Retroflect
Encyclopedia
Retroflect, meaning "to turn back on itself", is an oceanographic term used to describe the movement of an ocean current which doubles back on itself.
or uterus
might turn back on itself but was first used in an oceanographic sense in 1970 by South African oceanographer Nils Bang
, to describe the Agulhas Current
which curves on itself at the southern tip of Africa to become the Aghulhas Return Current. Bang credited the inspiration for the metaphor to his wife, a nursing sister, who mentioned the term during her midwifery studies. Bang's research, through the University of Cape Town, was done on a limited budget and with rudimentary equipment, yet his studies using closely spaced bathythermograph
readings, were later corroborated by satellite thermal imagery. The term was then revived and is now common parlance among oceanographers. The Agulhas current's retroflection is now key to an understanding of its dynamics.
(NBC) is a western boundary current
that flows off the coast of northeast Brazil, in the tropical Atlantic that transports upper ocean waters across the equator. It retroflects between 4°N and 10°N. Particularly during summer and fall, the NBC retroflects from the coast at 6° to 7°N and feeds the North Equatorial Countercurrent
and North Equatorial Undercurrent. The NBC sheds large anticyclonic rings that move northwestward along the continental break. (Didden and Schott, 1993). These warm rings could play an important role in the net meridional transport of warm water in the upper layers of the Atlantic Ocean as part of the meridional overturning circulation (MOC).
In the southeast Atlantic Ocean
the current retroflects (turns back on itself) in the Agulhas Retroflection due to shear interactions with the strong Antarctic Circumpolar Current
. This water becomes the Agulhas Return Current, rejoining the Indian Ocean Gyre
. It is estimated that up to 85 Sv (Sverdrup
s) 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.
Usage history
It was more commonly used to describe the way the mammalian intestineIntestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
or uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
might turn back on itself but was first used in an oceanographic sense in 1970 by South African oceanographer Nils Bang
Nils Bang
Nils Daniel Bang was a South African oceanographic scientist who was considered a pioneer in the study of coastal upwelling systems...
, to describe the Agulhas Current
Agulhas Current
The Agulhas Current is the Western Boundary Current of the southwest Indian Ocean. It flows down the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong...
which curves on itself at the southern tip of Africa to become the Aghulhas Return Current. Bang credited the inspiration for the metaphor to his wife, a nursing sister, who mentioned the term during her midwifery studies. Bang's research, through the University of Cape Town, was done on a limited budget and with rudimentary equipment, yet his studies using closely spaced bathythermograph
Bathythermograph
The bathythermograph, or BT, is a small torpedo-shaped device that holds a temperature sensor and a transducer to detect changes in water temperature versus depth. Lowered into the water from an underway ship, the BT records pressure and temperature changes as it is dropped through the water...
readings, were later corroborated by satellite thermal imagery. The term was then revived and is now common parlance among oceanographers. The Agulhas current's retroflection is now key to an understanding of its dynamics.
Retroflection regions
The North Brazil CurrentNorth Brazil Current
North Brazil Currents is a term of the complexion of Atlantic Southern equatorial current and the Atlantic equatorial counter current, Guinea current. These stream in opposite directions, and fluctuate in their strength, thus making it very difficult to sail fast in the respective area.- See also...
(NBC) is a western boundary current
Boundary current
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:...
that flows off the coast of northeast Brazil, in the tropical Atlantic that transports upper ocean waters across the equator. It retroflects between 4°N and 10°N. Particularly during summer and fall, the NBC retroflects from the coast at 6° to 7°N and feeds the North Equatorial Countercurrent
Equatorial Counter Current
The Equatorial Counter Current is a significant ocean current in the Pacific and Indian oceans that flows west-to-east at approximately five degrees north. The Counter Currents result from balancing the west flow of water in each ocean by the North and South Equatorial currents...
and North Equatorial Undercurrent. The NBC sheds large anticyclonic rings that move northwestward along the continental break. (Didden and Schott, 1993). These warm rings could play an important role in the net meridional transport of warm water in the upper layers of the Atlantic Ocean as part of the meridional overturning circulation (MOC).
In the southeast Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
the current retroflects (turns back on itself) in the Agulhas Retroflection due to shear interactions with the strong Antarctic Circumpolar Current
Antarctic Circumpolar Current
The Antarctic Circumpolar Current is an ocean current that flows 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, at approximately 125 Sverdrups, the largest ocean current...
. This water becomes the Agulhas Return Current, rejoining the Indian Ocean Gyre
Indian Ocean Gyre
The Indian Ocean Gyre, located in the Indian Ocean, is one of the five major oceanic gyres.- External links:*...
. It is estimated that up to 85 Sv (Sverdrup
Sverdrup
The sverdrup, named in honour of the pioneering oceanographer Harald Sverdrup, is a unit of measure of volume transport. It is used almost exclusively in oceanography, to measure the transport of ocean currents. Its symbol is Sv. Note that the sverdrup is not an SI unit, and that its symbol...
s) of the net transport is returned to the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
through the retroflection. The remaining water is transported into the South Atlantic Gyre
South Atlantic Gyre
The South Atlantic Gyre is the southern branch of the subtropical gyre in the south Atlantic. This gyre is heavily influenced by northwesterly winds that drive a broad eastward drift, which makes it difficult to distinguish between the northern boundary of the subtropical gyre and the southern...
in the Agulhas Leakage. Along with direct branch currents, this leakage takes place in surface water filaments, and Agulhas Eddies.