Retroflection is the movement of an ocean current that doubles back on itself.

Usage history

More commonly used to describe the way the mammalian

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans ...

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...

might turn back on itself, retroflection was first used in an oceanographic sense in 1970 by South African oceanographer

Nils Bang Nils Daniel Bang (13 September 1941 – 2 December 1977) was a South African oceanographic scientist who was a pioneer in the study of the fine structure of coastal upwelling systems. In March 1969, Bang initiated, planned and executed South Afric ...

, to describe the

Agulhas Current The Agulhas Current () is the western boundary current of the southwest Indian Ocean. It flows south along the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong. It is suggested that it is the largest western boundary curren ...

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, Alison Coombe Bang, 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,Sciendaba, Vol XII No 48, 15 December 1977 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.

Retroflection regions

The

North Brazil Current The North Brazil Current (NBC) is a warm water ocean current that is part of the southwestern North Atlantic Gyre. It begins when the westward moving Atlantic South Equatorial Current splits in half and flows northwestward, following the coastline ...

(NBC) is a western

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 Eastern boundary currents are ...

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 Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective ''thermohaline'' derives from '' thermo-'' referring to tem ...

(MOC). * * In the southeast

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

the current ''retroflects'' (turns back on itself) in the Agulhas Retroflection due to shear interactions with the strong

Antarctic Circumpolar Current The Antarctic Circumpolar Current (ACC) is an ocean current that flows clockwise (as seen from the South Pole) from west to east around Antarctica. An alternative name for the ACC is the West Wind Drift. The ACC is the dominant circulation feat ...

. This water becomes the

Agulhas Return Current The Agulhas Return Current (ARC) is an ocean current in the South Indian Ocean. The ARC contributes to the water exchange between oceans by forming a link between the South Atlantic Current and the South Indian Ocean Current. It can reach veloc ...

, rejoining the

Indian Ocean Gyre The Indian Ocean gyre, located in the Indian Ocean, is one of the five major oceanic gyres, large systems of rotating ocean currents, which together form the backbone of the global conveyor belt. The Indian Ocean gyre is composed of two major curr ...

. It is estimated that up to 85 Sv (

Sverdrup In oceanography, the sverdrup (symbol: Sv) is a non- SI metric unit of volumetric flow rate, with equal to . It is equivalent to the SI derived unit cubic hectometer per second (symbol: hm3/s or hm3⋅s−1): 1 Sv is equal to 1 hm3/s. It is used ...

s) of the net transport is returned to the

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by th ...

through the retroflection. The remaining water is transported into the

South Atlantic Gyre The South Atlantic Gyre is the subtropical gyre in the south Atlantic Ocean. In the southern portion of the gyre, northwesterly (or southeastward-flowing) winds drive eastward-flowing currents that are difficult to distinguish from the northern ...

in the Agulhas Leakage. Along with direct branch currents, this leakage takes place in surface water filaments, and Agulhas Eddies.This paragraph is copied from the section entitled ''Retroflection'' in the Wikipedia article entitled

. This for attribution only and it is not considered a reliable source.

References

{{Reflist Oceans Ocean currents Wikipedia articles incorporating text from NOAA