2012/04/17 by Erik van Sebille, William E. Johns, Lisa M. Beal · 1 citation
Earth and Planetary Sciences · #Oceanographic and Atmospheric Processes #Geology and Paleoclimatology Research #Marine and coastal ecosystems #North Atlantic Deep Water #Geology #Boundary current #Potential vorticity #Thermohaline circulation #Gulf Stream #Oceanography #Climatology #Vorticity #Ocean current #Vortex #Geography #Meteorology
paper · pdf · doi:10.1029/2011jc007684
openalex publication_date 2012/04/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/23
As part of the global thermohaline circulation, some North Atlantic Deep Water (NADW) exits the Atlantic basin to the south of Africa. Observations have shown that there is a quasi‐zonal pathway centered at 25°S carrying NADW eastward, connecting the Deep Western Boundary Current to the Cape Basin. However, it has been unclear what sets this pathway. In particular, waters must move southward through the Cape Basin, thereby crossing isolines of planetary vorticity, in order to exit the basin. Here, we find that an eddy thickness flux induced by Agulhas rings moving northwestward forces a circulation of NADW through the Cape Basin. The pathway at 25°S feeds the southeastward flow of this circulation while conserving potential vorticity. Using Lagrangian floats advected for 300 years in a 1/10° resolution ocean model, we show that the most common pathway for NADW in our model lies directly below the Agulhas ring corridor. By analyzing the velocity and density fields in the model, we find that the decay of these rings, and their forward tilt with depth, results in a southward velocity, across isolines of planetary vorticity, of 1 to 2 cm/s in the deep waters. The associated stream function pattern yields a deep circulation transporting 4 Sv of NADW from the Deep Western Boundary Current at 25°S to the southern tip of Africa.