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The Antarctic bottom water (AABW) is a type of water mass in the Southern Ocean surrounding Antarctica with temperatures ranging from 0 to -0.8 °C, salinities from 34.6 to 34.7 psu. The major significance of AABW is that it is the coldest bottom water, giving it a significant influence on the movement of the world's oceans. The potential temperature of the AABW is less than 0 °C. AABW also has a high oxygen content given by the oxidation of deteriorating organic content in the deep ocean and has been considered the "ventilation of the deep ocean."[citation needed] Compared to other water masses, AABW is characteristically cold and fresh.
Formation and circulation
[edit]Antarctic bottom water is created in part due to the major overturning of ocean water.
Antarctic bottom water is formed in the Weddell and Ross Seas from surface water cooling in polynyas and below the ice shelf. A unique feature of AABW is the cold surface wind blowing off the Antartic continent. The surface wind creates the polynyas which opens up the water surface to more wind. This Antarctic wind is stronger during the winter months and thus the AABW is more pronounced during the Antarctic winter season. Surface water is enriched in salt from sea ice formation. Due to its increased density, the water is flowing down the Antarctic continental margin and on the bottom further north. It is the densest water in the free ocean and is overlain by the waters of the Antarctic Circumpolar Current (AACW) at a depth of 1000 to 2000 m and overlies Weddell Sea bottom water (WSBW) in some locations.
About one-third of the northward flowing AABW enters the Guiana Basin, mainly through the southern half of the Equatorial Channel at 35°W. The other part recirculates and some of it flows through the Romanche Fracture Zone into the eastern Atlantic. In the Guiana Basin, west of 40°W, the sloping topography and the strong, eastward flowing deep western boundary current might prevent the AABW from flowing west: thus it has to turn north at the eastern slope of the Ceara Rise. At 44°W, north of the Ceara Rise, AABW flows west in the interior of the basin. A large fraction of the AABW enters the eastern Atlantic through the Vema Fracture Zone. On the Indian Ocean side, AABW cannot reach the northern waters due to the various deep basins of the Indian Ocean topography. There is a gap called the Crozet-Kerguelen Gap that allows AABW to move equatorward in the Indian Ocean. This equatorward movement amounts to 2.5 Sv per year.
References
[edit]
- Glossary of Physical Oceanography
- Steele, John H., Steve A. Thorpe and Karl K. Turekian, editors, Ocean Currents: A derivative of the Encyclopedia of Ocean Sciences, Academic Press, 1st ed., 2010 ISBN 978-0080964867
- Seabrooke, James M., Hufford, Gary L., and Elder, Robert B., “Formation of Antarctic Bottom Water in the Weddell Sea,” Journal of Geophysical Research, Vol. 76, No. 9, pp. 2164-2178, 1971
- Fahrbach, E., G. Rohardt, N. Scheele, M. Schroder, V. Strass, and A. Wisotzki, “Formation and discharge of deep and bottom water in the northwestern Weddell Sea”, Journal of Maritime Research, 53(4), pp. 515-538, 1995
Category:Environment of Antarctica
Category:Water masses
Category:Geology of the Southern Ocean
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