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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on May 3, 2009
ICES Journal of Marine Science: Journal du Conseil 2009 66(6):1063-1072; doi:10.1093/icesjms/fsp102
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© 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

This article appears in the following ICES Journal of Marine Science issue: The Ecosystem Approach with Fisheries Acoustics and Complementary Technologies [View the issue table of contents]

The response of sound scatterers to El Niño- and La Niña-like oceanographic regimes in the southeastern Atlantic

Marek Ostrowski1, José C. B. da Silva2 and Bomba Bazik-Sangolay3

1 Institute of Marine Research, PO Box 1870, Nordnes, 5817 Bergen, Norway
2 Department of Geographic Engineering, Geophysics and Energy, Institute of Oceanography, University of Lisbon, Rua Ernesto de Vasconcelos, Campo Grande, 1749-016 Lisboa, Portugal
3 Instituto Nacional de Investigação Pesqueira, Ilha de Luanda, C.P. 2601 Luanda, Angola

Correspondence to M. Ostrowski: tel: +47 55 23 53 78; fax: +47 55 23 85 31; e-mail: mareko{at}imr.no.

Ostrowski, M., da Silva, J. C. B., and Bazik-Sangolay, B. 2009. The response of sound scatterers to El Niño- and La Niña-like oceanographic regimes in the southeastern Atlantic. – ICES Journal of Marine Science, 66: 1063–1072.

Oceanographic conditions off Angola alternate seasonally between upwelling in the austral winter and El Niño-like intrusions and downwelling in summer. During winter in regions deeper than 30 m, the water column consists of a top layer of warm, tropical water overlying cold, nutrient-rich, and hypoxic South Atlantic Central Water (SACW). Closer inshore the water becomes well mixed. In the stratified region, acoustic backscatter at 38 kHz matches the oceanographic structure. It is strong in the top layer, but declines sharply in the SACW. During summer, the water column is continuously stratified, and the SACW is absent from the shelf. The backscatter reveals multiple thin layers extending across much of the shelf. The scattering layers are often perturbed by internal waves. The combined evidence from multiple acoustic surveys and the existing synthetic-aperture radar imagery suggests that tidal internal waves are a pervasive phenomenon in Angolan waters.

Keywords: Angolan upwelling, tidal internal waves, volume backscatter

Received 11 August 2008; accepted 4 February 2009; advance access publication 3 May 2009.


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