Where three oceans meet : the Algulhas retroflection region

• Main Author: Bennett, Sara L.
• Format: Thesis
• Language: English
• Published: Massachusetts Institute of Technology and Woods Hole Oceanographic Institution 1988
• Subjects: Ocean currents; Ocean temperature; Thomas Washington (Ship) Cruise 3; Knorr (Ship : 1970-) Cruise; Oceanus (Ship : 1975-) Cruise; Curl; Indian; North Atlantic Deep Water; North Atlantic
• Online Access: https://hdl.handle.net/1912/4761

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1988 The highly energetic Agulhas Retroflection region south of the African continent lies at the junction of the South Indian, South Atlantic, and Circumpolar Oceans. A new survey of the Agulhas Retroflection taken in March 1985, plus historical hydrographic data, allow its dynamical and water-mass characteristics, and its role in exchanging mass, tracers, and vorticity between the three oceans, to be extensively characterized. The 1985 survey is composed of three independent, synoptic elements: a grid of closely-spaced, full-water-depth hydrographic stations (the first entirely full-water-column survey in this area), including several transects of the Agulhas and Agulhas Return Currents; a continuous survey of the path of the currents (the first such survey in the Agulhas); and a contemporaneous and relatively cloud-free sea surface temperature image derived from satellite infrared measurements. Mass transport balances within the closed grid boxes of the 1985 hydrographic survey provide information about current transport, recirculation (transport in excess of estimated returning interior ocean transport), and the overall Retroflection transport pattern. The current transport values exceed by as much as a factor of 1.5 the maximum interior transport computed from observed wind-stress curl and linear theory. Agulhas Current transports ranged from 56 to 95 x 106 m s-l at four 1985 transects crossing the current. Agulhas Return Current transports at the two 1985 transects were 54 and 65 x 106 m s-l. These transports are computed relative to 2400 dbar, which lies below the deep oxygen minimum emanating from the South Indian Ocean, and above the North Atlantic Deep Water salinity maximum. The current retroflected in two distinct branches in 1985, with a cold ring and a partially isolated warm recirculation cell found between ...