Research Articles

Decay of eddies at the South-West Indian Ridge

Jonathan V. Durgadoo, Isabelle J. Ansorge, Beverly A. de Cuevas, Johann R.E. Lutjeharms, Andrew C. Coward
South African Journal of Science | Vol 107, No 11/12 | a673 | DOI: https://doi.org/10.4102/sajs.v107i11/12.673 | © 2011 Jonathan V. Durgadoo, Isabelle J. Ansorge, Beverly A. de Cuevas, Johann R.E. Lutjeharms, Andrew C. Coward | This work is licensed under CC Attribution 4.0
Submitted: 25 March 2011 | Published: 03 November 2011

About the author(s)

Jonathan V. Durgadoo, Department of Oceanography, University of Cape Town, South Africa
Isabelle J. Ansorge, Department of Oceanography, University of Cape Town, South Africa
Beverly A. de Cuevas, Marine Systems Modelling Group, National Oceanography Centre, University of Southampton, United Kingdom
Johann R.E. Lutjeharms, Department of Oceanography, University of Cape Town, South Africa
Andrew C. Coward, Marine Systems Modelling Group, National Oceanography Centre, University of Southampton, United Kingdom

Abstract

The South-West Indian Ridge in the Indian sector of the Southern Ocean is a region recognised for the creation of particularly intense eddy disturbances in the mean flow of the Antarctic Circumpolar Current. Eddies formed at this ridge have been extensively studied over the past decade using hydrographic, satellite, drifter and float data and it is hypothesised that they could provide a vehicle for localised meridional heat and salt exchange. The effectiveness of this process is dependent on the rate of decay of the eddies. However, in order to investigate eddy decay, logistically difficult hydrographic monitoring is required. This study presents the decay of cold eddies at the South-West Indian Ridge, using outputs from a high-resolution ocean model. The model’s representation of the dynamic nature of this region is fully characteristic of observations. On average, 3–4 intense and well-defined cold eddies are generated per year; these eddies have mean longevities of 5.0±2.2 months with average advection speeds of 5±2 km/day. Most simulated eddies reach their peak intensity within 1.5–2.5 months after genesis and have depths of 2000 m – 3000 m. Thereafter they dissipate within approximately 3 months. The decay of eddies is generally characterised by a decrease in their sea surface height signature, a weakening in their rotation rates and a modification in their temperature–salinity characteristics. Subantarctic top predators are suspected to forage preferentially along the edges of eddies. The process of eddy dissipation may thus influence their feeding behaviour.

Keywords

eddy kinetic energy hotspot; Southern Ocean; DEIMEC; OCCAM; Prince Edward Islands

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