Antarctic bottom water

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Antarctic bottom water in the Southern Ocean from the surface water cooling of the polynya formed

Antarctic soil water (engl .: Antarctic bottom water , AABW ) is a body of water in the Southern Ocean around the continent Antarctica with temperature ranges is between -0.8 ° to 2 ° C (35 ° F) and the salinity from 34.6 to 34.7  psu .

The Antarctic bottom water is the body of water with the greatest density in the oceans and covers a depth of around 4,000 m of all ocean basins that are connected to the South Ocean at this depth. Its main characteristic is its low temperature, which means that this body of water has a major impact on the circulation in the oceans. Bottom water also has a higher concentration of oxygen in relation to the other bodies of water in the oceans, where many decomposition processes take place. It is therefore assumed that the Antarctic bottom water also plays an important role in gas exchange (ventilation of the deep ocean).

Education and circulation

Antarctic bottom water is partly formed through violent circulation processes. It arises from surface water in the Weddell Sea ⊙ and in the Ross Sea , off Adélieland ⊙ and Cape Darnley , which cools in polynjas and under the ice shelf . The influence of the cold surface winds that fall from the Antarctic continent is unique. The wind forms the polynjas, which makes the surface water even more exposed to the wind. In winter the wind gets stronger and so more Antarctic bottom water is created in winter. Surface water has a high salinity because the sea ice leads to a concentration of the salt. Because of its higher density, it then flows along the Antarctic continental margin and on the bottom towards the north. As a body of water with a high density, it forms its own currents under the other bodies of water. Within these water masses, the Weddell Sea Bottom Water has the highest density. It flows relatively leisurely at speeds of 2–5 Sv .

Signs have been found that the formation of bottom water was not uniform over the course of the Holocene (over the past 10,000 years). that is, the formation varied due to different conditions. In addition to the presence and extent of polynjas, the calving of large glaciers also has a decisive influence on the formation of bottom water. The calving of the Mertz Glacier from December 12th to 13th February 2010 could have reduced the formation of soil water in the waters off Adélie and Georg-V.-Land by up to 23% during this period. Change of grain size (coarse vs. fine), sediment structures ( oblique stratification vs. lamination + bioturbation ) and origin of the material (presence vs. absence of glacial debris) in the Holocene sediment tradition of the Mac Robertson shelf and the shelf in front of Georg V. Land provide indications that the strength of the ground currents there, which probably correlates positively with the volume of newly formed Antarctic groundwater, has fluctuated considerably over the past millennia due to the climate.

AABW outflow in the equatorial region of the Atlantic.

Atlantic

The Vema Canal ⊙ , a deep-sea trench in the Rio Grande Ridge of the South Atlantic , is an important drain for AABW and Weddell Sea Bottom Water on their way north. As soon as the water reaches the equator , about a third of the water pours into the Guiana Basin , with most of it flowing through the southern half of the Equatorial Canal (35 ° W). The remaining water flows back and another part flows through the Romanchegraben into the East Atlantic. In the Guiana Basin, west of 40 ° W, the topography and the strong eastward flowing Deep Western Boundary Current could prevent the Antarctic bottom water from flowing westward. So it is carried further north on the eastern slope of the Ceará ridge . At 44 ° W, north of the Ceará ridge, the water flows west again into the center of the basin.

AABW drainage routes in the southern Atlantic and Ind

Indo-pacific

In the Indian Ocean , the Crozet-Kerguelen Gap allows drainage to the north. There the water flows at a speed of approx. 2.5  Sv . It takes 23 years for the water to arrive at the Crozet-Kerguelen Gap. South of Africa , the bottom water flows north through the Agulhas Basin and then eastwards through the Agulhas Passage and over the southern edges of the Agulhas Plateau , from where it flows into the Mozambique Basin .

See also

literature

  • Glossary of Physical Oceanography ( Memento of August 6, 2011 in the Internet Archive )
  • John H. Steele, Steve A. Thorpe, Karl K. Turekian (Eds.): Ocean Currents: A derivative of the Encyclopedia of Ocean Sciences. 1st edition. Academic Press, 2010, ISBN 978-0-08-096486-7 .
  • James M. Seabrooke, Gary L. Hufford, Robert B. Elder: Formation of Antarctic Bottom Water in the Weddell Sea. In: Journal of Geophysical Research. Vol. 76, no. 9, 1971, pp. 2164-2178.
  • E. Fahrbach, G. Rohardt, N. Scheele, M. Schroder, V. Strass, A. Wisotzki: Formation and discharge of deep and bottom water in the northwestern Weddell Sea. In: Journal of Maritime Research. Volume 53, No. 4, 1995, pp. 515-538.

Individual evidence

  1. ^ AMS Glossary, Antarctic Bottom Water. American Meteorological Society, accessed February 20, 2012 .
  2. ↑ Lynne Talley: Some aspects of ocean heat transport by the shallow, intermediate and deep overturning circulations . In: Geophysical Monographs . tape 112 , 1999, pp. 1-22 .
  3. ↑ R. Massom, K. Michael, PT Harris, MJ Potter: The distribution and formative processes of latent heat polynyas in East Antarctica. In: Annals of Glaciology. Volume 27, 1998, pp. 420-426.
  4. ^ WS Broecker, SL Peacock, S. Walker, R. Weiss, E. Fahrbach, M. Schroeder, U. Mikolajewicz, C. Heinze, R. Key, TH Peng, S. Rubin: How much deep water is formed in the Southern Ocean? In: Journal of Geophysical Research. Volume 103, No. C8, 1998, pp. 15833-15843.
  5. ↑ K. Kusahara, H. Hasumi, GD Williams: Impact of the Mertz Glacier Tongue calving on dense water formation and export. In: Nature Communications. 2, 2011, art. no. 159, doi: 10.1038 / ncomms1156 .
  6. ↑ PT Harris: Ripple cross-laminated sediments on the East Antarctic shelf: evidence for episodic bottom water production during the Holocene? In: Marine Geology. Volume 170, 2000, pp. 317-330.
  7. ↑ PT Harris, G. Brancolini, L. Armand, M. Busetti, RJ Beaman, G. Giorgetti, M. Prestie, F. Trincardi: Continental shelf drift deposit indicates non-steady state Antarctic bottom water production in the Holocene. In: Marine Geology. Volume 179, 2001, pp. 1-8.
  8. ↑ AMS Glossary, Vema Channel ( Memento from July 1, 2012 in the web archive archive.today ) American Meteorological Society
  9. ^ Monika Rhein, Lothar Stramma, Gerd Krahmann: The spreading of Antarctic bottom water in the tropical Atlantic . In: Deep-Sea Research Part I . tape 45 , 1998, pp. 507-527 , doi : 10.1016 / S0967-0637 (97) 00030-7 , bibcode : 1998DSRI ... 45..507R .
  10. ^ TWN Haine, AJ Watson, MI Liddicoat, RR Dickson: The flow of Antarctic bottom water to the southwest Indian Ocean estimated using CFCs . In: Journal of Geophysical Research . tape 103 , 1998, pp. 27637 , doi : 10.1029 / 98JC02476 , bibcode : 1998JGR ... 10327637H .
  11. ↑ G. Uenzelmann-Neben, K. Huhn: Sedimentary deposits on the southern South African continental margin: Slumping versus non-deposition or erosion by oceanic currents? In: Marine Geology . tape 266 , 2009, p. 65–79 , doi : 10.1016 / j.margeo.2009.07.011 .