The Walvis Ridge ( walvis means whale in Dutch and Afrikaans ) is an aseismic ocean ridge in the southern Atlantic Ocean . More than 3,000 km (1,900 mi) in length, it extends from the Mid-Atlantic Ridge , near Tristan da Cunha and the Gough Islands , to the African coast (at 18°S in northern Namibia ). The Walvis Ridge is one of few examples of a hotspot seamount chain that links a flood basalt province to an active hotspot. It is also considered one of the most important hotspot tracks because the Tristan Hotspot is one of few primary or deep mantle hotspots.
26-805: Apart from the Mid-Atlantic Ridge, the Walvis Ridge and the Rio Grande Rise are the most distinctive feature of the South Atlantic sea floor. They originated from hotspot volcanism and together they form a mirrored symmetry across the Mid-Atlantic Ridge, with the Tristan Hotspot at its centre. Two of the distinct sections in the Walvis Ridge have similar mirrored regions in the Rio Grande Rise; for example,
52-669: A new unit of water flow, "the inflow through Bering Strait is one sverdrup". At the Arctic Basin Symposium in October 1962, the unit came into general usage. The water transport in the Gulf Stream gradually increases from 30 Sv in the Florida Current to a maximum of 150 Sv south of Newfoundland at 55° W longitude . The Antarctic Circumpolar Current , at approximately 125 Sv ,
78-499: A volume of one million cubic meters may be imagined as a "slice" of ocean with dimensions 1 km × 1 km × 1 m (width × length × thickness). At this scale, these units can be more easily compared in terms of width of the current (several km), depth (hundreds of meters), and current speed (as meters per second ). Thus, a hypothetical current 50 km wide, 500 m (0.5 km) deep, and moving at 2 m/s would be transporting 50 Sv of water. The sverdrup
104-399: Is composed of western and eastern areas, which have different geological backgrounds. The western area has numerous guyots and seamounts and a basement dated to 80 to 87 million years ago . The eastern area is covered by fracture zones and may represent an abandoned spreading centre. In the western area, volcanic breccia and layers of ash indicate widespread volcanism during
130-514: Is distinct from the SI sievert unit or the non-SI svedberg unit. All three use the same symbol, but they are not related. The sverdrup is named in honor of the Norwegian oceanographer, meteorologist and polar explorer Harald Ulrik Sverdrup (1888–1957), who wrote the 1942 volume The Oceans, Their Physics, Chemistry, and General Biology together with Martin W. Johnson and Richard H. Fleming. In
156-453: Is equivalent to the SI derived unit cubic hectometer per second (symbol: hm /s or hm ⋅s ): 1 Sv is equal to 1 hm /s. It is used almost exclusively in oceanography to measure the volumetric rate of transport of ocean currents . It is named after Harald Sverdrup . One sverdrup is about five times what is carried by the world's largest river, the Amazon. In the context of ocean currents ,
182-591: The Eocene , which coincides with the formation of volcanic rocks onshore. During this period, parts of the western plateau were uplifted over sea level and short-lived volcanic islands formed. When West Gondwana (i.e. South America) broke away from Africa during the Early Cretaceous ( 146 to 100 Ma ), the South Atlantic opened up from its southern to its northern end. In this process,
208-766: The Paleocene–Eocene Thermal Maximum . This period manifests as a carbonate-poor red clay layer unique to the Walvis Ridge and is similar to the PETM, but of smaller magnitude. The Walvis Ridge is a natural obstacle for the Agulhas rings , mesoscale warm core rings that are shed from the Agulhas Current south of the Agulhas Bank . In average, five such rings are shed each year, a number that varies considerably between years. The rings tend cross
234-579: The 1950s and early 1960s both Soviet and North American scientists contemplated the damming of the Bering Strait , thus enabling temperate Atlantic water to heat up the cold Arctic Sea and, the theory went, making Siberia and northern Canada more habitable. As part of the North American team, Canadian oceanographer Maxwell Dunbar found it "very cumbersome" to repeatedly reference millions of cubic meters per second. He casually suggested that as
260-547: The American side. This process resulted in the Tristan-Gough seamount chains on either side of the Tristan-Gough hotspot. A Brazilian-Japanese expedition in 2013 recovered in situ granitic and metamorphic rocks on the Rio Grande Rise. This can possibly indicate that the plateau includes fragments of continental crust — possible remains of micro-continents similar to those found on and around Kerguelen in
286-773: The Atlantic during the Tertiary ( 66 to 2.58 Ma ). At the beginning of the Maastrichtian, the characteristics of water masses differed north and south of the Rio Grande Rice-Walvis Ridge complex. The disappearance of these differences during the Maastritchtian indicates a reorganisation of oceanic circulation patterns that lead to a global homogenisation of intermediate and deep waters. This process seems to have been triggered by
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#1732765552123312-721: The Cape Basin and flows into the Indian Ocean. 26°S 6°E / 26°S 6°E / -26; 6 Rio Grande Rise The Rio Grande Rise , also called the Rio Grande Elevation or Bromley Plateau , is an aseismic ocean ridge in the southern Atlantic Ocean off the coast of Brazil . Together with the Walvis Ridge off Africa, the Rio Grande Rise forms a V-shaped structure of mirrored hotspot tracks or seamount chains across
338-493: The Indian Ocean and Jan Mayen in the Arctic Ocean. The existence of such microcontinents is speculative, however, since their remains tend to be covered by younger layers of lava and sediments. Nevertheless, transoceanic dispersals are hinted at by the fossil record of, for example, flightless birds such as Lavocatavis , indicating that several islands between Africa and South America made island hopping possible across
