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

Michel Arhan, Sabrina Speich, Christophe Messager, Guillaume Dencausse, Rana A Fine, Marie Boye

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Article numberC11004
JournalJournal of Geophysical Research C: Oceans
Volume116
Issue number11
DOIs
StatePublished - 2011

Fingerprint

eddy
vortices
Water
water
anticyclones
anticyclone
hydrography
sea surface height
CFC
Acoustic Doppler Current Profiler
chlorofluorocarbons
latent heat flux
sensible heat flux
Chlorofluorocarbons
cyclones
continental slope
Republic of South Africa
cyclone
Latent heat
water mass

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Oceanography

Cite this

Anticyclonic and cyclonic eddies of subtropical origin in the subantarctic zone south of Africa. / Arhan, Michel; Speich, Sabrina; Messager, Christophe; Dencausse, Guillaume; Fine, Rana A; Boye, Marie.

In: Journal of Geophysical Research C: Oceans, Vol. 116, No. 11, C11004, 2011.

Research output: Contribution to journalArticle

Arhan, Michel ; Speich, Sabrina ; Messager, Christophe ; Dencausse, Guillaume ; Fine, Rana A ; Boye, Marie. / Anticyclonic and cyclonic eddies of subtropical origin in the subantarctic zone south of Africa. In: Journal of Geophysical Research C: Oceans. 2011 ; Vol. 116, No. 11.
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