South Atlantic deep eastern boundary current driven by Agulhas rings: An idealized study

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The deep eastern boundary current (DEBC) in the southeast Atlantic Ocean plays an important role in the global meridional overturning circulation, by carrying a comparable fraction of the North Atlantic Deep Water transport toward the Southern Ocean to that of the deep western boundary current. At the same time, the southeast Atlantic Ocean is constantly influenced by energetic Agulhas rings that are shedded by the Agulhas current. It has been pointed out that the eddy thickness transport by these Agulhas rings is important in enabling the deep water mass that flows southeastward within the interior of the South Atlantic Ocean to cross isolines of large scale potential vorticity toward the eastern boundary where it feeds the DEBC. In this work, we focus on the dynamics of DEBC itself which carries this water mass into the Southern Ocean. We use idealized general circulation model configurations to study the relationship between the Agulhas rings, bathymetry and the southward DEBC in southeast Atlantic Ocean. We find that a DEBC comparable to that in observations and state estimate products is obtained only with combined forcing by Agulhas rings and a sloping bathymetry. The DEBC is then characterized by a mid-depth core at a 2.2 km, again similar to observations. We analyze the momentum and vorticity budgets of the DEBC and show that it is driven by vortex stretching that is sensitive to both eddy temperature transport and the bottom slope.