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Keywords:

  • Agulhas rings;
  • North Atlantic Deep Water;
  • vorticity dynamics;
  • water mass pathways

The southward branch of the Atlantic Meridional Overturning Circulation (AMOC), the stretch that carries deep, cold water from the North Atlantic to the Southern Ocean, predominantly flows along the eastern shoreline of the Americas. This deep water transport, known as the Deep Western Boundary Current, hits a fork in the flow at 25°S, off the coast of Brazil. Here the current splits in two, with the majority continuing its southbound journey and a smaller ribbon veering to the east. This eastbound water travels at depth across the South Atlantic, eventually passing around Africa's southern coast. In its path from Brazil to Africa the water crosses lines of consistent vorticity—essentially traveling uphill. Though researchers have known of this current for decades, little is known of what drives it.