First oceanographic survey of the entire continental shelf adjacent to the northern Agulhas Current
- Lutjeharms, Johan R E, Durgadoo, Jonathan V, Schapira, Mathilde, McQuaid, Christopher D
- Authors: Lutjeharms, Johan R E , Durgadoo, Jonathan V , Schapira, Mathilde , McQuaid, Christopher D
- Date: 2010
- Language: English
- Type: Article
- Identifier: vital:6867 , http://hdl.handle.net/10962/d1011499 , http://www.sajs.co.za/index.php/SAJS/article/view/410
- Description: [from introduction] The Agulhas Current is by far the largest western boundary current of the southern hemisphere1 and carries about 70 × 106 m3/s of seawater past the eastern shores of South Africa.2 Being more than 2000 m deep, it follows the continental shelf edge quite closely. Its northern part, all the way downstream to Algoa Bay, has a very stable trajectory whereas the southern part meanders widely to either side of a mean geographical location,3 in the process creating shear edge eddies and attendant plumes of warm surface water over the shelf.4 However, the direct influence of the Agulhas Current on the waters and ecosystems of the adjacent shelf of South Africa remains largely unknown.
- Full Text:
- Date Issued: 2010
- Authors: Lutjeharms, Johan R E , Durgadoo, Jonathan V , Schapira, Mathilde , McQuaid, Christopher D
- Date: 2010
- Language: English
- Type: Article
- Identifier: vital:6867 , http://hdl.handle.net/10962/d1011499 , http://www.sajs.co.za/index.php/SAJS/article/view/410
- Description: [from introduction] The Agulhas Current is by far the largest western boundary current of the southern hemisphere1 and carries about 70 × 106 m3/s of seawater past the eastern shores of South Africa.2 Being more than 2000 m deep, it follows the continental shelf edge quite closely. Its northern part, all the way downstream to Algoa Bay, has a very stable trajectory whereas the southern part meanders widely to either side of a mean geographical location,3 in the process creating shear edge eddies and attendant plumes of warm surface water over the shelf.4 However, the direct influence of the Agulhas Current on the waters and ecosystems of the adjacent shelf of South Africa remains largely unknown.
- Full Text:
- Date Issued: 2010
Physical and biological coupling in eddies in the lee of the South-West Indian Ridge
- Ansorge, Isabelle J, Pakhomov, Evgeny A, Kaehler, Sven, Lutjeharms, Johan R E, Durgadoo, Jonathan V
- Authors: Ansorge, Isabelle J , Pakhomov, Evgeny A , Kaehler, Sven , Lutjeharms, Johan R E , Durgadoo, Jonathan V
- Date: 2010
- Language: English
- Type: Article
- Identifier: vital:6493 , http://hdl.handle.net/10962/d1004477
- Description: Eddies have some decisive functions in the dynamics of the Southern Ocean ecosystems. This is particularly true in the Indian sector of the Southern Ocean, where a region of unusually high-mesoscale variability has been observed in the vicinity of the South-West Indian Ridge. In April 2003, three eddies were studied: eddy A, a recently spawned anticyclone south of the Antarctic Polar Front (APF),; eddy B, an anticyclone north of lying between the Subantarctic Front and the APF; and eddy C, a cyclone north of the APF west of the ridge. Elevated concentrations of total Chl-a coincided with the edges of the cyclonic eddy, whereas both anticyclonic eddies A and B were characterised by low total Chl-a concentrations. Biologically, the two anticyclonic eddies A and B were distinctly different in their biogeographic origin. The zooplankton community in the larger anticyclonic eddy A was similar in composition to the Antarctic Polar Frontal Zone (APFZ) community with an addition of some Antarctic species suggesting an origin just north of the APF. In contrast, the species composition within the second anticyclonic eddy B appeared to be more typical of the transitional nature of the APFZ, comprising species of both subantarctic and subtropical origin and thus influenced by intrusions of water masses from both north and south of the Subantarctic Front. Back-tracking of these features shows that the biological composition clearly demarcates the hydrographic origin of these features.
- Full Text:
- Date Issued: 2010
- Authors: Ansorge, Isabelle J , Pakhomov, Evgeny A , Kaehler, Sven , Lutjeharms, Johan R E , Durgadoo, Jonathan V
- Date: 2010
- Language: English
- Type: Article
- Identifier: vital:6493 , http://hdl.handle.net/10962/d1004477
- Description: Eddies have some decisive functions in the dynamics of the Southern Ocean ecosystems. This is particularly true in the Indian sector of the Southern Ocean, where a region of unusually high-mesoscale variability has been observed in the vicinity of the South-West Indian Ridge. In April 2003, three eddies were studied: eddy A, a recently spawned anticyclone south of the Antarctic Polar Front (APF),; eddy B, an anticyclone north of lying between the Subantarctic Front and the APF; and eddy C, a cyclone north of the APF west of the ridge. Elevated concentrations of total Chl-a coincided with the edges of the cyclonic eddy, whereas both anticyclonic eddies A and B were characterised by low total Chl-a concentrations. Biologically, the two anticyclonic eddies A and B were distinctly different in their biogeographic origin. The zooplankton community in the larger anticyclonic eddy A was similar in composition to the Antarctic Polar Frontal Zone (APFZ) community with an addition of some Antarctic species suggesting an origin just north of the APF. In contrast, the species composition within the second anticyclonic eddy B appeared to be more typical of the transitional nature of the APFZ, comprising species of both subantarctic and subtropical origin and thus influenced by intrusions of water masses from both north and south of the Subantarctic Front. Back-tracking of these features shows that the biological composition clearly demarcates the hydrographic origin of these features.
- Full Text:
- Date Issued: 2010
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