Date of Award


Degree Type


Degree Name

Doctor of Philosophy in Oceanography




The exchange of waters from the Indian to the Southeast Atlantic has been postulated as a key link in the meridional overturning circulation of the ocean. The Agulhas South-Atlantic Thermohaline Transport Experiment, ASTTEX, moored an array of pressure recording inverted echo sounders (PIES) and current meters, January 2003 - March 2005, along a Jason satellite altimeter ground-track south- west of South Africa. The transect spanned the “eddy corridor" where Agulhas rings pass, carrying cores of Indian Ocean water into the South Atlantic. The array was designed to quantify the salt and temperature fluxes attributable to passage of Agulhas rings and eddies.

This work investigates the combined barotropic and baroclinic sea surface height (SSH) variability across an eddy corridor in the Southeast Atlantic Ocean using pressure-sensor equipped inverted echo sounders and compares these results with satellite altimetry data. The barotropic component contributes substantially to the total SSH anomaly: an average of 47% of the total SSH during periods when the SSH anomaly exceeds 15 cm, and 20% of the overall SSH variance. Interestingly the barotropic timeseries data have about twice the spatial correlation scale of the baroclinic timeseries data: 200 km compared to 110 km. Cases of strong barotropic cyclonic eddies are almost always vertically aligned with baroclinic eddies. Moreover, most baroclinic anticyclonic eddies were laterally coupled to a mixed baroclinic-barotropic cyclonic eddy before or during transit across the ASTTEX array.

Observations suggest that the baroclinic eddies translate within this region substantially faster than predicted for isolated linear eddies affected only by planetary-b, and the weak mean background °ow does not control their propagation. Baroclinic cyclonic and anticyclonic eddies propagated with speeds of 7.5 cm s-1 on average, and barotropic cyclonic and anticyclonic eddies propagated with speeds of 13.5 cm s-1 on average. Vortex-vortex interaction processes play an important role in eddy propagation, fostering the transport of water properties in eddies, as they transit through the ocean and contribute to thermocline waters.



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