Nature 325, 138 - 140 (08 January 1987); doi:10.1038/325138a0

Shedding of an Agulhas ring observed at sea

J. R. E. Lutjeharms^* & A. L. Gordon^†

^*National Research Institute for Oceanology, CSIR, P.O. Box 320, Stellenbosch 7600, South Africa
^†Lament-Doherty Geological Observatory, Palisades, New York 10964, USA

The formation of current rings by the Gulf Stream through the pinching-oif of elongated meanders^1–5 is the dominant mechanism by which mass, momentum, vorticity, chemical substances and biota are transported across it⁴. Gulf Stream rings have an important effect on the ocean regions where they are found^6,7, profoundly influencing the energy and biotic distributions and being responsible for significant ventilation of the thermocline⁸. The formation of such rings has also been observed in other western boundary currents such as the Kuroshio⁹ and the East Australian current¹⁰. The spawning of rings at the Agulhas current retroflection has thus far only been inferred from thermal infrared images obtained by satellite¹¹ as there has been no contemporaneous confirmatory evidence at depths greater than the surface layer. The production of Agulhas rings is of particular importance as it may be one of the primary mechanisms in the exchange of thermocline water between the Indian and Atlantic oceans^12,13, a significant climatic factor. We report here the occlusion of an Agulhas ring based on the first extensive set of measurements taken at sea during such an event.

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