Circulation of bottom waters in the southwestern South Atlantic

Abstract

Data from 137 new hydrographic stations are used with older hydrographic data to construct horizontal charts of potential temperature at 4000 m and the depth of the 0°C potential temperature surface for the southwestern South Atlantic. The data are also used to construct seven potentials temperature sections and to calculate bottom water transport. From the horizontal charts it is inferred that the abyssal circulation in the Argentine Basin and its southward extension consists of several distinct gyres. The most intense abyssal circulation is in the western Argentine Basin. It is suggested that these bottom waters are renewed by northward flow through the East Falkland Channel from the Georgia Basin. The Georgia Basin provides the most direct conduit to the western Argentine Basin for the cold, fresh bottom waters found in the vicinity of the South Sandwich Trench. The horizontal charts also indicate a southward flow from the Argentine Basin into the Georgia Basin of warmer bottom waters through the East Falkland Channel. These waters are found along the southern flank of the Falkland Fracture Zone and the eastern flank of the Islas Orcadas Rise. The vertical potential temperature sections illustrate the baroclinic structure of the western boundary currents over the South Sandwich Trench and along the Argentine Continental Slope. The calculated northward transports for waters with potential temperatures less than 0°C are largest (18 x 10 6 m 3 s −1) at the southern end of the South Sandwich Trench just north of the Weddell Sea. The transports decrease to 5 x 10 6 m 3 s −1 at the northwestern end of the trench. The major flow of cold bottom water into the Argentine Basin appears to be through the Georgia Basin, with 1 to 3 x 10 6 m 3 s −1 flowing through the Falkland Channels. A reference level is chosen in the Argentine Basin that is coincident with the depth of the 0°C potential temperature surface that on the average is 2000 m deeper than that proposed by DEFANT ( Wissenschaftliche Ergebnisse der Deutschen Atlantischen Expedition auf dem Forschungs- und Vermessungsschiff “Meteor”, 1925–1927, 6 (2, 5), 191–260, 1941) and used by Wüst ( Wissenschaftliche Ergebnisse der Deutschen Atlantischen Expedition auf dem Forschungs- und Vermessungsschiff “Meteor”, 1925–1927, 6 (2, 6), 261–420, 1957). The calculated transports for the deep and abyssal boundary currents in the western Argentine Basin are small (2 x 10 6 m 3 s −1), less than one-tenth that calculated bu Wüst (1957) for the bottom waters.