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DOI : 10.1029/2011JC007140

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Journal of Geophysical Research 116 (2011) C11004

Anticyclonic and cyclonic eddies of subtropical origin in the subantarctic zone south of Africa

Michel Arhan 1, Sabrina Speich 1, Christophe Messager 1, Guillaume Dencausse 1, 2, Rana Fine 3, Marie Boye 4

(03/11/2011)

Two eddies, one anticyclonic and the other cyclonic, intersected in the Subantarctic Zone south of South Africa during a hydrographic transect, are described using a large set of measurements including full depth hydrography, Acoustic Doppler Current Profiler velocities, biogeochemical tracers, air-sea fluxes and altimetric sea surface height. Both eddies have a subtropical origin. The anticyclone is an Agulhas ring with convected core water of ∼12°C, and swirl velocities of 1 m s−1. It was 9.5 months old when sampled and had crossed the Agulhas Ridge. Though sampled in summer, it was releasing ∼200 W m−2 (sensible plus latent heat flux) to the atmosphere. It was observed adjacent to the Subantarctic Front, illustrating the usual encounters of such structures with this front. The cyclone, marked by pronounced low oxygen and CFC anomalies revealing an origin at the continental slope, was 4.5 months old. It had swirl speeds of 0.3 m s−1, and was coupled with the anticyclone when observed. From their kinematics and water mass properties both structures were found to transport subtropical water down to ∼900 m, the water trapped below this depth being either from the northern Subantarctic Zone, or local water. The two structures illustrate the capacity of eddies in the region to transfer subtropical and alongslope water properties into the Subantarctic Zone.

1 :	Laboratoire de physique des océans (LPO)
	CNRS : UMR6523 – Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER) – INSU – Université de Bretagne Occidentale [UBO] – Institut de recherche pour le développement [IRD] – Institut Universitaire Européen de la Mer (IUEM)
2 :	Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS)
	CNRS : UMR5566 – Institut de recherche pour le développement [IRD] – CNES – Observatoire Midi-Pyrénées – INSU – Université Paul Sabatier [UPS] - Toulouse III
3 :	RSMAS/MAC
	University of Miami
4 :	Laboratoire des Sciences de l'Environnement Marin (LEMAR)
	Institut Universitaire Européen de la Mer (IUEM) – Université de Bretagne Occidentale [UBO] – CNRS : UMR6539 – Institut de Recherche pour le Développement

Domaine

:

Sciences de l'environnement

Mots Clés : mesoscale eddies

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Contributeur : Dominique Gac <>

Soumis le : Dimanche 13 Mai 2012, 07:00:07

Dernière modification le : Dimanche 13 Mai 2012, 07:00:07