Geostrophic transport in the Warm Water Sphere of the eastern subtropical North Atlantic

Abstract

Geostrophic transports in the eastern subtropical North Atlantic computed from historic hydrographic data and recent CTD measurements show a mean transport in the subtropical gyre of 11 ± 1.5 × 106 m3 s–1 in the upper 1000 m between 35W and the African coast. The dynamic method was used in conjunction with a conservation of mass scheme (Fiadeiro and Veronis, 1982) to determine the level of no motion. This level lies in the 1200 m depth near the Azores and drops to 1500 m in the tropics. \n \nThe main inflow enters south of the Azores as a relatively narrow current, turns southward at the latitude of Madeira and then widens. Three current bands transport the water southward. North of the Cape Verde Islands, the current turns westward. This part of the North Equatorial Current extends more to the south in the upper 200 m than in the 200–800 m layer. The Portugal current, between the Azores and the Portuguese coast, which is thought by some to be strong, is seen here as a relatively weak flow. \n \nMaps of potential vorticity derived from smoothed density profiles are consistent with the general pattern of geostrophic transport.