Retroflection is the movement of an ocean current that doubles back on itself.
More commonly used to describe the way the mammalianintestine oruterus might turn back on itself, retroflection was first used in an oceanographic sense in 1970 by South African oceanographerNils Bang, to describe theAgulhas Current[1] which curves on itself at the southern tip of Africa to become the Aghulhas Return Current.[2] 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,[3] yet his studies using closely spacedbathythermograph readings, were later corroborated by satellite thermal imagery. The term was then revived[4] and is now common parlance among oceanographers. The Agulhas current's retroflection is now key to an understanding of its dynamics.[3]
TheNorth Brazil Current (NBC) is a westernboundary 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 theNorth Equatorial Countercurrent andNorth Equatorial Undercurrent. The NBC sheds large anticyclonic rings that move northwestward along thecontinental 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 themeridional overturning circulation (MOC).[5][6]
In the southeastAtlantic Ocean the currentretroflects (turns back on itself) in the Agulhas Retroflection due to shear interactions with the strongAntarctic Circumpolar Current. This water becomes theAgulhas Return Current, rejoining theIndian Ocean Gyre. It is estimated that up to 85 Sv (Sverdrups) of the net transport is returned to theIndian Ocean through the retroflection. The remaining water is transported into theSouth Atlantic Gyre in the Agulhas Leakage. Along with direct branch currents, this leakage takes place in surface water filaments, and Agulhas Eddies.[7]
This article incorporatespublic domain material from websites or documents of theNational Oceanic and Atmospheric Administration. This article incorporatespublic domain material from websites or documents of theNational Oceanic and Atmospheric Administration.