North Atlantic Deep Water Pathways and Eddy Generation Beneath the Agulhas Current System

The Atlantic Meridional Overturning Circulation (AMOC) has long been an area of study due to its link to climate change. North Atlantic Deep Water (NADW) forms the deep water limb of the AMOC, ventilating the deep sea. Using high resolution model output, we show that NADW is strongly influenced by the Agulhas Current System as it flows into the Indian Ocean around South Africa. Eulerian analysis reveals that the high salinity signature of NADW erodes beneath the Agulhas Current System and is deflected to the south by the potential vorticity field. A Lagrangian analysis reveals a high degree of eddying and an indirect pathway into the Indian Ocean that favors the area beneath the Agulhas ring corridor, retroflection, and a southern route around the Agulhas Plateau. Of the 17 Sv of NADW in the slope current off South Africa in the South Atlantic, an estimated 10.5 Sv advect into the Indian Ocean. Deep cyclogenesis results from instabilities in the surface flow and is favored in three distinct areas: In the lee of the Agulhas Bank, where cyclones are generated as a result of an anomalously strong northwestward extension of the Current; beneath the retroflection where a dipole forms when the retroflection broadens; and to the east of the Agulhas Plateau where cyclones spin up as the Return Current meander deepens. Cyclogenesis is most frequent beneath the retroflection, but eddies dissipate within weeks throughout all regions and hence do not play a significant role in transporting NADW around South Africa