Frontal structure and transport of the Antarctic Circumpolar Current in the south Indian Ocean sector, 40–80°E

Abstract

Based on recent conductivity-temperature-depth (CTD) data at the Kerguelen-Amsterdam passage plus historical expendable bathy thermograph (XBT) and hydrographie data from the Crozet Basin, the frontal structure and volume transport of the Antarctic Circumpolar Current (ACC) in the south Indian Ocean sector are described. Recent findings on sea-level variability from GEOSAT altimeter data are reviewed as well as barotropic transport variability from bottom pressure measurements at Kerguelen and Amsterdam Islands. The ACC here is mostly concentrated in a narrow frontal zone of 2–3° of latitude, without any noticeable multi-band structure, as a result of the confluence of the Subantarctic and Subtropical Fronts. The Polar Front in this sector is not associated with any prominent current core. This regional particularity of the ACC was further supported by GEOSAT altimetry data. About 80% of the ACC transport (106Sv; 1 Sv=10 6 m 3s −1) passes north of Kerguelen, concentrated along the northern flank of the Kerguelen Plateau; only 30 Sv passes south of Kerguelen. The bottom-pressure-derived barotropic transport variability at Kerguelen-Amsterdam passage was estimated to lie between 10 and 30 Sv, consistent with findings at Drake Passage. It is suggested that the study area constitutes a prominent ACC observatory during the WOCE (World Ocean Circulation Experiment).