended into an even lengthier civil war that lasted until 2002. It has since become a relatively stable presidential republic. Angola has vast mineral and petroleum reserves, and its economy is among the fastest growing in the world, Angolas economic growth is highly uneven, with the majority of the nations wealth concentrated in a disproportionately small sector of the population. Angola is a state of the United Nations, OPEC, African Union, the Community of Portuguese Language Countries, the Latin Union. A highly multiethnic country, Angolas 25.8 million people span various tribal groups, customs, Angolan culture reflects centuries of Portuguese rule, namely in the predominance of the Portuguese language and the Catholic Church, combined with diverse indigenous influences. The name Angola comes from the Portuguese colonial name Reino de Angola, the toponym was derived by the Portuguese from the title ngola held by the kings of Ndongo. Ndongo was a kingdom in the highlands, between the Kwanza and Lukala Rivers, nominally tributary to the king of Kongo but which was seeking greater independence during the 16th century, modern Angola was populated predominantly by nomadic Khoi and San prior to the first Bantu migrations. The Khoi and San peoples were neither pastoralists nor cultivators, following a hunter-gatherer lifestyle and they were displaced by Bantu peoples arriving from the north, some of whom likely originated in northwestern Nigeria. Bantu speakers introduced the cultivation of bananas and taro, as well as large herds, to Angolas central highlands. During this time, the Bantu established a number of entities in most of what today comprises Angola. To its south lay the Kingdom of Ndongo, from which the area of the later Portuguese colony was known as Dongo. The region now known as Angola was reached by the Portuguese explorer Diogo Cão in 1484, the year before, the Portuguese had established relations with the Kongo, which stretched at the time from modern Gabon in the north to the Kwanza River in the south. The Portuguese established their primary trading post at Soyo, which is now the northernmost city in Angola apart from the Cabinda exclave
7.
Benguela
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Benguela is a city in western Angola, south of Luanda, and capital of Benguela Province. It lies on a bay of the name, in 12° 33’ S. 13° 25’ E. Benguela is one of Angolas most populous cities. Benguela, a Portuguese fort from 1587, was founded in 1617 by the Portuguese under Manuel Cerveira Pereira and it was long the centre of an important trade, especially in slaves to Brazil and Cuba. Ships anchored about 1.6 kilometres off the shore, in depths of 7 to 11 metres, however the nearby deep-water sheltered harbour of Lobito was a much larger port. Besides the churches of S. Felipe and S. António, the hospital, a short way beyond Benguela is Baía Farta, where salt was manufactured and sulphur was extracted. Close to Baia Farta was the beach of Baia Azul, the city prospered and grew in the following decades. Starting in the early 20th century, Benguela attracted, developed, sisal and fishing industries expanded and the financial, construction and services market boomed until 1974. In 1975, after the April 1974 Carnation Revolution in Lisbon, Portugal, in the mid-2000s, with a more peaceful environment, restoration of the railway between Benguela and Huambo commenced. In 1983 Benguela had a population of 155,000, during the civil war the city of Benguela increased its population due to refugees from the countryside. While the colonial part of the city consists of relatively good-quality houses, Benguela was one of the centres of Portuguese trade to the African interior. The city remains an important commercial link between western and eastern Angola, coffee, corn, sisal, sugarcane, and tobacco are grown in the interior regions of Angola and widely traded in Benguela. Manganese from the interior is also traded in Benguela, industries local to the city include fish processing and the milling of sugarcane, the city also produces pottery, soap, and tools. Foreign trade is handled through the port of Lobito, which is located 29 kilometres north of Benguela. Lobito, once the busiest port in Angola, was disrupted during the Angolan Civil War. The port has since revived and supports trade in the Benguela region, the city formerly had a German school, Deutsche Schule Benguela. Leila Lopes - actress and Miss Universe 2011 Benguela Airport Benguela Railway Port of Lobito
8.
Upwelling
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The nutrient-rich upwelled water stimulates the growth and reproduction of primary producers such as phytoplankton. Due to the biomass of phytoplankton and presence of water in these regions, upwelling zones can be identified by cool sea surface temperatures. The increased availability in upwelling regions results in levels of primary productivity. Approximately 25% of the global marine fish catches come from five upwellings that occupy only 5% of the total ocean area. Upwellings that are driven by coastal currents or diverging open ocean have the greatest impact on nutrient-enriched waters, the three main drivers that work together to cause upwelling are wind, Coriolis effects, and Ekman transport. They operate differently for different types of upwelling, but the effects are the same. In the overall process of upwelling, winds blow across the sea surface at a particular direction, as a result of the wind, the water is transported a net of 90 degrees from the direction of the wind due to Coriolis forces and Ekman transport. This results in a spiral of water movement down the water column, then, it is the Coriolis forces that dictate which way the water will move, in the Northern hemisphere, the water is transported to the right of the direction of the wind. In the Southern Hemisphere, the water is transported to the left of the wind, if this net movement of water is divergent, then upwelling of deep water occurs to replace the water that was lost. The major upwellings in the ocean are associated with the divergence of currents that bring deeper, colder, coastal upwelling is the best known type of upwelling, and the most closely related to human activities as it supports some of the most productive fisheries in the world. Wind-driven currents are diverted to the right of the winds in the Northern Hemisphere, the result is a net movement of surface water at right angles to the direction of the wind, known as the Ekman transport. When Ekman transport is occurring away from the coast, surface waters moving away are replaced by deeper, colder, and denser water. Normally, this process occurs at a rate of about 5–10 meters per day. Deep waters are rich in nutrients, including nitrate, phosphate and silicic acid, Upwelling regions therefore result in very high levels of primary production in comparison to other areas of the ocean. They account for about 50% of global marine productivity, high primary production propagates up the food chain because phytoplankton are at the base of the oceanic food chain. All of these currents support major fisheries, the four major eastern boundary currents in which coastal upwelling primarily occurs are the Canary Current, Benguela Current, California Current, and Humboldt Current. The Benguela Current is the boundary of the South Atlantic subtropical gyre. The subsystems are divided by an area of permanent upwelling off of Luderitz, the California Current System is an eastern boundary current of the North Pacific that is also characterized by a north and south split
9.
Indian Ocean
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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
10.
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
