Where Three Oceans Meet: The Agulhas Retroflection Region

摘要

The Agulhas Retroflection south of Africa lies at the junction of the S. Indian, S. Atlantic, and Circumpolar Oceans. A March 1985 survey, including hydrographic stations, subsurface current path survey, and contemporaneous sea surface temperature (SST) satellite infrared image, plus historical data, are used to characterize the region. In 1985, Agulhas transport was 56 to 95 Sv (1 million m/s; relative to 2400 dbar), up to 1.5 times the interior transport from linear theory and observed winds. Return Current transport was 54 and 65 Sv. The current retroflected in two branches. The surface warm core retroflected upstream of the second branch, while an SST front, and the subsurface current path survey, followed it. A cold ring, with 64 Sv transport but no SST anomaly, and a wave recirculation lay between the branches. Curvature vorticity at anticyclonic turns in the path exceeded the gradient wind maximum, so other dynamics must locally contribute. Salt, oxygen, and potential vorticity fronts on isopycnals in the current's upper approx. 300 m are observed, as are deep western boundary filaments of Red Sea Water and N. Atlantic Deep Water influences. The current meets baroclinic barotropic instability necessary conditions. Thermocline water (>8C) transport into the S. Atlantic is 2.8 to <9.6 Sv, less than the > or = 10 Sv Atlantic export of deep water. Keywords: Agulhas currents, Oceanographic data; Optical data; Air water interactions; Western boundary current; Oceanographic fronts; Salinity; Ocean currents; Indian Ocean; South Atlantic Ocean. Theses. (edc)