The disparate evolution of three Agulhas rings in the South Atlantic Ocean

Hydrographic sections carried out in January-March 1995 across the pathway of Agulhas rings in the Cape Basin are used for a brief description of the mesoscale thermohaline variability in this region and a detailed study of t hree rings that were identified in the data. The three eddies exhibited rem arkably diverse dimensions, vertical structures, and water mass characteris tics. One of them, RI, was located near the Agulhas retroflection, had a di ameter of 200 km, a maximum azimuthal speed of 0.40 m s(-1), core oxygen va lues in excess of 260 mu mol kg(-1) and was characterized by a well-develop ed thermostad of 11.6 degrees C. A second ring, R2, at 31 degrees 30'S, 9 d egrees W, by contrast, had a diameter of about 500 km, a core temperature o f 17.1 degrees C, and azimuthal speeds of 0.50 m s(-1), suggesting a very d ifferent history A third ring, R3, at 26 degrees S, 9 degrees W, although f arthest north of the three, had characteristics similar to ring R1, but wit h a deeper thermostad. Satellite altimetric data allow one to infer the nat ural histories of these vortices. Ring R1 detached from the retroflection a t the beginning of March 1994 and spent the whole of the subsequent winter south of 42 degrees S. This could explain the estimated heat loss of 620 W m(-2). The two rings observed at 9 degrees W were spawned as one feature in April 1993, but interaction with the Erica seamount split it into two eddi es; R3 being stalled in the retroflection region for the winter, while R2 m oved off rapidly into the South Atlantic, by contrast, retaining most of it s heat. These histories account for the observed differences, between the r ings. They also demonstrate that the interaction of Agulhas rings with thei r environment, including ambient water masses, the overlying atmosphere, an d the bottom topography, is critical to their eventual hydrographic charact eristics and the manner in which they contribute to the transport of heat a nd salt from the Indian to the South Atlantic Ocean.