A hydrographic section from South Africa to the southern limit of the Antarctic Circumpolar Current at the Greenwich meridian

• Main Authors: Gladyshev, S., Arhan, M., Sokov, A., /Speich, Sabrina
• Format: Text
• Language: English
• Published: 2008
• Subjects: Antarctic circumpolar current; Agulhas eddies; Transport; Bottom circulation; Fronts; Water masses; Antarc*; Antarctic; Drake Passage; NADW; North Atlantic Deep Water; North Atlantic
• Online Access: https://www.documentation.ird.fr/hor/fdi:010044057

The properties and circulation of water masses leaving and entering the Atlantic Ocean south of Africa are examined using data from a hydrographic and Lowered acoustic Doppler current profiler section from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC). At the upper levels, the ACC fronts are well determined using either classical water mass definitions or gradient-based criteria. While the locations of the Subantarctic Front (SAF), Polar Front (PF), and Southern ACC Front (SACCF) seem controlled by the neighbouring ridges, that of the Subtropical Front (STF) is much influenced in this region (similar to 10 degrees E) by northwestward propagating Agulhas rings. No large amount of Subantarctic Mode Water (SAMW) is observed, but two varieties of vertically homogeneous water are found in eddies detached from the Agulhas retroflection: one is remotely (Indian Ocean) formed SAMW, and the other a local variety formed through winter convection in some eddies. The deep front imprints allow one to recognize lower circumpolar deep water (LCDW) from the Drake Passage (south of the SACCF), a mix of LCDW and North Atlantic Deep Water (NADW) injected in the ACC in the Argentine Basin (between the PF and STF), and diluted NADW from a southeastward pathway along the African continental slope (north of the STF in these data). The abyssal circulation, much controlled by ridges transverse to the ACC, shows a westward entry of diluted WSDW into the Cape Basin below the PF and two cyclonic patterns in the southern and central Cape Basin superimposed on a wider eastward trend. Transport estimates are given for the ACC, its fronts, and the abyssal circulation. The baroclinic and total ACC transports are similar to 136 and similar to 153 Sv, respectively. Bottom-intensified westward flows 0(20 Sv) have only a limited effect on the ACC net transport, being laterally compensated. They, however, affect the frontal structure: the similar to 15 Sv entry of diluted WSDW seems related to a branching of the PF, ...