Please use this identifier to cite or link to this item: http://hdl.handle.net/10553/71077
Title: Observations of the east Madagascar current system: Dynamics and volume transports
Authors: Voldsund, Aksel
Aguiar González, Miguel Borja 
Gammelsrød, Tor
Krakstad, Jens Otto
Ullgren, Jenny
UNESCO Clasification: 251007 Oceanografía física
Keywords: East Madagascar
In situ observations
Indian Ocean
Remote sensing
Volume transport
Western boundary current
Issue Date: 2017
Journal: Journal of Marine Research 
Abstract: The South Equatorial Current (SEC) in the Indian Ocean bifurcates when it reaches Madagascar leading, respectively, to the North East Madagascar Current (NEMC), which contours the island flowing northwestward, and to the South East Madagascar Current (SEMC), which flows southwestward. Both branches eventually contribute to the greater Agulhas Current system and thus play a part in the global ocean circulation. In addition, these currents have important effects on the local conditions for marine life. In this study, the NEMC and the SEMC are investigated based on a comprehensive, multidisciplinary survey of the east coast of Madagascar in 2008. Results from conductivity-temperaturedepth stations, underway measurements with thermosalinograph and fluorometer, and ship-mounted acoustic Doppler current profiler are discussed along with concomitant remotely sensed data. Maximum core velocities of >150 cm s-1 were observed in both the NEMC and the SEMC. The SEMC appeared as a nearshore southward jet, which extended at its widest nearly 200 km offshore. Near the southern tip of Madagascar, the SEMC was flanked by reverse velocities: a northeastward current about 30 km wide along the coast and a northeastward offshore current greater than 140 km wide suggesting the presence of the South Indian Ocean Countercurrent. The NEMC had the structure of a narrow nearshore jet, with weak currents beyond 100 km offshore. Volume transport for the upper 1,100 m was estimated to be 22 Sverdrup (Sv) for the SEMC and 48 Sv for the NEMC. The high NEMC transport compared with earlier estimates might be because of anomalously high influx of the SEC during the measurement period. Off the south coast, an undercurrent below 900 m carried an equatorward transport of 3.1 Sv. No undercurrent was observed in the north, but a geostrophic velocity minimum and a similar vertical velocity shear between surface and subsurface currents were found at the level where such a countercurrent has been previously observed from direct measurements.
URI: http://hdl.handle.net/10553/71077
ISSN: 0022-2402
DOI: 10.1357/002224017821836725
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