Abstract
AbstractPassive tracers are advected in a Southern Ocean State Estimate (SOSE) to map the pathways of Agulhas waters, with a focus on determining where the Agulhas waters intrude into the Antarctic Circumpolar Current (ACC). Results show that Agulhas waters spread into all three ocean basins within 3 years of release. After leaving the African continent, the mean Agulhas water pathway tilts northwest toward the South Atlantic and southeast toward the ACC. The majority (from 60% to 100% depending on specific water mass) of the Agulhas waters stay in the South Indian Ocean north of the Sub‐Antarctic Front. From 10 to 28% enters the South Atlantic Ocean through the boundary current along the southern tip of South Africa and via Agulhas rings in the retroflection region. Up to 12% of intermediate depth Agulhas waters enter the ACC. Most of the tracer transport into the ACC occurs just downstream of the Kerguelen Plateau, which clearly demonstrates the importance of topography in elevating cross‐frontal exchange. Agulhas waters also contribute to Sub‐Antarctic Mode Water formation in the Southeast Indian Ocean by lateral advection. The surface Agulhas waters are preconditioned by strong surface buoyancy loss before turning into mode water, while the intermediate Agulhas waters are advected to the mode water formation region along isopycnals before being drawn into the mixed layer.
Highlights
The Agulhas Current, the swift boundary current along the southeast coast of the African continent, is one of the major western boundary currents in the world oceans
Less attention has been paid to the effect of the Agulhas leakage which is extensively discussed elsewhere [Beal et al, 2011, and the references therein]; instead, we focus on the southeast pathways of Agulhas waters and find that the contributions of the Agulhas waters to the Southeast Indian SAMW (SEISAMW) and the Antarctic Circumpolar Current (ACC) water are not negligible
Using Southern Ocean State Estimate (SOSE) we carry out a series of passive tracer experiments initialized within an 118 wide zonal section at 298S to map the pathways of water originating in the Agulhas current system
Summary
The Agulhas Current, the swift boundary current along the southeast coast of the African continent, is one of the major western boundary currents in the world oceans It carries warm and saline Indian, Arabian Sea, and Red Sea waters southward along the southeast African coast [Harris, 1972; Lutjeharms, 1976; Biastoch and Krauss, 1999; Beal et al, 2006]. This transport of warm and saline Indian water by the Agulhas leakage is referred to as the ‘‘warm water route’’ in the global conveyer belt schematic [Gordon, 1986] It compensates the southward export of the North Atlantic Deep Water (NADW) formed in the sub-Arctic North Atlantic and plays an important role in the global ocean circulation and climate [Beal et al, 2011; Caley et al, 2012].
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