364-660: The Indian Ocean to the South Atlantic. Originating around Antarctica, Antarctic Bottom Water (AABW) enters the Cape Basin between the Agulhas Bank and the Agulhas Ridge after which it flows west north of the Agulhas Ridge. AABW then retroflects at the south-western end of the Walvis Ridge, flows north-east along the ridge before being retroflected south by North Atlantic Deep Water , with which it exits
390-536: The Rio Grande Rise had been breached by this time, allowing cold, dense water to move north-south through a corridor enhancing the transition from a latitudinal thermospheric circulation to a meridional thermohaline circulation . 31°S 35°W / 31°S 35°W / -31; -35 Sverdrup In oceanography , the sverdrup (symbol: Sv ) is a non- SI metric unit of volumetric flow rate , with 1 Sv equal to 1 million cubic metres per second (264,172,052 US gal/s). It
416-462: The Walvis Ridge at its deepest part, but they still lose transitional speed and many rings decay rapidly. Their transitional speed drops from 5.2±3.6 km/day to 4.6±3.1 km/day, but it is not clear how much the Walvis Ridge is responsible for this drop, since the rings' speed drops to 4.3±2.2 km/day between the Walvis Ridge and the Mid-Atlantic Ridge. The rings can cross the South Atlantic in 2.5–3 years but only two thirds make it farther than
442-584: The Walvis Ridge. When the rings pass over the Cap Basin south of the Walvis Ridge they are frequently disturbed by the Benguela Current , interaction between rings, and bottom topography such as the Vema Seamount , but there are fewer obstacles and disturbances west of the Walvis Ridge were the rings tend stabilise. The Agulhas rings transport an estimated 1-5 Sv (millions m/s) of water from
468-639: The breaching of the Rio Grande Rise-Walvis Ridge complex and the disappearance of epicontinental seaways such as the Tethys Ocean . The process resulted in the deterioration of rudist -dominated tropical habitats and consequently the extinction of benthic inoceramid bivalves. The origin of modern circulation of cold, deep water — known as the "Big Flush" — is associated with Early Eocene ( 55 to 40 Ma ) geological events; tectonism that resulted in
494-559: The central Democratic Republic of Congo and Angola align with the Walvis Ridge. The Tristan-Gough hotspot track first formed over the mantle plume that formed the Etendeka-Paraná continental flood basalts some 135 to 132 Ma . The eastern section of the ridge is thought to have been created in the Middle Cretaceous period, between 120 to 80 Ma . While the mantle plume remained large and stable,
520-549: The eastern Walvis Ridge formed along with the Rio Grande Rise over the Mid-Atlantic Ridge. During the Maastrichtian 60 million years ago , the orientation of spreading changed, which is still visible in the orientation of the various sections of the Walvis Ridge. The mantle plume then gradually became unstable and bifurcated 60 to 70 Ma to produce the two separate Tristan and Gough hotspot tracks. It finally disintegrated 35 to 45 Ma and formed
546-530: The eastern end of the Rio Grande Rise. The formation of this mirrored structure is the result of the opening of the South Atlantic some 120 Mya and the Paraná and Etendeka continental flood basalts , the lateral-most parts of the structure, formed at the beginning of this process in areas that are now located in Brazil and Namibia . The Walvis Ridge is divided into three main sections: Cretaceous kimberlites in
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#1732765552123572-525: The eastern section of the Walvis Ridge evolved in conjunction with the Torres Arch (the western end of the Rio Grande Rise, off the Brazilian coast) and, as the South Atlantic gradually opened, these structures became separated. The complex of seamounts in the western end of the Walvis Ridge, however, does not have a similar structure on the American side, but there is a Zapiola Seamount Complex south of
598-522: The guyot province in the western end of the ridge. Hundreds of volcanic explosions were recorded on the Walvis Ridge in 2001 and 2002. These explosions seemed to come from an unnamed seamount on the northern side of the ridge and are thought to be unrelated to the Tristan hotspot. The Ewing Seamount is part of the ridge. The Eocene Layer of Mysterious Origin (Elmo) is a period of global warming that occurred 53.7 Ma , about two million years after
624-474: The northern South Atlantic . In 2013, Brazilian scientists announced that they found granite boulders on the Rio Grande Rise and speculated that it could be the remains of a submerged continent, which they called the "Brazilian Atlantis". Other researchers, however, noted that such boulders can end-up on the ocean floor by less speculative means. The Rio Grande Rise separates the Santos and Campos Basins and
650-649: The opening of the north-east Atlantic and fracture zones that developed in the subsiding Rio Grande Rise, which allowed cold water from the Antarctic Weddell Sea to flow northward into the North Atlantic. 40 Ma , the generation of cold bottom water in the Antarctic resulted in the formation of psychrospheric fauna, which today live in temperatures below 10 °C (50 °F), in the Atlantic and Tethys. This global distribution suggests that
676-649: The voluminous Paraná and Etendeka continental flood basalts formed in what is now Brazil and Namibia . This event is linked to the Tristan-Gough hotspot , now located near the Mid-Atlantic Ridge , close to Tristan da Cunha and the Gough Islands . During the Maastrichtian ( 60 Ma ), the orientation of spreading changed, which is still visible on the African side, and volcanism ended on
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