Antarctic intermediate water at the Agulhas Current retroflection region

Abstract

The inter-ocean transport of salty, warm Indian Ocean water to the Atlantic Ocean has been shown to stabilize the meridional overturning of the Atlantic. This salt and heat is mostly transported by Agulhas rings, shed at the Agulhas retroflection. To investigate the contribution of Antarctic Intermediate Water (AAIW) to this salt and heat flux, 7 hydrographic sections in the south-west Indian and south-east Atlantic Oceans were investigated using Optimum Multi-parameter Analysis. The mean contributions of AAIW from the South Indian Ocean (iAAIW) and that of the Drake Passage (dAAIW), over the density range σ n = 27.25–27.7, showed that iAAIW was the dominant AAIW type east of the Agulhas Current retroflection. The maximum contributions of iAAIW were confined to the Agulhas Current, the Agulhas Return Current and Agulhas rings. In the subdivided density ranges, iAAIW was always the dominant water type in the upper density range ( σ n = 27.25–27.4), whilst in the lower density range ( σ n = 27.4–27.7) the dAAIW/iAAIW mix was almost 50/50. West of the retroflection the mean iAAIW/dAAIW mix over the density range σ n = 27.25–27.7 was around 50/50 for the southern part of the Cape Basin. In the upper density range the average mix of dAAIW/iAAIW was 45/55, whilst for the lower density range the mix was 46/54. Section by section comparisons, however, showed considerable differences in the observed mix of dAAIW/iAAIW in both the upper and lower density ranges.