Water masses and currents of the Southern Ocean at the Greenwich Meridian


  • Thomas Whitworth III,

  • Worth D. Nowlin Jr.


The frontal structure of the Antarctic Circumpolar Current (ACC) at the Greenwich Meridian is similar to that at Drake Passage even though the current is not confined to flow between two continents: There are sharp horizontal gradients in all properties throughout the water column, the fronts are narrow relative to the total width of the current, and most of the transport occurs within the frontal zones. East of Drake Passage, saline North Atlantic Deep Water (NADW) is incorporated into the Circumpolar current, and at the Greenwich Meridian it influences the water characteristics as far south as the Polar Front. Although the transport between Antarctica and Africa is close to that between Antarctica and South America, the transport within the ACC at our section is about 20% greater than at Drake Passage, probably due in part to the addition of NADW. Separating the ACC from the Weddell Gyre is a sharp front, south of which the signature of all but the densest Circumpolar Deep Water (CDW) is lost by mixing with the surface waters. The intermediate water of the central Weddell Gyre is formed from this dense CDW, which is modified by biochemical processes to become oxygen poor and nutrient rich. Warm, salty, less dense CDW from the southern edge of the ACC rounds the eastern end of the gyre and appears in the southern limb, which meanders around Maud Rise.