Oceans and seas

Antarctic Convergence

June 11, 2012, 3:54 pm
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Antarctic Convergence. Source: Philippe Rekacewicz, UNEP/GRID-Arendal

The Antarctic Convergence, also known as the Polar Front, is an irregular line encircling Antarctica where the cold, northward-flowing Antarctic waters sink beneath the relatively warmer waters of the sub-Antarctic. This line demarcates the locus where cold, northward-flowing Antarctic current seawaters encounter the somwhat warmer waters of the subantarctic seas. Antarctic waters generally sink below subantarctic waters, while associated upwelling and mixing zones form a sea region extremely high in marine productivity, especially in relation to Antarctic krill. An alternative (and origninal name for this boundary line is the Antarctic Polar Frontal Zone (APFZ), a  concept originated in the 1960s following a detailed study of the Polar Front. This was subsequently transformed into the concept of the Polar Frontal Zone.

caption Antarctic Convergence . Source: Michigan State University

The line is actually a zone approximately 20 to 30 miles wide, varying somewhat in latitude in different longitudes, extending across the Atlantic, Pacific, and Indian Oceans between the 48th and 61st parallels of south latitude. It reaches south of 60 degrees south near New Zealand and near 48 degrees south in the far South Atlantic coinciding with the path of the maximum velocity westerly winds.

The precise location at any given place and time is made evident by the sudden change in surface temperature, which averages 5 to 10 degrees Fahrenheit (2.8 to 5.5 Celsius).

Although this zone is a mobile one, it usually does not stray more than a half a degree of latitude from its mean position. This line, like the tree line of the north, is a natural boundary rather than one derived from reasoning.

The hydrologic trasition that occurs at the convergence is shown in the diagram below. The easterly flowing Antarctic Circumpolar Current (ACC) moves the Antarctic Surface Water at the surface south of the Convergence. At the Convergence and north of it, the Antarctic Surface Water sinks to become Antarctic Intermediate Water under warmer Subantarctic Surface Water. caption Schematic diagram of sea currents and depth zones in the Antarctic region.

The Antarctic Convergence not only separates two hydrological regions, but also separates areas of distinctive marine life associations and of different climates. The term Polar Front is used because it marks the transition between the Polar Frontal Zone (PFZ) to the north and the Antarctic Zone (AZ) to the south. 

The South Shetland Islands, South Orkney Islands, South Sandwich Islands, South Georgia, Bouvetoya, Heard Island and McDonald Islands all lie south of the Antarctic Convergence. The Iles Kerguelen lie approximately on the Antarctic Convergence; the Falkland Islands, Prince Edward Islands, Iles Crozet and Macquarie Island lie north of the Antarctic Convergence.

caption The Antarctic Convergence marked against an image of ice cover on the Southern Ocean during the southern winter. NASA/National Snow and Ice Data Center

Further Reading

  • Physical Oceanography Index
  • Below the Convergence: Voyages Towards Antarctica, 1699-1839, Alan Gurney, W.W. Norton and Company, 1997 ISBN: 0393039498.
  • Matthias Tomczak and J. Stuart Godfrey. Regional Oceanography: An Introduction. Pergamon, 1994, pp. 76-79.
  • The Antarctic convergence, ICAIR ; GRID-Christchurch, New-Zealand. 
  • A. L. Gordon. Antarctic Polar Frontal Zone. In J. L. Reid, editor, Antarctic Oceanology I, number 15 in Antarct. Res. Ser., pages 205–221. AGU, 1971.
  • A. L. Gordon. Antarctic oceanographic zonation. In M. J. Dunbar, editor, Polar Oceans, pages 45–76. Arct. Inst. of North Am., 1977.
  • Igor M. Belkin and Arnold L. Gordon. Southern Ocean fronts from the Greenwich meridian to Tasmania. J. Geophys. Res., pages 3675–3696, 1996.

See Also

Glossary

Citation

Survey, U. (2012). Antarctic Convergence. Retrieved from http://www.eoearth.org/view/article/150096

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