Evidence that the natal pulse involves the Agulhas Current to its full depth


  • Johann R. E. Lutjeharms,

  • Olaf Boebel,

  • Paul C. F. van der Vaart,

  • Wilhelmus P. M. de Ruijter,

  • Thomas Rossby,

  • Harry L. Bryden


Natal Pulses are intermittent, solitary meanders on the trajectory of the otherwise remarkably stable northern Agulhas Current. They play disparate roles in the process of inter-ocean exchange. They have been thought to trigger the spawning of Agulhas Rings at the Agulhas Retroflection, but also to generate an upstream retroflection that prevents Agulhas water from reaching the inter-ocean boundary. For the Natal Pulse to be such a control it has to extend to considerable depths. We present the first hard evidence that demonstrates that the Natal Pulse is indeed an inherent property of the Agulhas Current throughout its full depth. Our data comprise Eulerian current meter observations and Lagrangian float trajectories in combination with sea-surface height and sea-surface temperature data. The results reveal the trapping of water within the Natal Pulse, its southward advection at a phase speed of about 11–12 cm s−1, and rotation periods of 6 days.